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WORKING
WITH
PEWTER
INTERNATIONAL TIN RESEARCH INSTITUTE
Fraser Road, Perivale, Greenford, Middlesex
Tel: 01-997 4254
(I.T.R.I. Publication No. 566)
CONTENTS
INTRODUCTION
CHAPTER I CHAPTER II
CHAPTER 111 CHAPTER IV
CHAPTER V
CHAPTER VI CHAPTER VI1
CHAPTER Vlll
CHAPTER IX
CHAPTER X
HISTORY PRODUCTION AND PROPERTIES OF THE METAL Alloying
Casting into ingots
Making pewter sheet
Standards for pewter
Properties of pewter
INTRODUCTION TO MAKING PEWTERWARE CAST1 N G Gravity die casting
Casting in silicone rubber moulds
Casting by lost-wax method
Centrifugal casting
Pressure die casting
SPINNING Buffing and polishing
OTHER METALWORKING PROCESSES SOLDERING OF PEWTER Attaching bases to tankards
Joining side-seamed tankards
Soldering a spout on a coffee pot
Spot weldips
DECORATIVE FINISHES Chemical treatments
Engraved designs
Mechanical engraving
Etching of pewter
PEWTER FOR THE HOBBYIST Relief work
Forming in hardwood moulds
Pewter jewellery
Simple castings
ELEMENTS OF PEWTER DESIGN Pewter drinking vessels
Pewter around the world
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INTRODUCTION
Pewter largely consists of tin, but because pure tin would be too soft for practical use, small amounts of other elements such as copper, antimony and occasionally bismuth are added to harden it. Although in older times varying amounts of lead were used in pewterware, pewter alloys are now virtually lead-free and therefore non-toxic, the lead content being strictly limited, principally on health grounds because of the use of pewter for food and drink. Moreover, modern pewter does not tarnish but retains its as-purchased condition for long periods with proper care. The darkening of most antique pewter, due to the action of the atmosphere, results from the presence of lead in those alloys. This matt or blackened appearance is prized by some collectors as having aesthetic virtues. A similar finish, when required, can be produced on the surface of modern pewter (in which lead is not an alloying element) by a chemical treatment. In fact today's pewter can have many faces, from a highly reflective, polished look to a duller, satin appearance; but whatever the finish, it can be maintained by a simple washing in warm soapy water followed by careful drying with a soft cloth. Pewter items should not be placed in dish washing machines because the high temperature drying cycle could have a deleterious effect, leading to water marks being engrained in the metal surface.
Pewter offers new incentives to the designer, who should bear in mind that the metal has a character of its own, quite distinct from that of, say, silver or stainless steel. It can be cast a t fairly low temperatures and shows good fluidity and mould- filling properties. Pewter is soft compared with metals like copper or brass and it may be hand worked by hammering or pressing and decorated by engraving directly on the surface. One important method of manufacturing hollow-ware in pewter is by spinning on a lathe, starting from flat metal sheet.
Although pewter is an ancient material, it also has a timeless character. For the designer, there is a long tradition on which to draw as well as potential for innovative approaches to working the metal to create new forms. For the purchaser, pewter also represents an investment in tin, a metal whose value is clearly established in the metal markets. Moreover, the contemporary pewter bought today may well become the prized antique of tomorrow, alongside the tappit hens and porringers of a bygone age.
In the following pages, some guidance is provided for those craftsmen who wish to widen their acquaintance with pewter and for the student or beginner who is interested in trying his hand a t working with this most amenable metal.
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CHAPTER I - HISTORY
The craft of pewtering dates back to before the time of the Roman Empire. In fact, the earliest known example of a pewter vessel is the so-called "Pilgrim bottle" from Abydos, belonging to the Egyptian 18th Dynasty of about 1500 B.C. Analysis has revealed that this bottle was made from an alloy containing 93% tin, 6% lead and 1 % copper. Few other artlcles of any significance before the 11th Century A.D. have been found but from the 14th to the 16th Century, more tin was used in England to make pewter (generally an alloy of about 80% tin with 20% lead) than for any other application. This period saw the replacement of many household utensils in stone, wood, clay and leather by their equivalent in pewter. Many churches also used an alloy of tin, lead and copper for organ pipes. A pewterers' Guild was established in Germany, a t Nurnburg in 1285 and by the middle of the 14th Century, Guilds and Associations began to spring up throughout Europe. One of the earliest records of such an Association refers to the formation of the Worshipful Company of Pewterers in London in 1348. The ordinances drawn up by this Company covered a number of points touching on the quality of the wares and conditions of work for pewterers. In 1503 the Worshipful Company established maker's touchmarks and it was required that these and other marks used by the craftsman be recorded on "tablets of pewter" kept at the Company's headquarters.
A Guild was set up in Sweden in 1485, but although pewterware was being made in the Netherlands, at Dordrecht, a t the end of the 13th Century, a pewterers' Guild was not established there until 1651, a t Leiden.
By this time, pewter articles were to be found in most middle-class homes as well as in inns and taverns. The European popularity of pewter a t this time is attested by the fact that pewter was second only to cloth as the most valuable manufactured commodity exported from England. By the end of the 16th Century there was scarcely a city in Europe without a pewterers' Guild. This was particularly true of France and Belgium where Paris, Bordeaux, Marseilles, Toulouse, LiBge, Ghent and Bruges were notable examples of cities with flourishing pewterware manufacturing industries.
Meanwhile pewter had been introduced to the households of colonial America. The first pewterers came from England and were reported to be at work in Boston, New York and
Philadelphia as early as 1640; however, no pieces can be positively identified as having been produced in North America before 1700. The years between 1700 and 1850 marked a tremendous upsurge of pewterware production there, but after this period, new developments in china porcelain caused a decline in popularity of pewterware. It was, however, during the 19th Century that most of the great American pewter craftsmen lived and worked, using the new pewter known as Britannia Metal, from which lead was excluded as an alloying element.
The invention of this Britannia Metal, in which tin was the main constituent, towards the end of the 18th Century, provided some new markets for pewterware but also did much harm to the industry through deliberate abuse. Since this new alloy could be spun more easily on a lathe than could previous pewter alloys, some manufacturers resorted to producing goods having insufficient thickness for practical use. One advantage of the introduction of Britannia Metal however, was the fact that it widened the scope of the pewterware industry, since the range of articles produced in the new alloy was wider and included such items as fancy tableware and coffee pots.
China, earthenware, pottery, glass and enamelled iron were introduced a t about the middle of the 19th Century. These were all less expensive than pewter and adversely affected the pewterware trade. The skill and craftsmanship of the pewterers eventually began to overcome this difficulty although for many years pewter failed to regain its past popularity.
The 20th Century has seen a revival of interest in pewter and antique reproductions together with new designs have developed. During this period, modern pewter Guilds and Associations have been established in many of the important pewter producing countries of the world. The first of these was the American Pewter Guild Ltd., which was founded in 1958 to preserve the high quality of modern pewter, to ensure that the customer will have the best possible product available and to promote an increased appreciation and use of contemporary pewterware. The Guild has established high standards of quality and craftsmanship for pewterware which must be met by its members. It is in the process of developing a Certification Programme for the purpose of assuring the quality of pewterware items to the purchaser, and a registration logo will be stamped on members' products.
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, over 350 years old; Walden, New York.
In 1970 the Association of British Pewter Craftsmen (A.B.P.C.) was formed and pewter articles conforming to the specifications of the Association bear a touchmark incorporating the letters A.B.P.C. within a circle. Purchasers of pewterware bearing this touchmark are assured that the article is of genuine British pewter containing a t least 90% tin, with the balance made up of copper, antimony and/or bismuth and has been produced to the high standards of crafts- manship laid down in the Association agreement.
Germany is a major producer of pewterware with an industry centred around Munich in the South and Essen in the North. In 1973 a Pewter Quality Association, the Gutegemeinschaft Zinngerat was formed with the object of promoting and ensuring good quality in the German pewter industry. A
new touchmark was also established for use by members of the Association. Since 1974, there has been a Belgian Pewter Association, the Chambre Syndicale des Maftres Etainiers de Belgique, whose aims are to control standards of purity for the pewter alloy used by its members and to encourage a spirit of co- operation amongst Belgian pewterers. As an organised body, it considers it has more scope for maintaining standards of craftsmanship and quality and can further the interests of the Belgian pewter industry. As a guide for the buying public, all pewterware made or sold by members bears a label as well as a touchmark, which guarantees that the alloy contains a t least 92% tin, the remainder being made up of antimony and copper.
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CHAPTER II - PRODUCTION AND PROPERTIES OF THE METAL
Pewter is a high-tin alloy containing some antimony to harden it and a little copper to improve its workability. Commonly used pewter alloys contain up to 6% antimony and about 2% copper. Large additions of copper are avoided since they tend to darken the colour of the pewter and could have a deleterious effect in spun pewterware; antimony tends to make the alloy whiter in colour and also improves castability s o m e w b k Small amounts of bismuth may be present 'and silver is added on occasion to influence the hardening properties.
Tin is an easy metal to deal with, on account of its non-toxicity and its rather special properties which include: low melting point (232OC1, good fluidity when molten, relative softness and good formability. These properties largely extend to pewter. The melting operation is easily performed on account of the low melting point and very low
vapour pressure of tin, and can be conducted in a hemispherical cast iron pot or a rectangular, welded mild steel vessel. One manufacturer melts pewter in a gas-fired melting pot of 5 tonnes capacity, the metal being removed in ladles and cast into moulds so as to produce 30 kg ingots. However, unless large-scale production is envisaged, it is probably more convenient to buy ingots for casting and sheet or blanks for spinning, from a commercial supplier of these materials.
Alloying To make up a pewter alloy, the tin is melted first, without a flux cover, and -then the alloying elements are dissolved in the melt. Copper is added as wire, strip or foil; tinned copper wire is sometimes used, since by its nature it wets immediately and dissolves rapidly. Antimony may be added as solid lumps; these lumps will readily
Making up a pewter alloy by adding tin ingots to a melting pot.
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dissolve once they are wetted by the tin. However, if they are not wetted, they remain undissolved in the melt and float on the surface. For this reason, additions should not be made in powder form as these are difficult to wet satisfactorily. To aid the wetting process when making additions, copper and antimony should be dipped in flux just prior to their addition to the molten tin; an aqueous solution of zinc chloride or zinc ammonium chloride constitutes a suitable flux.
Provided these recommendations are followed, complete solution can be obtained without the bath temperature exceeding 40OoC. Alloying should be carried out at the lowest possible temperature which will achieve the desired results and the craftsman would be well advised to experiment in order to find the optimum temperature for making his alloy composition. One convenient method of alloying involves making up 'master alloys' such as 50% tin - 50% antimony and 90% tin - 10% copper which are then added to the molten tin in carefully calculated amounts. Care must be taken to ensure that these alloys are completely dissolved and the, melt should be stirred with a steel paddle to ensure that small pieces of the alloying addition all dissolve, Should some overheating occur accidentally, then the melt should be left to cool undisturbed until the correct casting temperature is attained, when it should be skimmed carefully and stirred. Note: remelting alloy which _has solidified in a pot requires extreme care. Heating must be done in such a manner that a liquid pipe is produced vertically in the pot. If bottom heating is attempted without a liquid pipe, violent ejection of metal may occur when the pressure of the expanding liquid erupts through the still solid top surface and the pot itself may be damaged by distortion.
Casting into ingots When alloying is complete, the pewter is either cast into ingots for use in producing cast pewterware, or else is cast as slabs for subsequent rolling to sheet. The moulds are customarily made of cast iron and they may be water-cooled on the exterior surface. They are commonly made with lugs on one side through which pass hinges so that the two halves of the mould open and close like a book. The interior of the moulds must be dry before casting, otherwise molten metal may be ejected from the mould due to rapid formation of steam, with hazard to the operator,
Pewter slabs which are to be rolled may be cast either horizontally or in a vertical book-type mould. With horizoiital casting, directional solidification is induced by cooling the underside of the mould, using water or air jets. A depression will be formed in the top surface of the ingot due
to shrinkage and this may be eliminated in the final ingot by feeding more metal just before the metal finally solidifies. To prevent dross and oxide being cast with the metal, the metal should be poured from a point below its free surface; if this is not possible, then the surface must be skimmed before pouring. Casting temperatures should not be more than 50% above the melting point, or coarse-grained ingots can result and segregation may be promoted. For subsequent rolling to sheets, an exceptionally good surface finish is required and the ingot should be 'scalped' on top and bottom faces before rolling, using a milling machine. This shaves away the outer, rough, surfaces of the metal. More detailed information on the melting and casting of tin and tin alloys is available in I.T.R.I. Publication No. 456.
Making pewter sheet As-cast slabs, 2in (50 mm) thick, are reduced on a breakdown mill and successive reductions are then effected on a subsequent rolling mill. The rolls must have a high degree of finish, at least for the final reduction stage and care must be taken to avoid embedding foreign particles in the soft surface since these could eventually show up as imperfec~ons in a final pewterware item.
When pewter sheet is to be formed by spinning or deep drawiag techniques, it is important that the deformation properties of the sheet are uniform in all directions. Directional or 'anisotropic' properties will result in the walls of a formed vessel having non-uniform thickness and will cause the appearance of a wavy edge around the rim of the article. These uneven edges or 'ears' are both inconvenient and wasteful of material since they have to be trimmed away to give a regular edge. Work at the Institute has shown that anisotropy can be minimised in rolled pewter sheet by turning the sheet through an angle of 90' at a specific stage of the rolling schedule. As an alternative to this cross rolling, the sheet may be heat-treated a t 175'C for 10 minutes a t a certain stage before the final rolling reduction. The final reduction required to give minimum anisotropy depends on the alloy composition and the total reduction from cast slab to final thickness. Details are given in I.T.R.I. Publication No. 464.
After rolling to the final gauge, which may typically be in the range 0.025 - 0.075 in (0.6 - 1.9 mm), the sheet is often stamped into blanks of convenient size and shape for subsequent processing. Although a premium is charged by manufacturers for supplying these blanks, the convenience for the pewterer often outweighs this cost.
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Standards for pewter
DIN 17810 1974
Sn Sb 2 Cu 1.5
Sn Sb 5 Cu 1.5
A number of countries now have national standards for pewter; these are summarised below: I I
balance
balance
Standard Specification, Tin 4ntimony Copwr I I B.S. 5140 1974
Alloy A at least
90-91
90-93
95-98
5- 7
3-5
1 .O-3.0
3.7-7.0
6- 8
5-7.5
1 .O-3.0
1 .O-2.5
1 .O-2.5
1 .o-2.0
1 .o-2.0
0.25-2.0
1.5-3.0
1 .o-2.0
Properties of pewter Pewter has a distinctive white colour all its own, which is subtly different from that obtained with silver or stainless steel items. The metal, like tin itself, is soft and this softness is somehow apparent in the appearance of vessels fabricated in pewter, which have a unique tactile quality. Modern pewterware is safe for the serving of food and beverages without danger of contamination since if it is made according to National Standards or to Association qualities, lead is not added as an alloying element; the alloy has a high resistance to almost all weak acids. Pewter exceeds most other alloys in ductility; it can be stretched, compressed, hammered and bent into any desired shape. By correct selection of alloy composition a material suitable for forming by spinning or pressing can be produced. It becomes softer on working, so that annealing is not necessary. In this connection it is an ideal material for the home craftsman as well as lending itself to modern production techniques. However, this very softness imposes certain design limitations which have to be borne in mind when planning an item of pewterware. The material is not suitable for producing sharp edges as in filigree decoration, or
Lead
0.5 max
0.5 max
0.5 max
0.5 max
0.05 ma,
0.05 ma)
0.05 ma)
Comments
Other compositions are permitted provided lead and cadmium are not more than 0.5% and 0.05% respectively and tin is not less than 91%. Elements other than tin, antimony, copper, nickel, bismuth, cobalt and silver shall not be more than 0.2%.
Tin should conform to DIN 1704 (99.75% tin), antimony should be 99.6% pure and copper should conform to DIN 1708 (99.90% copper).
Arsenic should not exceed 0.05% nax, iron 0.015% max and zinc 3.005% max.
for pierced designs. When designing coffee pots to be in pewter, there is an optimum size beyond which the weight of hot liquid could lead to distorrion of the vessel; the same qualification applies to trays where weights have to be withstood by unsupported pewter sheet, which has a tendency to 'creep' under its own weight especially at temperatures much above ambient. This should not give the impression that pewter articles are to be looked at, but not used; pewter coffee and tea sets, pipe racks, cigarette boxes, vases, dishes, bowls and drinking vessels of all kinds all function perfectly well in everyday use. Cutlery has been produced with steel cutting edges and decorated pewter handles, a nice solution to the design problem of combining attractiveness with functionality. The normal method of joining pewter components is by soldering. Because of the low melting point, this can be easily achieved using a gas-air torch. However, great cars is required since the melting point of solder and of pewter are very close, particularly in those cases where lead-free solder must be used. This is dealt with more fully on pages 23 and 24.
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CHAPTER ill 9 INTRODUCTION TO MAKING PEWTER WARE
The properties of pewter are such that the material lends itself to simple crafting techniques, suitable both for the hobbyist or small-scale craftsman and for large-scale manufacturing methods. Quite effective pewter decorations can be made using only a few simple hand tools and although more sophisticated techniques are being introduced into the pewter industry, traditional equipment is relativeiy simple, consisting of a melting pot, a series of two-part moulds and lathes for spinning and turning. The two principal methods of making pewterware are by casting and by forming from sheet.
The most used method of making cast pewterware is by gravity casting into a gunmetal or cast-iron mould which may be hand held or supported in some other way. The metal is poured from a ladle and normal practice is to begin with the pre-heated mould held almost horizontal and then gradually to raise one edge until the mould assembly is in a vertical position, as the metal fills the cavity. By adopting this procedure, there is less risk of porosity in the casting. Cooling is hastened by applying cloths soaked in water to appropriate parts of the mould and the mould can be opened in quite a short time. Appendages such as handles or spouts are cast hollow by slush casting. This involves pouring metal into the mould (which is usually held in the gloved hand) and almost immediately pouring it out again, so that only a shell of metal has time to solidify in contact with the walls of the mould.
Small items can be produced in multiple quantities by centrifugal casting in rubber moulds. Molten pewter is ladled into a rapidly rotating mould made of two flat rubber discs which contain mould cavities between them and the pewter is urged into these cavities from a central feed hole, by centrifugal force. Art castings are usually
produced as a single unique casting and the ‘lost wax’ process, traditionally used for casting sculptures, is often employed. In this technique a wax ’pattern’ which represents the art work, is coated with a refractory slurry which is allowed to dry. The wax is then melted out and the refractory is fired to a hard mass, to produce a mould into which pewter can be cast. The refractory is then broken away to reveal the art work cast in pewter.
The processes of the engineering plant have been introduced to the pewter industry by some large manufacturing companies; these techniques include pressure die casting (by which large numbers of small castings are automatically produced to a standard design) and drawing, pressing and stamping methods.
Flat sheet in the form of a disc IS the starting point for spun pewterware and spinning techniques, whereby the metal is formed over a shaped block on the lathe, are used to produce much hollow- ware. Pewter articles produced by spinning are generally lighter than their cast counterparts and are therefore cheaper. They are also rather less robust, their strength depending largely on the thickness of the starting sheet. Designs produced by spinning cannot have the complex ornamentation which is possible in cast pewter, but spun pewterware is often praised for its simplicity of outline. Each type of pewterware has its own devotees and there are some regional Dreferences.
Simple tankards are conveniently made by folding sheet into a hollow cylinder and making a soldered side seam. This tube or ’collar’ is placed over a mandrel on a lathe for final forming by spinning. Pewter can also be formed by hammering, planishing and stamping. All these techniques are discussed in some detail in the following Chapters.
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CHAPTER IV - CASTING
The traditional technique of making cast pewterware is by gravity casting into permanent moulds. Semi-permanent mould casting is used for making short runs of pewterware, and for art casting. There are also a number of newer techniques such as centrifugal casting in rubber moulds and pressure die casting.
.-. Gravity die casting In this technique, molten pewter is Iqdled into a metal mould, or die and allowed to solidify. The casting may then be machined on a lathe to produce a iustrous finish. The majority of these dies are made from gunmetal although cast iron and steel moulds are used on occasion; they are usually in a t least two parts, with locating bolts for accurate registration. Many of these moulds are very old but are still in use for making reproduction items, indeed they are prized by the Dewterer for their historical value.
The moulds are pre-heated, usually by making several 'dummy runs'. When they get excessively hot they may be dipped in water containing some lime; this provides a thin coating on the cavity surfaces which improves the surface finish of the casting and helps its separation from the mould. Care must be taken that the interior coating has dried thoroughly before recommencing casting, in order to ensure there will be no evolution of steam
Gravity die casting of pewter. The mould is gradually raised to a vertical position as the molten pewter is ladled into it.
when hot metal is poured in. The temperature of the molten pewter must be carefully controlled and the casting temperature varies widely with the type of article being cast. Large platters of thin section may require a metal temperature of over 4OO0C for filling of the moulds. Before being used for casting, the mould has to be given a suitable dressing or coating on the cavity surfaces. One traditional mould coating consists of a mixture of pumice stone dust, mineral earth and the white of an eyg. The mixture is brushed on the interior surface of the pre-heated die and the sequence should be repeated until experience shows that a sufficient thickness has been built up. Once coated, the die may be used for many castings before it needs to be treated again.
The casting technique adopted depends to some extent on the nature of the article being cast. In order to avoid turbulence in the molten metal whilst it is filling the mould, it is usual to commence with the die held in a near-horizontal position. The craftsman pours molten pewter from a ladle into the mould, through a 'tedge' or runner and he slowly returns the mould to the vertical position as metal rises in the cavity. Once the mould is upright, feeding is continued for as long as metal will enter the mould. Uniform cooling is promoted by applying wet cloths to the mould, or sometimes even a wet brush. Experience is required to decide on the points
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where cooling should be applied, but often it is at the thickest section of the casting, or where the stream of molten pewter enters the mould, an area of potential overheating. Local cooling prevents contraction cavities from forming at these pojnts. Heavy moulds for large castings may be cooled by lowering them into a tank of water using a motor driven winch; alternatively the mould may be located in a tank which is gradually filled with water. After casting, a 'knocker' consisting of a solid plug of soft metal (such as pewter itself) or hardwood is used to loosen the casting in the mould so that it can be prised out when the halves of the mould are parted; many moulds are fitted with lugs which facilitate handling and opening.
A mould consisting of several parts which is assembled and used to produce the casting on the right. These moulds are often very old but are still used to produce reproduction "antiques".
Turning a pewter casting on a lathe, to remove slight surface imperfections and to achieve a high finish.
The next operation consists of machining the as- cast item on a lathe so as to remove the cast surface of the pewter; in this way slight surface imperfections such as cold shuts remaining from casting are usually removed. The pewter is mounted on an ordinary lathe, similar to that used for turning wood and whilst rotating, the pewterware is worked with various tools, often hand made from steel by the craftsman. Thin layers of metal are removed from the interior and the exterior of the casting and care is taken not to remove excessive amounts of metal, which could weaken the article. When required, a burnished finish can be achieved on the pewter surface using special burnishing tools and wax or soap and water as lubricant. Decorative lines can be scsibed
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on the outer surface whilst the vessel is spinning and fine judgment is required to ensure that such decoration is uniform, particularly when a number of matched items are being produced. Complex designs are often cast in several sections and then joined by soldering. Machining may be carried out before or after assembly, depending on the design of the piece.
Handles, spouts, etc., are cast hollow by a slush casting technique. A hinged book-type mould is held in the gloved hand, molten pewter is ladled in until the mould is full and the mould is then inverted over the melting pot so that metal runs out through the runner, leaving a hollow shell casting. The caster has to judge when sufficient metal has solidified before inverting the mould, so that the shell is strong and yet the casting is relatively light. This not only serves to economise on metal, but also ensures that these appendages are light and therefore do not add considerably to the weight or alter the balance of pewtenware to which they are attached.
Slush cast parts are used on both spun and cast pewtenware. During a long production run of simple shapes, an experienced caster will produce large quantities of castings (rates of over 100 castings per hour have been achieved). Because holding and repeatedly opening the hot mould can be a tedious business, some firms have constructed simple rigs whereby the mould is held rigid and is inverted automatically; opening and closing the mould can be performed by operating a foot treadle on these rigs.
All finished castings are inspected closely for defects. Unacceptable items may be immediately returned to the melting pot, so that there is no material loss, but of course the craftsman's time has been wasted.
Casting in silicone rubber moulds The ease of production of small castings has been greatly increased by the advent of room temperature vulcanising (RTV) rubbers. These are liquids which cure, under the influence of a catalyst, or merely by contact with the atmosphere, into tough, heat resisting elastomers. They are quite stable at the temperature of molten pewter and may be re-used many times. The technique is often used to produce the patterns from which rubber moulds for centrifugal castings are prepared, or as a stage in the production of an art casting by the lost-wax technique.
These RTV silicones are simple to use, provided instructions supplied by the manufacturers are carefully followed. The silicone and the catalyst are weighed and mixed together in the appropriate quantities, using a spatula or a power mixer. The
Slush casting of pewter. Still-molten metal is being paired back out, leaving a solidified shell of metal in contact with the mould walls, which results in a hollow casting.
part to be copied, which may be in wax, wood, plaster or any other material, is cleaned and then coated with the mix, using a fine brush and taking great care to avoid air bubbles which could cause voids and surface blemishes in the mould and hence in the final casting.
Once a thin layer has been built up, the part is located in a box frame, with at least 6 mm clearance between the pattern and the sides of the box and the remainder of the silicone is poured around it, commencing in one corner of the box and allowing the liquid to distribute itself from there, around the model. When the level of the liquid is about half-way up the model, pouring is stopped for a few minutes, to allow the surface to level off. Pouring is resumed until the liquid level is about 1/2 in (13 mm) above the highest point of the model. When the elastomer has set, the model is removed through the base. More frequently a two-part mould is made; this is achieved by embedding the model up to the half-way mark in Plasticine, casting a mould around the exposed half in the manner described and then removing the Plasticine, inverting the model and casting around the other half of the model. These moulds are often backed up with plaster cases which serve to rigidise and reinforce the rubber mould. With these two-part moulds, registration devices should be included in the two halves.
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Casting by the lost-wax method The lost-wax technique is an ancient and traditional method of making single art castings, mainly bronze, but it has also been adapted to making castings in pewter which are larger than those conveniently made by the silicone rubber technique. The starting point is a wax model and the art work may be directly created in wax or else modelled in wood or plaster first and a wax replica then cast using the silicone rubber mould technique described above (in the case of molten wax there would be no such size restriction on this technique as there would be for molten pewter). Feeders and risers are also made in wax and are attached to the wax model by applying a flame to the surfaces which are held in contact, thus partially melting them and forming a bond on ccJoling. The wax is then coated with a layer of a fine refractory slurry, applied using a brush. Dental cement is a suitable material for this purpose. When this surface coating has dried, a layer about 1 /4 in (6 mrn) thick is built up with the same slurry: the surface details of the wax model are now reproduced in this fine cement. The coated model is secured in a box frame and a coarser refractory slurry poured in so as to cover completely the coated metal. When this reinforcing backing has thoroughly dried, the plaster mould is heated in an oven, gently at first to drive off moisture and then a t a higher temperature to melt the wax model which drains out of the inverted mould through the feeder hole. Finally the mould is heated at a high temperature (over 1000°C) to fire the ceramic mould; any remaining traces of wax are burned off at this stage. When cool, the mould is ready for casting and molten pewter is ladled in through the feeder in the usual way. When the pewter has solidified, the mould is broken open to release the casting. It is helpful to colour the original thin skin of dental cement so that it is clear when the casting surface is being approached, during the breaking-up operation. Runners and sprues are detached from the casting, the pewter is thoroughly cleaned free from cement and may be filed and polished to the desired surface finish. This technique has been used to produce many art castings and such unusual items as a large pewter plaque and a Bishop's crozier.
Centrifugal casting Rubber mould centrifugal casting offers the possibility of producing small items quickly and reproducibly even when the parts are of complex shape. In its essentials, the process consists of clamping together the halves of a circular rubber mould which has a central aperture in the top half connected by runners to a number of mould cavities. Whilst this mould is rotating rapidly on a turntable, molten pewter is ladled into the central orifice and is fed by centrifugal force through the channels, into the mould cavities. When the
mould is eventually opened, a radial array of cast parts is obtained, each item being attached by stems to the solidified core. The parts are then easily detached and fettled to the required finish. The rubber moulds may be re-used several hundred times.
The first step in making a rubber mould casting is to create a master pattern of the part to be cast; this should be in brass or some other hard material which will withstand the temperatures and pressures of the subsequent vulcanisation process and which can present a good surface finish and reproduce intricate detail. Pewter itself is sometimes used for making master patterns. A number of these patterns are laid, with their longest axis aligned radially, on a soft, unvulcanised rubber disc about 1 in (25 mm) thick and from 2 f t to 3 f t (60 - 90 cm) in diameter. A second rubber disc with a central aperture is placed on top, so as to make a sandwich. Sometimes sprue formers are inserted between the moulds so as to form feed channels but more ubually these sprues or channels are cut out of the rubber with a sharp knife after vulcanisation. Locating holes are situated near the outer edges of the discs and bolts pass through these so as to ensure accurate registration of the two halves of the mould. The rubber is vulcanised by placing the rqould in a special press held at 165 - 185'C under pressures of about 1/2 tonf/in2 (0.7 kgf/mm2) for 45 to 60 minutes (or as recommended by the rubber supplier). After it is vulcanised the rubber is tough and dimensionally stable, but still flexible enough for small undercuts to be tolerated in the cast parts. The master patterns are now removed, leeving mould cavities which accurately reproduce their contours. The next stage involves cutting feed channels which connect the cavities with the central orifice, as mentioned above. This, as well as the original PO the disc, requi understanding of th to ensure that mol until all the cavities are e path which the m,Olten metal has to follow along the sprues should be minimised. I ak-release holes may ex'tremity of each mdul ed,ge of the disc.
For the casting operation, special centrifugal casting machines have been designed, consisting of a turntable to which the rubber mould assembly in a supporting frame is attached. The unit is encased in a robust steel cabine pouring aperture in the hinged lid, with the central feed hole in the rubber mould via a feed pipe. The turntable is mounted on a steel spindk driven by an electric motor and can rotate a t a controlled speed from 500 to 1000 rpm. The halves of the rubber mould are dusted with french
13
MAKING A LOST WAX CASTING
(a) Burning the last traces of wax out of a plaster mould.
lbl Pouring pewter into the mould, which is conveniently embedded in sand.
(c) Breaking open the mould when the pewter has cooled.
(d) Extracting the pewter casting (in this case a decorative crook for a Bishop's Crozier). The fine plaster next to the casting is convenienlly coloured, to indicate when the pewter casting is being approached in order to avoid damage.
14
Opening a rubber mould, to reveal centrifugally cast pewter figures, connected by spruas to the central pouring point.
chalk to facilitate release of the casting and the mould is then inserted into the supporting frame which sits on the turntable. It is held firmly in position during centrifuging by means of clamps attached to the turntable by pivots which are weighted at one end. During rotation these clamps exert a downward pressure on the mould because the weights are caused to fly outwards by centrifugal force. When the required speed has been reached, the calculated amount of pewter from a melting pot is ladled through the conical aperture. The pewter is typically held at 27OoC, but metal temperature and speed of rotation can be varied so as to achieve optimum filling of the mould. After pouring has finished, spinning is continued for two or three minutes to ensure that all the metal has solidified. The mould is then opened, the casting prised out and the sprues removed with a strong wire cutter. The castings may be finished using files or other tools. For costume jewellery and similar quality products, the castings are often lightly burnished by barrelling with steel balls and they may be electroplated. Provided metal temperatures do not exceed 3OO0C, up to a thousand castings may be made from these rubber moulds; production of a fresh mould from the master patterns, as _ _
described earlier, is relatively simple,
Small decorative or functional parts intended as attachments to other pewterware and including hinges, scrolls and other designs, may be made in this way. Cutlery with decorative pewter handles has been made by locating the steel shaft within the mould cavity of the rubber and casting the handle around it. (The cutting portion of the cutlery may project outside the rim of the mould if necessary).
There is currently great interest being shown in accurately rendered model soldiers, animals and other figures for collectors, war game enthusiasts and for dioramas used in instructional displays. These are easily made in pewter by the centrifugal casting technique. A model is built up by the sculptor, in plasticine or some other suitable modelling material using a wire framework or armature. If the model is in plasticine, it is allowed to age until it is fairly hard. A two-part silicone rubber mould is then prepared (as described earlier in this chapter) and this is used to cast a pewter model, to which final details and adjustments are made by the sculptor. This then constitutes a master pattern for producing rubber
15
moulds for centrifugal casting. The cast figures are often hand painted and experts show great skill in creating verisimilitude in the models, cleverly reproducing textures such as leather or fur. Very attractive chess sets have been made by casting the pieces in pewter and these include special sets made as commemorative ventures.
Pressure die casting Pressure die casting is a well established technique in the engineering industry and in recent years a number of the larger pewter concerns have adapted the technique to the production of small pewterware items. In view of the capital cost of the equipment, the technique is only economically feasible when very large runs of a particular design are required.
In a pressure die casting machine, molten alloy is held in a reservoir and after the die has been closed securely, alloy is delivered to it by means of a pump located in the melt bath. The pump plunger is advanced, to drive the metal quickly through a feeding system, whilst air in the die is allowed to escape through vents. Sufficient alloy is introduced to overflow the die cavities and to fill special overflow wells. Pressure is maintained whilst the metal solidifies. The die is then opened and the casting ejected automatically. To prepare for the next casting the die chamber is cleaned and lubricated; it is then closed and the casting process repeated. This cycle is repeated many times, at short intervals, so that items can be produced quickly and uniformly. Intricate or complex patterns can be reproduced accurately and very little additional finishing of the as-cast parts is required.
16
CHAPTER V - SPINNING
Spinning is a well known metal-forming process by which hollow vessels are produced from a flat starting sheet. However, because of the relative softness of pewter compared with metals like brass and copper, production of spun pewterware requires special techniques and skills of its own.
Spinning takes place on a lathe which is very similar to an ordinary woodworking lathe. A pewter disc is mounted between a shaped mandrel held in the chuck of the lathe and a ’follow chuck’ attached to the tail stock. The lathe spindle consists of a shaft mounted in a pair of bearings and driven via a stepped pulley from an electric motor. In some cases an electric motor with the shaft threaded at one end to take chucks directly may serve as a lathe. It is accurately assembled by allowing the assembly to rotate slowly and then tapping the circumference of the loosely held disc until it is aligned centrally. The follow chuck is then tightened and the disc allowed to rotate at the required speed for spinning; many spinning machines can operate at controlled speeds ranging from about 450 to 1700 rpm. The higher speeds are generally employed, but for large items slower speeds are less likely to cause a thinning effect in certain portions. While the disc is rotating, it is deformed, using special hand-held toois, consisting of steel rods with particular end configurations such as hooks, bulbs or slight curves, mounted into heavy wooden handles of two or three in (8 - 11 cm) diameter for ease of handling. These spinning tools are usually made by the craftsmen themselves or are handed down from father to son. They are not usually available commercially although blacksmiths are still able to make them up. By pivoting the tool over a movable rest associated with the lathe, it is possible to apply pressure to the disc, so that it is deformed over the mandrel, into a cup-like shape. In the early stages the pressure is balanced by a second tool, often made of wood, which is held against the reverse side of the disc. This initial forming operation is known as ’drafting’ and results in a simple cup-like form which follows the shape of the mandrel. The diagram illustrates the operation, the dotted lines showing how the metal is ’pushed’ or rather caused to flow over the mandrel.
In the next stage a more complex form is spun from this simple cup by spinning over a second mandrel of the required configuration. Collapsible mandrels, consisting of several segments, allow profiles to be achieved from which a single solid
mandrel could not afterwards be removed. These mandrels are usually made in hard nylon or some other plastic, and the segments may be dismantled and reassembled around the shaft of the lathe several times at intervals during the spinning process to ensure that join marks do not become impressed into the pewter. Before the advent of collapsible mandrels, vessels with a narrow section had to be ‘spun on air’ (i.e. without inserting any mandrel). The uniformity of the spun profile had to be checked at intervals, using a curved template and later calipers for precise checking, but it was still extremely difficult to produce a uniform contour without distortion and to maintain a satisfactory distribution of wall thickness.
When a mandrel is used, metal is urged to follow its contours by applying the spinning tool, counter pressure often being exerted on the diametrically opposite side of the vessel by pressing with a cloth held in the hand. Once the appropriate shape has been attained, the tool is used with a kind of ironing action which distributes the metal so that thicker walls are obtained where greatest strength is required. A skilled spinner can produce a tankard or goblet which appears, on inspection of the rim, to be made up of a thicker gauge than the starting sheet.
Flatware, such as plates or bases for tankards, may also be made by spinning, when the only operation may be a simple turning over of the edge to make a flange (in the case of bases) or a simple profiling over a flat mandrel (in the case of plates). Some tankards have a glass insert in the base and this may be seamed into place by spinning. When metal has to be trimmed away to make an even edge, this is achieved by deft touches with a metal cutting edge. Incised lines are scribed on the surface whilst spinning and again care is needed to produce uniform pressure and an even application of the scribing tool.
In many cases, the first drafting operation is avoided by making the starting point a cylinder, which has been formed by rolling metal sheet into a tube and soldering the side seam. This is done for cheaper tankards and also when very large vessels are required for which a starting disc would have too great a diameter to be accommodated on a lathe. (However, in the U.S.A. it is not customary to make hollow-ware in this manner; spun pewterware produced there always starts from pewter sheet, and does not have a soldered side seam).
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A shaped mandrel is inserted in the formed visible evidence of the soldered side seam and the cylinder and a final profile arrived at, as described addition of incised lines by way of decoration. previously. In the case of cheaper, straight-sided Bases for these tankards are spun separately and tankards, the only operations may be flanging of are attached by soldering. (The soldering process the ends, pressure of the spinning tool to remove is discussed in greater detail in Chapter VII).
n blank
follow block
.~
- \ \ \
Principles of spinning pewter sheet.
Spinning a pewter dish from flat sheet. Note the wooden tool held in the craftsman's left hand, wh& is used to 'back up' the pressure exerted with the metal spinning tool.
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The last stage m the production of spun tankards is high speed polishing.
Buffing and polishing Once the pewterware has been formed, the quality of the metal is brought out by a series of buffing and polishing operations. Some of these are undertaken before handles, etc., are soldered into place as they would obviously hamper an all- over buffing. However, final polishing takes place on the complete item.
B~uffing takes place against a mop, consisting of strips of strong cloth such as calico wrapped around a spindle; this is attached to an electric motor in such a way that it can rotate rapidly on a horizontal axis. The surface of the pewter is lightly pressed against the rotating mop and a suitable polishing medium is applied. The purpose of buffing is to remove from the surface traces of tool marks or other imperfections. The abrasive medium should be suitable for achieving this purpose without scratching or otherwise damaging the pewterware. Often sand moistened with linseed oil and sometimes containing pumice in' addition, is used; adequate ventilation must be provided and the operator should wear a face mask to avoid ingestion of sand. The.mop or buffing wheel is lightly touched with a grease stick while it is rotating, to provide lubrication and then sand medium is introduced manually between the mop and the workpiece. 'Underhand' polishing is usually preferred; i.e. the wheel rotates towards
and down from the operator and the pewter is applied below the axis of the wheel. The sand is located in a pit situated underneath the buffing wheel, and as it falls it can be scooped up and re- used. Proprietary greaseless compounds are available, usually in bar form. These may be used in place of sand and they are formulated from fast- cutting abrasives combined with a lubricating binder to produce a tenacious coating on the buffing wheel surface. They are applied by holding the stick against the rotating mop for a second or two. Before using a new mop, an extra application of compound should be made and a few seconds allowed for it to dry on the mop. Speeds of up to 1800 rpm may be used for buffing. When a satin finish is required on pewterware, a coarser abrasive is used which virtually has a 'scratch brushing' effect; these items are not then normally polished further.
The pewterware is next washed, to remove all traces of sand and grease and allowed to dry in a hot air oven. Other parts may be soldered into position at this stage. Final polishing is performed using softer mops which are first lightly greased; jeweller's rouge (litharge), made into a paste with water or methylated spirits, may be used as a polishing medium when a highly reflective finish is to be produced on the pewterware.
19
SPINNING OF PEWTER
(a) Drafting the pewter sheet over a formed chuck.
(b) Trimming &ps with a metal tool, whilst the vessel is rotating.
(c) Assembling a 'split chuck'
produce vessels with MWW
sections, the chuck being dismantled for removal after spinning.
which can be used to
(d) Forming the drafted pewter vessel over the chuck so that it takes up the required profile.
CHAPTER VI 9 OTHER M€TAL WORKING PROCESSES
Pewter sheet for making hollow-ware is now usually supplied as blanks of the particular shape required, i.e. as a disc for spinning seamless vessels and as a tapered sheet for producing side- seamed tankards. This supply of readymade blanks lends itself to the large scale production of pewterware. When a relatively small number of items are required or blanks of unusual configuration are needed, these can be cut out manually, using templates and a sharp knife or shears, since pewter is a relatively soft metal. The
blanks for making side-seamed vessels are passed a number of times through specially designed rollers which cause them to curl into cylindrical forms. The subsequent procedure for making up these tankards has been discussed elsewhere.
A rather similar technique has been used to fabricate organ pipes from rolled pewter sheet. The sheet is marked out using templates and then cut to shape. The cylindrical body is formed by hand around a suitable mandrel, by beating with a
Merking out a pewter blank, using a template of the required shape. Pewter is easily cut, using shears or stout scissors.
21
hardwood tool. Masking size is spread around the joint area and a V-channel is cut down the length of the seam and masking size scraped away at the joint. Solder is applied to the side seam, using a fairly cool soldering iron and the seam is made slowly but steadily. It should be noted that for most soldering operations involving pewter, a soldering iron is not used because of the danger of the hot soldering bit burning through the pewter sheet if it should make more than very brief contact with the surface.
A traditional method of making plates and trays consists of cold forming pewter sheet into a metal or wooden mould. This may be achieved by hammering the sheet, using special wooden or plastic tipped mallets which do not mark the surface, so as to force it to follow the contours of the mould.
In the modern pewter industry, shallow vessels may be produced by mechanically pressing the sheet into metal dies. Bodies of tankards and the surfaces of dishes may be hammered with special metal planishing hammers which produce regular indentations in the pewter. These serve to strengthen the pewterware and produce an attractive finish. The technique requires much skill and is necessarily a slow process. Today, cheaper and faster mechanical techniques are used to produce a somewhat similar effect on lower-cost mass-produced pewterware. The pewter sheet is placed in contact with a special die bearing the indented pattern (or other decorative designs) and the two passed through rollers. The sheet is then formed into the finished article in the pre- decorated condition.
Other metalworking processes, suitable to the hobbyist, are discussed in Chapter IX; engraving on pewter is covered under 'Decorative Finishes' in Chapter VIII.
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,
CHAPTER VII - SOLDERiNG OF PEWTER
The standard method of joining pewter components is by soft soldering. A strip of the pewter itself, or a tin-based low-melting alloy, is used as filler metal and under the action of heat this melts, "wets" the surfaces to be joined and by capillary action is drawn into the gap between them. The surfaces to be joined must be cleaned and are preferably scraped to expose fresh metal just before soldering.
A gas/air torch is a convenient form of heating and this is widely used in the pewter industry for soldering operations. Considerable care is needed to avoid overheating portions or even melting a hole in the metal, due to the small difference in melting point between pewter and solder. However, the torch can produce a fine jet of flame which can be directsd accurately to the point where it is needed; practice is required in the best technique for using it, The torch is often hooked on the edge of the operator's work bench or supported on a jig and to avoid accidental burns, the flame should be extinguished between
soldering operations or at least adjusted to a cooler, luminous flame which is easily seen. As a simple alternative to the gadair torch for small scale precise work, a mouth operated blowpipe may be used to direct precisely a jet of flame from a bunsen burner. Occasionally hot air blowers are utilised, the air temperature being adjusted so as to exceed the liquidus of the solder alloy. There is less risk of melting the pewter itself with this method, but the rate of heating is much slower than with a flame.
Solder may be used as strip or as wire and should be dipped in a liquid flux just before application. This flux serves to remove oxides or other thin films of contaminants from the surfaces to be joined and hence promotes wetting. Suitable fluxes include glycerine containing some hydrochlor]c acid or a 25% solution of rosin in alcohol. Sometimes flux cored solder wire is used which has a solid core of flux located inside the solder wire. This flux core may be rosin-based or of a mild acid type.
Attaching a handle to a pewter tankard, using solder wire and a gdair torch. Note the turntable on which the vessel is placed for ease of handling.
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Commonly used solder alloys are shown in the Table. Pewter itself is also used, for soldering the side seams on tankards and for other soldering applications where joints might conceivably come into contact with food or drink.
Tin Lead
63" 37"
60 40
70 30
SOLDER ALLOYS FOR JOINING PEWTER
OF OC OF OC
361 183 361 183
361 183 372 190
361 183 378 192
Alloy Composition
*This alloy is a eutectic, i.e. it melts at one unique temperature and not over a range of temperature.
Quantities of bismuth may be added when a lower melting point solder is required. Tin-lead cad- mium alloys were sometimes also used for this purpose but are not recommended and are little used now, partly on the grounds of toxicity of cadmium-containing materials. A 42% tin - 58% bismuth alloy is however sometimes used as a non-toxic solder for pewterware.
Typical soldering procedures used to attach various components to a pewter vessel are discussed in the following.
Attaching bases to tankards The pewter bases are stacked on a wooden turntable, one on top of the other, to a height of a foot or so (about 30 cm). They are pre-heated by gently playing a torch flame over them whilst they are made to rotate on the turntable. When the requisite temperature has been reached, the mass of the stacked bases acts as a heat reservoir to maintain this temperature during soldering of the individual bases. The body of a tankard is placed over the topmost base, solder wire is dipped in flux and then applied to the joint between base and tankard whilst the assembly slowly revolves. By means of a torch flame, the solder is melted and care is needed to regulate the heat flow so as to ensure a small steady supply of solder. This fills the capillary space between the base and the tankard wall and produces a secure, leak-proof joint. On completion of soldering, water is poured into the tankard and this serves to cool the joint as well as providing a test of water tightness. The tankard with its base attached is then removed and a fresh tankard body is placed over the next base on the stack. In , a quantity of bases may be soldered quickly and reproducibly.
Joining side-seamed tankards The formed cylinder of pewter sheet which is to become a tankard body is held firmly so that the edges making up the side seam are just touching. These edges are cleaned by filing or lightly scraping with a knife and then heat is applied along the length of the seam from a fixed gadair torch. The solder stick or wire is dipped in an alcohol/rosin flux and applied to the ends of the seam and to a point near the middle. This 'spot' soldering maintains the configuration of the cylinder whilst heat continues to be applied along the length of the seam. The stick is then dragged sideways or 'wiped' along the length of the seam. Solder flows into the joint gap and right up to the interior surface of the vessel. When cool, the cylinder is placed over an iron mandrel and hammered so as to beat down the raised seam. A skilled craftsman can make the joint almost invisible a t this stage; final traces are removed during buffing and polishing operations. In any case, handles are usually sited over the seam area and serve to mask further any slight evidence of a joint.
An alternative procedure sometimes adopted consists of mechanically constraining the curled cylinder of pewter so that the edges remain touching and facing downward, fluxing and placing lengths of solder wire along the seam on the inside surface, When a torch flame is directed gently over the seam area. these pieces of solder melt and fill the joint.
Soldering a spout on a coffee pot The position of the spout is first decided upon and marked upon the surface of the pot (if there is a side seam, the spout or the handle will be located there). The spout is pressed firmly against the cylinder and its contour is traced on the surface. Areas to be soldered are scraped clean and a hole
tre of the spout area. Starting rea under the spout is cut out, aw blade. Flux is applied and
the spout is held in position. Heat is applied from a fixed gas/air torch and solder wire is wiped along the joint so that molten solder flows into and fills the gap between the surfaces. Handles and other
be soldered in position in a similar
A 'spot welding' technique has been used for precise soldering of small parts as when attaching
ewter figures. The figure is e of a battery and by lightly to be joined with a small
nected to the other pole, akeS place and the surfaces
melted, forming a strong bond on
24
SOLDERING A SIDE SEAM
(a) The sheet previously cut to shapa, is folded into a tapered cylinder and held together for application of solder.
(b) Solder wire is applied, using a fixed gaslair torch for heating; initially a number of 'spot joints' are made to hold the cylinder in place.
(c) The solder wire is gradually wiped down the seam so as to make a soldered side seam.
(d) The completed side seam. This is afterwards hammered flat with the vessel held over a metal mandrel.
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CHAPTER Vlll - DECORATIVE FINISHES
The appearance of pewter can be enlivened and enriched by applying surface decoration. A selection of finishes is shown here.
There are a number of ways of enhancing the decorative appearance of pewter and these range from finishes imparted mechanically (by buffing and polishing) to chemical treatments and engraving and etching.
In addition to the standard finishes such as highly reflective and duller satin surfaces, darkening treatments can be applied to pewter to simulate the appearance of the antique material. Pewter from earlier periods tarnished easily, due partly to the presence of considerable quantities of lead. This 'antique look' is held to be desirable by many devotees of pewter and whilst modern pewter remains bright in a normal atmosphere, chemical treatments have been devised which will darken the surface of the metal permanently and to a controlled degree. It should be remembered that this is only a thin surface film and that any polishing or abrasion is likely to remove it, exposing the bright surface underneath.
Chemical treatments A number of solutions have been developed for producing coloration on pewter surfaces. The work must be free from grease and oxide films and this can be ensured by lightly rubbing the surface with a paste of magnesium oxide and water and by rinsing before immersion in the colouring solution.
NOTE Some of these solutions contain poisonous or corrosive substances and care must be taken in handling them. Rubber gloves and eye protectors should be worn by the operator and spillages should be diluted with copious amounts of water and mopped up. In preparing solutions, particular care is needed when diluting concentrated acids; acid should be added slowly to water, with stirring to dissipate heat, and water should never be aaded to the concentrated acid.
26
Blue-black patina 2.5 g copper sulphate 50 ml nitric acid (concentrated) 950 ml water
Brownish-black patina 80 g arsenious oxide 40 g copper sulphate
450 ml hydrochloric acid (concentrated) 500 ml water.
5 g ammonium chloride
Grey to black patina 100 ml sulphuric acid (concentrated)
900 ml water. 15 ml nitric acid (concentrated)
Here, pewter vessels are being given a chemical darkening treatment; after rinsing they asre allowed to dry. The dark colour achieved is permanent.
The intensity of the colour obtained from treatment in all these solutions is time-dependent and immersion times can vary from about 30 seconds to about 4 minutes, depending on the degree of darkening desired. Treated parts should be water washed and allowed to dry, perhaps in a warm cabinet. The coating may be relieved by a light buffing which allows highlights to gleam through here and there. The patinas, obtained
from the chemical treatments are sometimes coated with a wax polish, or sprayed with lacquer to ensure a greater degree of permanence. This is particularly the case with costume jewellery.
Electrolytic processes have been used for colouring pewter and an adherent coating can be achieved in one or two minutes. The pewter item is immersed in the treatment bath and made the cathode; a steel anode is also immersed in the bath and a current is passed through the solution. Operating details can be obtained from suppliers of proprietary processes, such as ‘Enquist Electroblack’, available from The Enquist Chemical Co. Inc., 100 Varick Avenue, Brooklyn, N.Y. 11237, U.S.A. One suitable process is described in the International Tin Research Institute Publication No. 504.
Engraved designs The interest of fairly commonplace pewterware, such as straight-sided tankards, is very often heightened by applying engraved or etched decoration. Hand engraving is now restricted to the higher priced end of the pewterware market, since the time of a skilled engraver is required in this work. The craftsman transfers a selected design, often of his own composition, to the surface of the pewter vessel, either by pencilling over Plasticine or by dusting with chalk. The metal is then engraved directly through this design using special tools. One error here and the pewterware is spoiled since there is no way of erasing mistakes. The tools, known by such picturesque names as ’shavers’, ’spotters’, ’gravers‘ and ‘wrigglers’, are made by the individual craftsman by honing down mild steel rod on a special stone. The engraving technique takes a great deal of practice to master. Basically the craftsman tends to push the tool against the pewter surface, rather than dragging it along.
Mechanical engraving To cope with the production rates required in today’s pewter industry, modifications of the engraving process have been introduced. A pantograph arrangement may be utilised whereby a pointer, guided around the contours of a master pattern, controls an engraving needle at the other end of the arm, which cuts into the surface of a rigidly supported pewter vessel, tracing the master pattern on the pewterware.
Although such engraved works do not bear the individual touch of the craftsman’s hand, the technique does allow simple designs to be applied rapidly and reproducibly to pewterware. A more widely used procedure consists of rolling a pewter blank in contact with a patterned die, so that the pattern is in fact pressed rather than cut, into the surface. Quite complex detail or lettering can be reproduced by this method.
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Etching of pewter Another art technique which has been adapted to pewter decoration is etching. A modification of the silk screen etching technique, so widely used in printing, is used to produce pictures and lettering on pewter surfaces. A mask is placed over the pewter sheet and acid is allowed to pass through the unmasked areas on to the pewter surface. In this way, the pewter is selectively etched or darkened and a design is faithfully transferred to the surface.
This process and the mechanical engraving technique are only applicable to flat sheet, and the decorated sheet is subsequently made up into pewter items. For art works, where achievement is more important than cost of production and the pressures of mass production do not apply, engraving and etching represent exciting ways of enriching the surface. There are numerous artist- craftsmen throughout the world who are producing beautiful designs in pewter for use as wall plaques or table tops. Pewter presents a very suitable surface for such work and the subtle lustre of the metal adds a further dimension to the finished work. A procedure followed by one such artist in Australia is described below.
Heavy gauge pewter sheet is coated with bees- wax, darkened with a small quantity of asphaltum. A drawing is outlined on thin paper and then traced on to this wax. Using a suitable scribing tool, the wax is selectively removed from the traced lines. The whole is then immersed in dilute nitric acid which, as well as dissolving away portions of metal a t exposed pewter surfaces, imparts a grey-to-black patina to the etched line, providing a strong outline. The acid strength determines the nature of the etching; sharper vertical edges result from stronger solutions, whilst softer, rounded edges are produced by more dilute acid. After etching, the wax is removed with a suitable solvent and the pewter surface is finished by hand. When mounted on a timber base, these etchings make attractive wall hangings.
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CHAPTER IX 9 PEWTER FOR THE HOBBYIST
Pewter makes a very suitable craft material, being clean and pleasant to handle. It is soft and can be folded easily; it can be modelled in relief, have holes punched in it and in the thicknesses normally employed is capable of being cut with strong household scissors or with a knife. Although some practice is required for soldering pewter, it is easily glued to many materials and
ent for much craft -work. offers scope to the mere
I I as to the more advanced student, artist it can be a stimulating new
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The basic equipment consists of a working surface for relief work, which may be board covered with a layer of felt or linoleum; hardwood
and stakes; and suitable hand tools for , scribing, filing, cutting and hammering. castings are to be attempted, a melting be required (a saucepan on a gas ring
would be adequate) and a supply of mould making materiais (plaster or silicone rubber). Fortunately, today there are many well stocked craft shops where most of these items can be purchased;
improvised with a little ingenuity. ewter ingots and sheet can be
from commercial manufacturers. pliers will probably stipulate a minimum h they will consider. There is scope schools and colleges which have
ing courses to purchase bulk supplies Id be made available to students a t a
s the simplest techniques for a beginner relief work, in which the surface of the
metql is raised by applying gentle pressure on the reverse side. Wooden tools such as those used for Plasticine modelling may be utilised for working the metal or thick wooden knitting needles may be cut down and sanded to particular end configurations; even a glass rod may be used for simple modelling.
First practice attempts should be made with a small piece of scrap pewter sheet. The piece is laid down on a felt covered"b"oard and a design lightly traced on the surface by laying a pencil drawing over it and going over the lines firmly with a wooden scribe. For first attempts, a relatively simple design should be used. The drawing is then removed and slightly heavier pressure applied to selected portions; on reversing the sheet these parts will be seen to be raised somewhat. With
practice, the degree of pressure needed to produce different amounts of relief can be established. Wider raised areas can be achieved by using blunter tools with a thicker end. When a satisfactory relief design has been achieved, the deprebsions occurring on the under side may be
backing. Such designs can be purely
attractive effects.
Simpie designs can be achieved merely by laying a cardboard stencil on a pewter sheet and hammering it into the surface of the pewter. If a press is available, the pewter plus stencil may be placed in this in order to achieve the same indentation more uniformly. When the stencil is peeled away, its shape is impressed into the pewter surface. This may then be etched by placing small crystals of copper sulphate on the indented surface and applying, with a small
Relief patterns can ba produced on pewter sheet by placing it on a soft surface and applying pressure with a special tool on the reverse side. Here, final adjustments are being made to the raised design.
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camel-hair brush, a solution of 50% hydrochloric acid or nitric acid, containing some copper sulphate. (Caution should be exercised in using these acids, which can cause severe burns if left in contact with the skin. Spillages should be mopped up with copious amounts of water). This mixture blackens the surface and the presence of the solid crystals ensures a patterned or mottled finish. After about one minute, the solution and crystals are washed off, the plaque is dried and may, if desired, be polished, using a proprietary metal polish.
Forming in hardwood moulds Slightly more advanced techniques can be used in making ash trays, dishes or shallow bowls by flow forming. For this purpose hardwood moulds are needed. Simple moulds can be carved by hand and can then be used many times: if a wood turning lathe is available, more elaborate moulds can be made.
In order to make a simple pewter bowl, a disc of pewter about 10 in (25 cm) in diameter is cut from sheet, taking care to remove any sharp snippets of metal and filing down rough edges. This sheet is then placed in a shallow mould with an inside diameter of at least 12 in (30 cm). Using a wooden or a fibre mallet, the largest available, the edge of the disc is raised by pounding around the outside perimeter with overlapping strokes about 3/4 in (20 mm) inside the edge of the disc, the outer edge of the sheet being supported against the mould surface. A mallet is also used to press the
disc gently into the mould. A delicate touch will prove more effective than hitting the metal too hard. Once the pewter is set nicely into the 12 in mould, it is transferred to a 9 in (22 cm) diameter mould and the process is repeated. In this manner, the curvature of the bowl is gradually built up, using a series of moulds of decreasing diameter. If a flat base is required, then the starting disc should have a 3 in (8 cm) diameter circle inscribed on it at the centre and this area is kept clear of the mallet. To adjust the circularity of this base after forming the bowl, a 3 in wooden disc may be set in place inside the bowl, which is placed on a sand bag, or other yielding surface. Hitting the disc firmly with the mallet will impress a regular circular indentation into the base.
An oval tray can be made by inscribing two ellipses on a pewter sheet, one ellipse inside the other, leaving about a 1 in (25 mm) border. The larger ellipse is cut out and this border is then turned up by hammering against a hardwood stake held in a vice, gradually working around the edge of the sheet.
Pewter jewellery Pewter jewellery has an attractive, expensive look and is very popular today. A variety of items can be made by the home craftsman, in fact much of the jewellery seen in the shops is made on this basis. Some simple ideas are presented here, which the enthusiastic amateur can take up and develop further.
Effective designs can be achieved on pewter by impressing a stencil into the surface and then applying special chemical treatments.
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A 'leaf brooch' can be made by transferring a leaf design to pewter sheet (perhaps using a template if a number of similar articles are to be produced) and the shape cut out, using stout scissors or shears. The edges should be carefully trimmed
1 and rounded by hammering and filing. The veins , of the leaf are then incised into the metal with a 'suitable scriber and the surface of the leaf is textured by hammering all over. The finished item should be cleaned in petroleum spirit and perhaps given a coat of lacquer. Safety catches can be attached to the reverse of the brooch using a strong adhesive.
Attractive bracelets can be made by cutting out a strip of pewter, as wide as the intended bracelet and tapering towards the ends, these ends being rounded in profile. The cut edges should be filed and hammered to remove any sharp portions. The strip is then curled around a cylindrical mandrel and a textured surface is imparted by beating with a hammer having a serrated hitting surface. (This may be achieved by scoring the hammer surface with a file). A second hammer is used to bevel the outer regions of the bracelet which have not been textured and the object is 'laid down' (so as to
keep its curvature) using a rubber or plastic-faced hammer which does not impart to the metal the "spring-back" associated with the use of a metal- faced hammer. Other methods of decoration may be used; gemstones may be attached to the surface, using a strong adhesive, the pewter may be engraved, or it may be 'hand scratched'. This last process can be achieved by laying a metal stencil on the surface of the strip before it is curled, and rapidly running a steel tool, freehand, in a random fashion, over the area exposed within the stencil. All items should be lacquered before use, to preserve the surface finish and appearance. Small pendants can also be made by casting in silicone rubber moulds, as described in Chapter VII.
Simple castings Plaster of paris is a convenient material for making simple rioulds and quite effective cast pewter designs can be made without too much difficulty. The part to be copied is placed in a holding box and plaster slurry is carefully poured in until it reaches half-way up the model. When this has set, the top surface of the plaster is swabbed with hot soapy water and this is allowed to dry.
Texturing a pewter bracelet by striking it with a metal hammer bearing a specially roughened surface. The bracelet is supported over a metal mandrel.
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Pouring is recommenced until the pattern is completely covered with plaster to a depth of at least 1 /2 in (12 mm). When the second half of the mould has set, the two halves may be separated a t the parting surface. The mould should be thoroughly dried but overheating, which could cause the mould to distort or crack, should be avoided. A channel through which molten pewter can be poured, is then cut into the two halves of the mould, tapering from the widest point a t the outside of the mould, to a narrow portion at the mould cavity. A mould wash of colloidal graphite should be painted on the surfaces of the mould cavity (or these surfaces may be blackened over a candle flame). Before casting, the two halves of the mould are securely clamped together and provision of locating pins and corresponding holes when making the original mould will ensure that the two halves are accurately registered. Pewter for the casting operation may be melted in a saucepan on a gas ring; off-cuts and other scraps frcm sheet-forming processes may be melted down for this purpose. Any dross on the surface of the molten pewter should be skimmed off and the metal is then ladled into the mould. Using plaster moulds, no undercut sections are possible unless the mould is subsequently to be broken. However, by using RTV silicones for mould making, as described in Chapter VII, undercuts are possible.
More advanced techniques of soldering, metal forming and casting are probably best studied under a qualified supervisor and there is a good case for the basic techniques of pewter crafting being incorporated into the metalworking syllabus at schools and colleges. Pewter should lend itself well to classroom methods. Moreover, there is always a need for craftsmen in the pewter industry, so that a basic training in the skills of working with pewter would stand the student in good stead as regards a future career, or a t least instil in him an appreciation of the craftsmanship involved in making the items seen in the shop.
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CHAPTER X 9 ELEMENTS OF PEWTER DESIGN
A consideration of traditional elements plays a large part in the design of pewterware and indeed this aspect is a major selling point. Certainly, many traditional designs are elegant and show a great respect for the advantages and the limitations of pewter. Much modern pewterware is based on original older designs, the craftsman adding his own personal contribution in bringing his work into the contemporary idiom. An interesting feature of modern pewtenware is the influence exerted by national preferences. Thus German pewter tends to be heavy, with elaborate ornamentation, Scandinavian products are simpler and more functional, whilst Japanese and Malaysian pewterware have the subtlety and delicacy associated with the East.
The earliest pewterware was probably entirely functional; before earthenware pottery and porcelain had been developed, pewter represented a convenient material for making plates, bowls and drinking vessels. The survival of much of this pewter in a relatively intact state shows that the design capabilities of the material were well understood. Large sections of thin metal should not be left unsupported, particularly if they are to bear loads, as in the case of trays. Vessels to hold hot liquid should be designed in such a way that adequate thickness is provided a t vulnerable areas where distortion might otherwise occur. Although hot tea or coffee can be
dispensed perfectly safely from a pewter pot, liquids should not be heated in such a vessel, for example on a gas ring, since the low-melting metal would soften and distort. Modern pewter does not blacken or tarnish, but when deciding on a surface finish, the intended end use must be taken into consideration; thus for a tankard or goblet which will be much used, a satin finish, less prone to finger marking might be the most suitable. However, if the chief function is to be a decorative ornament, then a highly reflective finish may be considered more eye-catching.
Modern pewter contains no added lead and is quite safe to use in contact with food and drink. Its appearance is easily maintained, a wash in warm soapy water followed by rinsing and drying, being sufficient to remove any accrued dirt or grease. The neutral' colour of pewter and its surface appeal make it suitable for use in modern interior decoration schemes and the wide range of finishes and textures which can be achieved further widen its decorative scope. Pewter can be combined with other materials to good effect; thus heat conduction to the handle of a coffee pot can be reduced by adding a cane or wooden handle to the pewter vessel. Used in coniunction with a coloured lampshade, pewter makes an attractive table lamp; glass and pewter unite to good effect in many items.
Modern candlestick designs; the clean simple lines are typical of much British pewter.
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Pewter drinking vessels Perhaps the item most closely connected with pewter in the mind of the public is the tankard. This developed from the beaker, which first appeared at the end of the 16th Century and which did not have a handle; tankards with handles and lids first appeared around the mid - 17th Century. These were flat topped but were soon followed by tankards with domed lids. After 1800, most tankards, in Britain at least, did not have covers. There are traditional tankards which are tulip-shaped, thistle-shaped and barrel- shaped; there is also the gracefully curved Georgian seamless tankard, so popular today.
In addition to tankards there are measures for ale and wine, one of the best known being the tappit hen, which has a capacity of 3 imperial pints. This lidded and lipped vessel is still a favourite amongst pewter manufacturers; another popular item is the 'Irish Haystack' which rises in a domed 'haystack' configuration from a lower, straight-sided section. Traditional goblets and pitchers and the two- handled 'loving cup' are other favourites with the public.
These antique designs still influence modern pewterware production and in fact, facsimile versions of the original styles are 'best sellers' in the pewter industry. In this connection, old casting moulds, perhaps centuries old, are still
used on occasion and pewterware cast in them bears on its surface the original touchmarks and blemishes. The adoption of this practice raises the interesting question as to whether or not these items are 'antiques', as they are cast in the original mou Ids. Many designers take these traditional pewter vessels as a point of departure for newer products, modifying and amending them so as to imprint their own individuality on an established style. In some cases, silverware designs have been interpreted in pewter.
Pewter around the world The appearance in the market place of pewter from many countries affords the potential customer a wider choice than ever before. One of the most active countries in terms of pewter manufacture is Germany and the public there are able to purchase a wide range of products, both utilitarian and decorative. Table lamps, candlesticks, wall hangings, clocks, lighters, ash trays and pipe racks as well as a whole variety of tankards, goblets, beakers, bowls and plates are catalogue items for many manufacturers. A popular feature comprises a set of wooden shelves which display pewter spoons, plates, steins and goblets, the whole making an attractive wall decoration. One also finds many designs in which an adventurous combination of pewter with glass or wood has been undertaken.
A hanging wall clock, showing the ornate decoration characteristic of German pewter.
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It is commonly accepted that the recent re- awakening of interest in pewter had its origins in the innovations in design which were made by the Scandinavian craftsmen in. the 1920's. Today Scandinavian pewter is still noted for its style, particularly in the field of costume jewellery. French and Belgian pewter items rely heavily on long-established styles and they are mainly made by casting techniques. However, there are a number of artist-craftsmen who turn out individual designs of striking originality, using the ancient technique of beating with a hammer. One firm in Belgium employs sand casting methods to produce sculptures and other works of art in pewter. Although slower than conventional metal mould casting, an exceptional degree of finish is obtained in the pewter giving a high quality product.
North America is the world's major market for pewter and affords invaluable export outlets for the pewterware manufacturers of Europe. In addition it has its own flourishing pewter industry, dating back to the Colonial period a t the middle of the 17th Century. Many items in the manufacturers' inventories date back to this
period for their origins, for example the Paul Revere bowl, the Copeland spoon and the Jefferson cup. There are specialist workshops in the U.S.A. which repair antique pewter items which are highly prized by collectors. Most U.S. pewter is produced by spinning; in addition, many works are made by hand crafting methods and there are some noted North American artist- designers working in pewter.
Pewter from Malaysia is now appearing on the European scene and this industry, set up to take advantage of the locally-produced tin metal, is flourishing. Casting is the method of manufacture and an attractive finish is obtained with the pewter alloy, which has a very high (97%) tin content. Many designs carry engravings of Malaysian motifs.
The continent of Australia, unlike North America, was developed at a time when pewter was no longer in vogue as a material for household materials and hence there is no long tradition of pewter production. However, there are now a number of firms manufacturing pewter in that continent and no doubt a characteristic
Malaysian pewterware has an appeal of its own, as can be seen in these cast items.
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'Australian style' will emerge in due course. Another newcomer to the pewter scene is Japan. Japanese pewterware is characterised by extreme delicacy and degree of finish astonishing in hand- made items. The colours and textures used for decoration, too, give the pewterware a unique appearance. Typical products include sake sets (comprising a jug and small drinking vessels), tea sets, flower vases, cake dishes and liquor goblets.
In 1955 the International Tin Research Institute organised an international exhibition called "Pewter of Today" at which a representative collection of pewter from many countries could be seen.
The exhibition opened in London, in a major department store and subsequently was staged in many other cities in Europe and the U.S.A. It was instrumental in reviving interest in pewterware, which had been in abeyance over the period of World War II. A permanent, international display of pewterware is maintained at the Institute's Headquarters in Perivale, London, and this shows examples of the best in modern pewter. There is a strong interest these days in the craft aspect of pewter, possibly as a reaction against the machine age. In 1976, London's Victoria and Albert Museum held an exhibition entitled "Metalwork in the Making" at which visitors were able to see craftsmen making pewter on equipment which had been set up in the museum and could also purchase examples of the work.
In 1978 a Silver Jubilee Design Competition was sponsored by the Worshipful Company of Pewterers in London and many of the entries displayed an originality which bodes well for the future of the pewter industry. The Institute recently produced a colour booklet on "Modern Pewter" which contains numerous illustrations of the pewterware currently being produced throughout the world. A 16 mm film with sound, called "Pewter, an Ageless Metal" is freely available on loan from the Institute or its Tin Information Centres. This is a general interest film and shows many of the manufacturing techniques described in this book, as well as illustrating the many kinds of pewterware available to the public.
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The Institute wishes to thank its friends in the pewter industry for their assistance in the compilation of this book. In particular, the following companies who provided assistance in producing the illustrations: ~
Culf and Ka y (Sheffield) Ltd., Sheffield, England.
James Dixon and Sons Ltd., Sheffield, England.
Englefields (London) Ltd., London, England.
Fashionware Products (Sheffield), Sheffield, England.
Pipecraft, Norfolk, England.
PMC (Sheffield) Ltd., Sheffield, England.
N. Saunders (Metal Products) Ltd., Twickenham, England.
Selangor Pewter Co. Sdn. Bhd., Kuala Lumpur, Malaysia.
James Smellie Pewter, Birmingham, England.
The Walden Spoon, Walden, New York, U.S.A.
Wardle and Matthews L td., Sheffield, England.
Lorenz Weber and Co. L td., Frondenberg, W. Germany.
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