the goldsmiths’ company TECHNICAL BULLETINtechnical-journal.thegoldsmiths.co.uk/wp-content/uploads/...reputation of the Goldsmiths’ Company in jewellery manufacturing technology

t h e g o l d s m i t h s ’ c o m p a n y

TECHNICAL BULLETINIssue 5 April 2007 Published by: The Technology & Training Department

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1. mATeriAls mATTerDiscolouration of Carat Gold Jewellery ...............................................................3The Hardness of Jewellery Alloys. Why is it Important? ...............................6

2. inVesTinG in TeCHnoloGYB&N Rings Limited ......................................................................................................10

3. neW TeCHnoloGY FoCUsLatest Product News..................................................................................................12

4. TeCHniCAl sUrGerYAsk the Experts ............................................................................................................13

5. rePorTInternational Santa Fe Symposium 2006 .......................................................14

6. HAllmArKinG UPDATe British Hallmarking Law Amendments ...............................................................18

7. resoUrCes AnD oPPorTUniTies The Jewellery Sector Investment Plan ...............................................................20Industry Training .........................................................................................................22Project Announcement: New Sterling Silver Alloys .....................................23

8. CAlenDAr oF eVenTs ......................................................................... 24

T he death of Peter Gainsbury on Monday 22 January 2007 at the age of 84 is noted with considerable sadness. Peter was not

only a former senior officer of the Company but also a Liveryman and did much to establish the reputation of the Goldsmiths’ Company in jewellery manufacturing technology.

Before Peter Gainsbury joined the Company, the main effort had been directed primarily towards the ‘artist craftsman’ aspect of the trade and it was Peter who was given the brief to widen its influence. He established contact with the manufacturing trade, a policy that remains a solid foundation for the Company’s wider activities today.

He joined the Company in 1966 as Development Officer, becoming Director of Research in 1973. In 1981, following a reorganisation, he became Director of Design & Technology until his retirement in 1988. Peter’s brief was ‘to drag the trade into the twentieth century’. In his twenty-two years at the Company he worked tirelessly and by the 1990s it was generally acknowledged that he had, to a considerable extent, succeeded. He had earned a formidable worldwide reputation for himself through his extensive knowledge of technical matters relating to precious metals and fabrication techniques.

Published by:The Worshipful Company of GoldsmithsGoldsmiths’ Hall , Foster Lane, London EC2V 6BN T: 020 7606 7010 F: 020 7606 1511E: [email protected] W: www.thegoldsmiths.co.uk

ISSN 1747-4256 (Print)ISSN 1747-4272 (CD-ROM)ISSN 1747-4264 (Online)

No part of this work may be reproduced, stored in a retrieval system or transmitted in any form or by any means including copying and recording, without written permission from the copyright owner, application for which should be addressed to the Goldsmiths’ Company. Opinions expressed in the Goldsmiths’ Company Technical Bulletin are not necessarily those of the Goldsmiths’ Company. Whilst every effort has been made to verify statements of fact by contributors, no responsibility is accepted for errors or omissions by them. Prospective users of the techniques, materials or equipment described should take specialist advice on official safety precautions and regulations which apply to them. Both may vary from country to country.

COPYRIGHT © 2007 The Worshipful Company of Goldsmiths

Image on front cover: The Cybaman replicator 6-axis CnC machine from Cyba manufacturing Technology ltd

E d i T O r i a l T E a mDr. christopher corti Technology Consultant to The Goldsmiths’ Company

Mark griMwaDe Metallurgical Consultant to The Goldsmiths’ Company

karin paynter Assistant to Director Technology & Training

peter taylor Director Technology & Training

ashley slater Associate Editor

Peter recognised the need for a more scientific approach to jewellery technology by the industry and involved Mark Grimwade (then at Sir John Cass) in a series of seminars on the metallurgy of jewellery, many of which were later published in Aurum and Gold Technology magazines. He instigated the production of the Goldsmiths’ Company Technical Reports and the TAC News. This knowledge was summarised in his excellent chapter, Jewellery Investment Casting, in the book Investment Casting, edited by PR Beeley & RF Smart, published in 1995 by the Institute of Materials, London. This included a history and review of investment casting and the casting machine technologies, as well as detailing current practice.

Peter was also responsible for the encouragement of excellence in design, promotional activities and exhibitions, including the ‘blockbuster’ exhibition The Jewellery of René Lalique, in which visitors were seen queuing round the Hall during the entire exhibition.

A man of considerable energy, talent and merit, he did much to enhance the standing of the Company, both at home and abroad. His contribution to advancing the technological quality of the UK jewellery industry is without question. He will be greatly missed.

The Technical Bulletin is produced and distributed by the Technology &

Training Department of The Goldsmiths’ Company. The purpose of this

publication is to address technical issues relevant to the UK Craft and

industry and increase technical knowledge and understanding among

those working within the industry. The Company welcomes feedback and

article submissions for inclusion in future editions.

Please contact the Technology & Training Department,

T: 020 7606 7010 or e: [email protected]

2 |THe GolDsmiTHs’ ComPAnY TeCHniCAl BUlleTin issUe 5 APril 2007

pETEr Edward gaiNSburyCEng Fimm

ObiTuary:

maTErialS maTTEr:

d i S C O l O u r a T i O N O F C a r a T g O l d J E w E l l E r y

maTErialS maTTEr: diSCOlOuraTiON OF CaraT gOld JEwEllEry1

THe GolDsmiTHs’ ComPAnY TeCHniCAl BUlleTin issUe 5 APril 2007 |3

Do you dread jewellery returned by the customer because it has discoloured? Are

they complaining of dark smudges on their clothes? mark Grimwade reports on the

tarnishing of carat gold jewellery and its causes - and how it may be reduced.

When returning an item, customers will often insist that gold should not discolour and that there must be something wrong

with the metal. They may complain that an item is causing black marks to appear on their skin and/or clothing. The latter case is often referred to as the gold smudge phenomenon. The discolouration is due to the fact that the carat gold alloy may tarnish in a manner similar to that of tarnishing of silver. Customers usually accept that silver will tarnish with time and must be cleaned periodically but they may not be aware that certain carat gold alloys can suffer the same fate. Blackening of skin and clothing may be caused either by mechanical wear and abrasion of the metal or by a combination of tarnishing followed by abrasion of the tarnish film.

TarnishingTarnishing has been defined as 'the visibly detectable discolouration caused by a thin adherent layer of a reaction product, such as an oxide or a sulphide, induced by a chemical reaction between the metal and its environment' (Ref. 1). It is, therefore, a type of corrosion. Pure gold has excellent corrosion resistance and it will not tarnish. However, the carat gold alloys usually contain both silver and copper as constituents and it is these elements that are responsible for tarnishing in some of the alloys. We shall return to the influence of carat gold alloy composition later in this article after discussing the mechanism of tarnishing and the factors affecting the rate of tarnishing.

It is generally recognised that the tarnish film on silver and its alloys and on the carat gold alloys consists mainly of silver sulphide (Ag2S), or a mixture of Ag2S and copper sulphide (Cu2S). The presence of other reaction products such as silver chloride, silver oxide, silver sulphate and other metal sulphides depending on the composition of both the alloy and the tarnishing environment has been reported.

The tarnishing reaction that is the most prevalent, although there are others, is

2Ag + H2s + ½o2 Ag2s + H2o

where H2S is hydrogen sulphide gas. It is known that tarnishing does not readily occur in the absence of oxygen (O2) and moisture.

The presence of sulphur and other tarnishing agents are necessary for the tarnishing reaction to proceed and these can be in the form of:• Atmospheric pollutants, such as hydrogen sulphide

and sulphur dioxide. This explains why tarnishing occurs more rapidly in industrial areas compared with countrified areas

• Human perspiration. An individual’s body chemistry is affected by diet, health and any medication that they may be taking

• Foods rich in sulphur, eg eggs, onions, spices, etc.• Cosmetics, perfumes, hairsprays, soaps, household

cleaners, etc.• Packaging materials. Care must be taken that items

of silverware and gold jewellery are packaged wrapped in anti-tarnish tissue paper or cellophane bags and placed in boxes that do not contain any sulphurous compounds, say in adhesives and rubber-based glues. Contact with rubber bands must be avoided. Anti-tarnish paper contains additives that tie up any bleaching constituents liable to react with the environment to produce sulphurous vapours.

The rate of tarnishing or discolouration is affected by:• The nature of the corrosive environment• The relative humidity in the atmosphere• The temperature. Chemical reactions occur at a

faster rate at increased temperatures. The heating effects of strong illumination on jewellery displayed in shop windows coupled with other factors may enhance tarnishing

• Metallurgical factors, eg alloy composition, processing history, surface quality, etc.

It is this last point that often sows the seeds of confusion in the minds of both the customer and retailer. It explains why a 9ct gold chain bracelet will discolour whilst the findings at the ends of the chain may not. In this case, the chain and the findings are made from different 9ct alloys. Similarly, it may be one piece of 9ct jewellery that is the culprit whereas other 9ct gold pieces in the customer’s collection do not tarnish. Items having a matt finish appear to tarnish more readily than those that are highly polished because of the increased surface area.

Tarnishing, when it occurs, is most common with the low carat golds, notably 9ct and 10ct although 14ct golds may be susceptible in hot climates. This is not surprising when it is considered that these alloys have higher base metal contents together with the silver content. It has often been stated that carat gold alloys will not tarnish provided the gold content of the alloy is greater than 50 atomic %, ie more than half of the atoms in the alloy are gold atoms. The statement comes from the work of Tammann reported in 1919 (Ref. 2) and is illustrated in Figure 1 for the ternary Au-Ag-Cu alloys expressed in terms of weight % composition. Since atomic % differs from weight %, due to the differences in the weights of the various metal atoms, the 50 at. % ranges from 15.6ct for pale yellow (greenish) Au-Ag alloys to 18ct red

1

Au-Cu alloys. It is a coincidence that the 75 wt. % Au-25 wt. % Cu composition is virtually 50 at. % of each. The diagram (Zone A) indicates that all alloys of 18ct and above should be immune from attack. Zones B and C indicate increasing susceptibility to attack. However, recent work shows that the Tammann statement is a generalisation and that under certain conditions the higher carat golds may tarnish. Indeed, Corti has reported the presence of tarnishing on 22ct gold jewellery samples obtained from India (Ref. 3).

To some extent, the above comments are academic because in the UK the problem is confined almost entirely to 9ct gold jewellery. Apart from variations in 9ct alloy composition, the processing history can affect the rate of tarnishing. For example, cold-worked or cast pieces tend to tarnish more rapidly than the same pieces given a homogenisation anneal of say 15 minutes at 650-700°C followed by a water quench. It is for this reason that 9ct alloys containing zinc tend to have a greater resistance to tarnishing. The presence of zinc extends the range of solid solubility in the low-carat alloys and hence the homogeneity of composition (Ref. 4). Unfortunately, the presence of zinc does increase the risk of stress corrosion cracking unless steps are taken to stress relieve 9ct jewellery items.

THe

Go

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Hs

'Co

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An

Y

Below:

9ct yellow gold

rings with tarnish

caused by

components

in the packaging

material


Zone C

20 40 60 80CuAg

80

60

40

20

Au

80

60

40

20

Zone A

Zone B

18 carat

14 carat

9 carat

Weight per cent copper

Wei

ght p

er c

ent s

ilver

15.6 carat

Weight per cent gold

There are accelerated tests to assess the rate of tarnishing on alloy samples, eg ISO 4358:1995, eg ISO 4358:1995, egbut these are not suitable for retailers or most studio/workshops. In addition, the results need to be interpreted with caution because it is virtually impossible to take into consideration all of the various factors that influence tarnishing.

mechanical wear and abrasionMechanical wear is particularly evident on chain links, pendants and rings where there are constant rubbing movements within the piece or against other pieces. This can produce debris in the form of very fine metal dust that collects with grease from the skin in crevices or which may eventually rub off as black marks on skin and clothing. Even gold dust in sufficiently finely divided form will appear to be black. This, of course, can show up for any caratage of jewellery. Work done for the Goldsmiths’ Company at the end of the 1970s showed that the generally held belief that 9ct alloys are more wear resistant than 18ct alloys is unfounded (Ref. 5). Another result of the same investigation was that although wear rates on 9ct and 18ct gold wedding bands were virtually the same for any particular individual, there were great variations in wear rates between individuals. The reasons for the variations were not explained but it suggests that differences in an individual’s lifestyle, body chemistry, etc., do play a part. Tarnish films that are so thin that they are not immediately obvious to the wearer will also rub off.

Therefore, in this case, the blackening is due to a combination of both chemical attack and mechanical wear and abrasion. The type of clothing worn has been shown to have an effect. Modern synthetic fibres are harder and more abrasive than softer wool or cotton and are more likely to show blackening on clothes.

What should we tell the customer?In my experience, the vast amount of low-carat jewellery items purchased by the public do not appear to present a problem. Nevertheless, when it does occur the jeweller/retailer needs to offer conciliatory advice to the customer. It should be explained that some pieces of 9ct jewellery may tarnish either due to the alloy composition or to other factors such as lifestyle, environment, etc. It is not possible always to use an alloy composition with a low tarnishing rate because the composition may be determined for other reasons, eg colour, ease of processing, etc. Jewellery must be treated with care in order to minimise the risk of tarnishing.• Try and avoid wearing jewellery in the presence of

domestic cleaning fluids

maTErialS maTTEr: diSCOlOuraTiON OF CaraT gOld JEwEllEry

• Apply cosmetics and perfumes before putting jewellery on

• If worn in chlorinated swimming pools, rinse off in clean water as soon as possible

• Accept the fact that it is highly unlikely that there is anything wrong with either the metal or processing and that it is necessary to periodically clean items to remove tarnish films and prevent their build-up just as the customer would do for silverware.

With regard to this last point, it is a good idea for the jeweller/retailer to quickly show the customer how to clean the item, say with an anti-tarnish cloth followed by washing with a mild detergent and then rinsing thoroughly and drying with a soft cloth. This can be done on a no-charge basis at least on the first occasion and helps to satisfy the customer.

Finally, in extreme cases, it may be possible to hard-plate the item with a high-carat gold but it must be recognised that this may wear off with time.

MarkMarkM griMwaMwaM DwaDwa e

Mark Grimwade has been a consultant to the Worshipful Company of Goldsmiths over many years and authored the books, 'An Introduction to the Precious Metals', published in 1985, and the ‘Handbook on Soldering’ in 2002 for World Gold Council. He has written extensively on jewellery materials, including the ‘Basic Metallurgy for Goldsmiths’ series in Aurum magazine and in Gold Technology. He has presented many times at the Santa Fe Symposium and has lectured extensively on jewellery technology around the world as a consultant to World Gold Council. He plans to write an updated version of his book shortly.

references1. JJ Tuccillo and JP Nielson, J Prosth. Dent., Vol. 25, p629, 1971

2. G Tammann, Z Anorg. Allg. Chem., Vol. 107, pp1-240, 1919

3. C Corti, Proc. Santa Fe Symp. on Jewellery Manufacturing Technology, p29, 2000

4. WS Rapson and T Groenewald, Gold Usage,pp80-85, Academic Press, 1978

5. B Taylor, TAC Project Reports No. 43/1-3, The Goldsmiths’ Company, 1978-80

Figure 1: Tarnishing and corrosion behaviour for Au-Ag-Cu alloys


maTErialS maTTEr:

T H E H a r d N E S S O F J E w E l l E r y a l l O y S w H y i S i T i m p O r T a N T ?

may crack and even fracture. We know we need to anneal (ie heat up) the metal at some point to restore some measure of malleability and allow further working in safety. We call the annealed state the ‘soft condition’. This observation tells us that for that particular jewellery alloy, its hardness value can vary from ‘hard’ to ‘soft’. We all know that different metals and alloys have differing hardness values - nickel white golds are harder than palladium white golds at the same caratage, for example. In this context, it is sometimes asked whether 950 platinum is harder than 18ct gold. The answer depends on which alloys are being compared. 950 platinum and 18ct gold alloys can vary in their annealed hardness, depending on the particular alloy compositions being considered.

Hardness is one of the mechanical properties of metals and materials (including gem stones) and its value is indicative of other properties as well as the metallurgical condition of a particular alloy composition. Indeed, the property of hardness largely determines a material’s resistance to scratching, wear, machineability and the ability to cut other materials. It is an inexpensive, quick and non-destructive means of evaluating mechanical properties, a relatively easy property parameter to measure and consequently frequently used by researchers and manufacturers alike, the latter often in a quality control context.

What is Hardness and How Do We measure it?There are many methods of hardness measurement; many involve pressing a hard indenter into the material under controlled conditions of time and force and measuring the size of the indentation produced. Thus, hardness can be defined as the resistance of a material to plastic deformation. There are a number of hardness scales of measurement (as with temperature, where we use Celsius, Fahrenheit and other scales), the most common being Vickers,

It is often asked what importance hardness values play in jewellery. The question is often posed in terms of the fabrication of jewellery, but rarely in

terms of the subsequent service performance when worn by the customer. However, in discussing what role hardness plays in jewellery, we should also link it to how the jewellery behaves in service, if we want our customers to be happy with it.

All jewellers appreciate that as we work (ie deform) a jewellery alloy, it gets more difficult to work further (it gets harder) and if we overwork the metal, it

Hardness is one of a number of mechanical properties of jewellery alloys that can be

easily measured. its value is of importance in fabricating jewellery and in the subsequent

performance of that jewellery when worn by the customer. Christopher Corti explains

hardness and why its value needs to be considered when making jewellery.

1

Below:

Hardness testing

machine

KA

rin

PAY

nTe

r


maTErialS maTTEr:

T H E H a r d N E S S O F J E w E l l E r y a l l O y S w H y i S i T i m p O r T a N T ?

maTErialS maTTEr: THE HardNESS OF JEwEllEry allOyS

Brinell and Rockwell. Like temperature, each method results in a different numerical value for the same metal sample and so we distinguish the measurement values by the symbols HV, HB and HR respectively. Of other types of hardness test, the Scleroscope test measures the rebound of a dropped hammer and the Mohs test for minerals is a comparative scratch test. For metals and alloys, the Vickers test, involving a diamond pyramid indenter is, perhaps, the most commonly used.

The Value of HardnessHardness values can be correlated to a material’s other properties; for example to its tensile strength, or strictly speaking, yield strength. In general, the harder a material is, the stronger it is and the more resistant it is to wear and to scratching, properties that are relevant to jewellery. It also affects the durability of jewellery, such as security of claw settings, distortion, and dent and damage resistance.

As an indicator of metallurgical condition, it can show if an alloy is in the annealed, soft condition or cold-worked (deformed) or age-hardened conditions. The metallurgical condition of a particular alloy will determine its ability to be deformed (malleability), its ductility, its strength, its stiffness and other properties relevant to its fabricability and its service performance. For example, polishing of jewellery alloys is easier to achieve on a harder material or a material in a hard metallurgical condition.

If a jewellery alloy is too soft, it will not be durable in service. A soft post on an earring will bend, a soft spring alloy will not be very efficient and a soft hollow bangle will easily dent, all leading to customer dissatisfaction. In a paper presented at the 2005 Santa Fe Symposium, Valerio Faccenda discussed many cases of customer complaints received by the Pomellato Company in Italy. He cited one case of excessive wear on an 18ct gold chain-style bracelet. The problem was addressed by heat-treating the bracelet to make it harder and, thus, more wear resistant.

Hardening of metalsAll pure metals tend to be relatively soft and often not ideal for practical applications that involve stresses and strains, tending to wear heavily or deform/distort during service. For most practical applications, harder, stronger materials are desirable. Hardening

can be achieved by cold working (deforming) or by alloying the metal or a combination of both. Cold working inevitably involves a loss of some ductility and hence results in a greater potential to fracture during service. A disadvantage is that hardening by cold working is lost on heating (annealing, soldering, welding operations at elevated temperatures, etc.) and is, therefore, not necessarily a durable condition.

Alloying gives more scope to tailor properties. Thus, we alloy copper with zinc or tin to give brass or bronze, iron with carbon, chromium and other metals to give steels, aluminium with copper, magnesium, etc. to give aluminium alloys and so on. Of course, we also alloy to improve other chemical or physical properties such as corrosion and tarnish resistance or thermal expansion. Stainless steels are an example of the former.

Jewellery Alloys Silver, gold and platinum are all soft, very ductile metals and are not very practical for jewellery application. They all have hardness values in the HV20-30 range in the annealed condition which is a very low value on the scale of hardness of metals and alloys. Silver, in its fully work-hardened condition, can attain a hardness of around HV100 but has virtually no residual ductility, making it unsuitable for fabrication, ie it cannot be further shaped and would be liable to fracture during service under imposed stresses and knocks.

Above:

A Vickers hardness

impression


100

200

900

800

700

500

400

300

10 20 30 40 50

600

0

0 60

% Cold Work

Ha

rdn

ess

, HB

: TS

(M

N/s

q.m

) TS 18ctHB 18ctTS 24ctHB 24ct

Gold is alloyed, typically, with silver and copper to give the carat golds, platinum with a number of alloying metals to give a range of 950 or other fineness alloys, silver with copper to give Britannia silver, sterling silver and other lower finenesses, all with higher hardnesses and tensile strengths than the pure metals. Consequently, their wear and scratch resistance is better, their higher strength allowing better dent and damage resistance and, where relevant, lighter weight for acceptable performance. However, alloying does tend to reduce ductility and malleability (but not as severely as cold working). Pure gold can be cold-worked to extremely thin gold leaf, but carat golds cannot.

The metallurgical condition of jewellery alloys also impacts on their fabricability and service performance. Cold working (eg deformation by rolling, drawing, hammering bending, etc) increases hardness and strength but at the expense of ductility and overworking will result in cracking and eventual fracture. So, it is often necessary to anneal cold-worked (ie deformed) metals at stages in their fabrication to restore ductility and allow further

1

working towards the final shape. This involves heating the metal above a critical temperature for a period of time, with a gas torch or in a furnace. This causes a process of recrystallisation, in which the deformed metal crystals (grains as metallurgists call them) reform (ie recrystallise) into new undeformed grains, thus softening the metal back to its original condition. In general, the as-cast hardness of a metal or alloy will be similar to its annealed hardness but this may not be so in all cases.

For some alloys, it is possible to further harden alloys by a process called heat treatment. Known as age-hardening or precipitation hardening, it involves precipitating out fine dispersions of second phases within the alloy microstructure by a two stage process of solution annealing at high temperatures, rapidly cooling and then ageing at a low temperature for a fixed period of time. For 18ct red golds it is possible to double the hardness by this technique, based on the order-disorder transformation, albeit at the expense of some ductility. Engineering alloys such as those of aluminium, alloy steels and nickel-based ‘superalloys’ for aerospace and automotive application also utilise precipitation hardening to achieve high mechanical performance.

Hardness Values of Typical Jewellery AlloysTypical hardness values of the pure precious metals and common jewellery alloys in several metallurgical conditions are shown in the table. The effect of both alloying and cold work on hardness is evident. In terms of alloying, for carat gold alloys, copper is clearly more effective in hardening than silver. For platinum alloys, there is a range of hardness values for different alloying metals at the 5% level (annealed condition) ranging from HV60 to HV180. Cold working also has a substantial effect in hardening: for carat golds, a hardness increase of around HV60-70 is obtained (over annealed hardness), and even higher increases can be obtained in 950 platinum alloys. For sterling silver, an increase of about HV50 is seen, similar to that found with the carat golds. An important point to note is that it is possible to age- harden sterling silver but where soldering is involved in jewellery manufacture, any hardness benefit is lost due to the annealing effect of heating the metal to the soldering temperature.

We can draw some general observations from this table. Firstly, the annealed hardness of 22ct gold at HV52-70 produces relatively soft jewellery, which does not wear well. It is too soft to make catches such as lobster claws. At 21ct and 18ct, hardnesses of HV100-120 and HV150-170 respectively, are considered satisfactory for jewellery application. We also note that 950 platinum -5% iridium at HV80

100

200

500

400

300

20 40 60 80 100

600

0

0

Copper Atoms added to gold (at %)

Har

dn

ess,

HB

:TS

(MN

/sq

.m)

HB

TS

Figure 1.

Effect of cold work on

hardness and tensile

strength of fine gold

and 18ct gold

(TS = tensile strength,

HB = Brinell hardness)

Figure 2.

Effect of alloying

on hardness of

gold-copper alloys


maTErialS maTTEr: THE HardNESS OF JEwEllEry allOyS

Table:

Hardness of pure precious

metals and common

jewellery alloys

Note:

Data taken from

manufacturer’s information

or independent sources

for generic alloys. Where

single values are given,

these are typical; real

values will lie within a

narrow range

and platinum -5% gold and platinum -5% palladium at HV90 and HV60 respectively, are considered too soft for jewellery unless they are hardened by cold working. Mark Grimwade (Goldsmiths' Technical Bulletin Issue 1, 2005) notes that cast platinum - 5% gold rings are seen to suffer badly from consumer damage (wear, nicks, etc.) due to their low hardness of about HV90. (We should note that net shape as-cast materials - investment cast rings, for example - will be in the soft annealed condition and can only be hardened by heat treatment, if that is an option for a particular alloy, as cold working would destroy the net shape.)

Thus, we can conclude from practical experience that for reasonable wear, scratch resistance and durability during service, a hardness of at least HV100 is desirable for jewellery. This conclusion is supported by a paper presented at the 2006 International Santa Fe Symposium on Jewellery Manufacturing Technology (see report in this issue), where Teresa Freye of the Techform casting company, spoke about casting of the new 950 palladium alloys. One criterion for selection of alloys for detailed casting trials was a requirement for an as-cast hardness of HV110 minimum.

This minimum hardness value can be obtained in sterling silver in the work-hardened condition but it has little residual ductility in this condition. So use of sterling silver in jewellery can be problematic from this standpoint, particularly where annealing and or soldering operations are involved in its manufacture, as it will become softer, although more ductile, and age-hardening is not feasible where soldering operations are involved. In this context, it is worth remarking that one of the newer tarnish-resistant silvers developed in the UK, known as Argentium, can be subsequently age-hardened (after soldering) without the need for a first-stage high temperature anneal and still achieve a hardness of HV110. If the full two-stage process is applied, this hardness increases up to HV125. Perhaps this is another good reason to consider such an alloy for silver jewellery application.

Higher hardnesses in the HV200-300+ range, as we can obtain in 18ct and lower carat golds, for example, are even better in the context of service performance and we should note that some platinum alloys are also age-hardenable with values of around HV350 achievable.

ConclusionsThe significance of hardness as a measurement of the mechanical properties of metals and alloys has been discussed in the context of the fabrication of jewellery and in its subsequent performance in service. There is a universal and general correlation

metal/Alloy Alloying metals, % Hardness (Vickers) Condition

Gold - 20-30 Annealed

55 c.w.

silver - 22 Annealed

100 c.w.

Platinum - 30 Annealed

22ct gold 5.5 Ag, 2.8 Cu 52 Annealed

138 c.w.

3.2 Ag, 5.1 Cu 70 Annealed

142 c.w.

21ct gold 4.5 Ag, 8.0 Cu 100 Annealed

190 c.w.


197 c.w.

18ct gold 12.5 Ag, 12.5 Cu yellow 150 Annealed

212 c.w.

230 age-hardened


red 227 c.w.

325 age-hardened

Britannia silver 4.2 Cu 45 Annealed

95.8%

sterling silver 7.5 Cu 66-76 Annealed

92.5% 116-130 c.w.

950 platinum 5 Pd 60 Annealed

5 ir 80 Annealed

140 c.w.

5 Au 90 Annealed

300 age-hardened

5 ru 120-130 Annealed

220-230 c.w.

5 Cu 120 Annealed

5 Co 135 Annealed

270 c.w.

Ga + in + Cu 175-185 Annealed

340-360 c.w.

340-360 age-hardened

900 platinum 10 Pd 80 Annealed

10 ir 110 Annealed

between certain properties and an alloy’s hardness value. The harder the metal, the easier it is to polish and the more wear and scratch resistant it will be.

The hardness value for a metal or alloy also is a measure of its metallurgical condition, which affects its fabricability in jewellery manufacture. Thus, for each metal or alloy, its hardness can be increased by work-hardening and, for some alloys only, by age- hardening or a combination of both. The soft annealed or as-cast condition will confer the best ductility but the poorest resistance to wear and scratching.

The hardness values of the pure precious metals and common jewellery alloys have been discussed. For reasonable wear resistance and service performance, a hardness of at least HV100 is desirable, whether gold, silver or platinum jewellery.

christopher w. corti

Key to Symbols: Ag - silver, Cu - copper, Pd - palladium, Ir - iridium, Ru - ruthenium, Au - gold, Ga - gallium, In - indium, Sn - tin, Zn - zinc, c.w. - cold worked (values typically after 50-80% reduction)


2

Brown and Newirth, aka B&n rings ltd, is over 30 years old and is part of the Abbeycrest Group. I met with Gary Williams, Sales

Director, and Tamsyn Wills who is Design, Research and Development Manager. She is responsible for technology in the company, as quickly became evident, and the link between innovative design and enabling technology was foremost in our discussions.

Based in Hatfield, in a modern, purpose-built three- storey building, with 93 employees, the business has grown and, after some seven years, is bulging at the seams in terms of production floor space. Gary made clear that the benefits of investing in technology for B&N were two-fold: firstly, to produce quality product faster and better and, secondly, to grow the business. Tamsyn also emphasised that part of her challenge is to stretch the capability of the new technology to achieve things not previously considered possible. Flexibility is an important part of the business and this is reflected in its production capability.

B&N makes quality rings, mainly for the independent retailer but also some mass retailers. It originally manufactured plain and diamond-cut wedding bands and has since grown its range to include engagement rings and complementary jewellery. Today, B&N’s main focus continues to be the bridal market, producing mainly 18ct gold and 950 platinum products, but it has been extending into new areas such as high quality diamond products. An area of current interest is the new 950 palladium market into which it is launching. It operates in the middle- to high-end sector of the market.

As has been mentioned previously, investing in technology includes people as well as machines, IT systems and software. It was no surprise, therefore, to learn that Tamsyn was part of B&N’s technology investment five years ago. With a BA in 3D Design and a Masters in Manufacturing Engineering (Herts. University), Tamsyn originally joined B&N as a Teaching Company Associate (TCA). In association with the Technology and Innovation Centre, University of Central England, Birmingham, this was a two-year project to introduce 3D CAD technology in both design and production and integrate it into B&N. At the end of the project, she took on her new, current role within B&N. Her enthusiasm for, and knowledge of, technology came through as we toured the factory.

Walking around the factory, it was apparent that a number of new technologies have been introduced over the years, although the traditional technology of roll forming ‘washers’ to make bands and subsequently manually machining these on a lathe and/or diamond cutting still forms part of the production approach. Now CNC diamond faceting/milling machines, for example, have added to these facilities and improved production in terms of quality, speed, accuracy and complexity of design. In addition, these are complemented by a laser welder, in constant use for a variety of applications such as repair of defects, and a ‘sintering’ machine for diffusion bonding of bimetallic rings, bought last year. The finishing department also includes modern barrel, drag and turbo disc polishers and plating facilities (for rhodium plating white gold), although traditional hand polishing is still important for final polishing. Complementing these were annealing

iNvESTiNg iN TECHNOlOgy:

b & N r i N g S l i m i T E d in the last in our current series on ‘investing in Technology’, Christopher Corti looks

at a manufacturer of rings, Brown and newirth, and examines how continuous

investment in technology helps to grow the business and, importantly, enables the

development of new designs not achievable using traditional technology.

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Below:

An example of rings

produced using

the laser sintering

machine

Bottom:

Fire & Ice coloured

diamond collection,

cut using B&N’s

precision laser

cutting machine


furnaces - both belt and muffle types. Fronting up these facilities are both 2D and 3D CAD systems in the design department, which are also essential for the newer technologies I will mention shortly. CAD plays a significant role in design and in enabling computer-aided manufacture (CAM) as a central production technology. A number of software applications are in use, including DeskArtes, Rhino, Type3 and HyperMill, the latter feeding B&N’s Cybamatic 6-axis simultaneous machining centre. Rapid prototyping is used for new designs but is currently sub-contracted. A problem, Tamsyn remarked, has been burnout of the resin models for casting, which leaves ash residues in the mould cavity, although the RP producers are making progress here.

As well as a number of conventional production departments, there is a technology department, for which Tamsyn has responsibility, where new technologies are developed and integrated into production. This department produces products that other departments cannot and houses the computer-controlled laser cutting/engraving and the Cybamatic machines. The laser engraving machine is run by a 2D CAD/CAM programme and enables quite amazing designs. It cuts complex patterns and also square and marquise settings accurately in minutes. It can be used for offering an individual service for engraving outside surfaces of rings; engraving inside surfaces is also possible but not offered as a service currently. The Cybamatic machine is run by a 3D programme and is still being ‘stretched’ in terms of its capabilities. I was impressed by the complexity and quality of the rings it is producing. As Tamsyn remarked, these two machines “are doing things that others cannot or aren’t doing!”

One reason for their introduction was to have more control over production of items formerly sourced from sub-contactors. Lead times for such contractors of two to three weeks were undesirable, resulting in the holding of stocks of castings, and so in-house production was deemed necessary. An in-house investment casting facility could not be justified as cast items form only a small part of the product range and it would not be used regularly.

As one might expect, the setting and mounting departments are still traditional, with skilled operators working at benches. The latter department produces B&N’s hand-made products, Celtic rings for example, and the use of setting machines in the former for setting small stones was a major advantage in reducing production time. Recruitment of skilled workers is a problem at B&N, as elsewhere in our industry, and a mixture of experienced and new employees are recruited with in-house training for the latter. Upgrading people skills is an important part of technology

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investment. "Investment in knowledge and people is needed to grow technologies", explained Tamsyn. “You cannot just employ people with the skills needed, as they do not exist.” Passing on her expertise to her team is an important part of growing the technologies in her department.

Operating a factory efficiently is an important part of B&N’s business if it is to meet customer demands. As one might anticipate, an integrated computer system enables orders to be programmed into the production schedule and tracked through production. The original ‘open plan’ factory layout has also been modified into discrete departments, which has led to greater efficiency. The factory is neat, tidy and clean and well organised, despite space being at a premium.

I was impressed with what I saw and the people I met. B&N Rings is good example of a successful, growing UK business that has recognised the importance of investing in technology - in producing innovative designs, in improving production quality and efficiency and, thereby, in achieving its business objectives. I have no doubt that B&N Rings is committed to investing in technology and will continue to do so.


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Top:

Selective laser

sintering at B&N

Above Left:

State of the art

sintering technology

fuses multicolour

metal permanently as

demonstrated in this

image of B&N’s new

palladium and 18ct

gold rings

Above Right:

Personalised phrases

can be lasered into any

ring using B&N’s state of

the art equipment.

Handwriting can be

copied exactly for an

extra personal touch

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3

On the materials front, palladium jewellery caught the eye, with several alloy suppliers claiming to have palladium alloys on the

market. The German alloy supplier, Wieland GmbH, was marketing a new range of palladium alloys at 950 and 500 finenesses. In addition, a well- known German jewellery manufacturer had a range of 18ct/750 fineness palladium jewellery on display. Turning to electroforming, the Swiss electroplating company, Pino Aliprandini, promoted cadmium-free electroforming baths for 18ct pink and yellow gold and also electroforming baths for 21ct and 22ct gold, previously thought not possible on a production basis. It also featured electroforming technology with gem stones in place, which will widen electroforming’s appeal to many jewellers.

indutherm GmbH of Germany had two new developments on display: firstly, an innovation in investment casting machine technology - casting with vibration. Its VC600V machine incorporates a flask vibration facility claimed to reduce porosity and yield a finer cast grain size. For small casters, there were two new benchtop mini investment castings machines on display. The most eye-catching was the Indutherm MC15 model which has a casting capacity of 240g of 18ct gold, a maximum temperature capability of 1950°C (enabling platinum and steel to be cast) and a power requirement of only 3.5kW. It is a very neat design with many good features and retails at E6,200, with a vacuum pump as an extra, if needed. This is ideal for the small studio caster/goldsmith and will no doubt prove to be popular.

On the CAM side, there continue to be new models of multi-axis machining centres. Carl Benziger GmbH had a new 5@light compact computer-driven milling centre, a 5-axis machine which meets customer requirements for a compact cost and space-saving solution to milling, diamond cutting and stone setting. An American manufacturer, Cms, displayed its GT Express range of compact desk top CNC turning centres, with a 4000rpm, 27mm spindle as standard. This technology features a solid polymer base that decreases vibration, gives better stability and increases tool life.

Jewelryscanner exhibited its 3D-Scan, a compact machine with 5-axis scanning technology that converts models and unique jewellery items into CAD/CAM data quickly and cost-effectively with high precision. This retails at around E15,000 and is marketed in Europe by laserdenta AG of Switzerland.

Robotics is a new area of production technology slowly entering the industry. Last year, Buko of Belgium demonstrated robot-based polishing operations on jewellery. This year it was a robot carrying out automatic wax injection for investment casting. This ensures consistent waxes and eliminates much labour. It grabbed a great deal of attention at Basel and demonstrated what is possible with robots in terms of reducing costs, improving quality and eliminating hazardous operations involving manual labour.

Lastly, a new desktop rapid prototyping machine, the Perfactory® Desktop, from envisiontec, is claimed to be a cost and technology leader and is a simplified version of its well-known RP machines. It retails at just under £20,000 (or can be leased). The build envelope measures 40 x 30 x 100mm and operating costs are reasonable. There are a range of resins suited for various applications including direct investment casting.


NEw TECHNOlOgy FOCuS:

l a T E S T p r O d u C T N E w S

Advances in technology and materials for our industry continue apace. each year, new

developments bring benefits to jewellery manufacture, many of which are traditional

technologies, not just the new ones such as CAD or rapid Prototyping. Here are a few

recent innovations that have caught Christopher Corti’s eye.

The new VC600V Indutherm

vacuum casting machine with

vibration casting technology

Perfactory® XGA

Desktop System. Based

on the principle of

photopolymerisation this

system creates three-

dimensional resin models

through a patented Direct

Light Projection System

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Indutherm MC15

Mini Investment

Casting Machine

This microscopic image from

Indutherm above shows the

grain structure of an 18ct gold

alloy without vibration, the one

below shows the result with

vibration casting


Do you have a manufacturing problem? For example, are you having trouble finding

a suitable alloy for a particular application, problems preventing porosity in your

castings or difficulty adjusting the colour of your solder to match an item? This is your

opportunity to ask the experts for advice.

email your questions to: [email protected] quoting ‘Technical surgery’

Q. i would like to get a very white finish on silver jewellery i have seen used in Germany. i understand it is achieved by heating and dunking into acid.

a.The very white colour on sterling silver is achieved by creating a very thin layer of pure silver on the surface. This can be carried out in two ways: 1. Heat the silver to produce a black copper oxide layer on

the surface and then acid pickle off the copper oxide. Oxidation of the copper will leave the silver surface layer deficient in copper, ie enriched in silver and hence whiter. This can be repeated several times to build up the silver-rich surface. There may well be some sub-surface firestain formed too. A problem with this approach is that subsequent polishing will slowly remove the white silver layer and reveal the original sterling colour or any firestain below. 2. Electroplate the surface with pure silver. Rhodium or palladium, will not be quite as reflective but will be more tarnish resistant. Note: The pure silver surface layer will not improve tarnish resistance significantly.

Q.i would be grateful for some information on acid etching platinum. i know it can be done with Aqua regia solution but this is extremely strong and i would appreciate some advice.

a.As with gold, there are few acids that will dissolve platinum. Aqua Regia (a mixture of nitric and hydrochloric acids in 1:3 ratio) is one of the few. You will probably need to use it for etching in a diluted form. As you say, it is strong and potentially hazardous. So it must be handled with care. Store in glass containers with screw caps. Keep away from heat, other chemicals and store in a secure cupboard. Take all health and safety precautions in handling acids - wear protective clothing and goggles, work preferably in a fume cupboard. If

you need to dilute the acid mixture, add acid to water, not the other way round. If acid splashes on your skin or clothes, wash immediately in copious amounts of water, eg a shower or running cold tap. Do not discard waste acid directly down the sink. It should be neutralised first.

Q. i am a silversmith, working in the antiques trade. A big problem i face is silver that has been previously repaired with lead-containing solder, which i want to remove. i have tried glacial acetic acid mixed with hydrogen peroxide, which dissolves the tin in the solder but also eats away the silver. is there another chemical that will eat away the lead but not touch the silver?

a.This question had us thinking, but we found the answer in a book by Staton Abbey, The Goldsmiths and Silversmiths Handbook 2nd Ed., published by Technical Press 1968. He says that the common method for dealing with this problem is to remove as much of the soft solder as possible by scraping it away. On no account must the article be heated or annealed as this will cause greater diffusion of the lead into the piece. After scraping, place the article in ‘fairly strong’ hydrochloric acid for some time. This should remove the remaining lead solder. Remember to treat all acids with care, as discussed in the previous answer.An alternative method that he gives is to prepare a solution of 50g ferrous sulphate, 25g potassium nitrate and 125g (ml) water. Boil the preparation for some time and allow the liquid to cool. Some crystallisation will occur. Decant the liquid and re-boil it. On cooling the second time, further crystals will form. Finally, the crystallised salt should be dissolved in hydrochloric acid in the proportion of 10g of salt to 80g acid. Add 40g (ml) of boiling water to 10g of this preparation, and keep at boiling point. Staton Abbey concludes that ‘even the most obstinate soft solder will be cleanly and entirely removed if the work is immersed in the boiling solution for a short time’.

TECHNiCal SurgEry:

a S k T H E E x p E r T S

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The annual international Santa Fe Symposium is the foremost source of the latest research advances and technical information on

jewellery materials and manufacturing technology. The cognoscenti in our industry know that much of the industry’s current state of knowledge on jewellery alloys and manufacturing practice has been featured first at this symposium over the years.

PalladiumThis year’s symposium was notable for featuring the new jewellery metal - palladium. This has been a very hot topic in the US, Chinese and European jewellery industries over the year, with most US alloy suppliers launching new 950 palladium alloys and the retail industry showing serious interest. However, a full technical appraisal of palladium has been awaited and the three presentations ensured a technical understanding of the metal was placed on a sound footing. Palladium as an alternative white jewellery metal is of interest because its low price and low density (compared to gold and platinum), coupled with its good white colour and tarnish resistance, makes it a very cost-effective alternative to both 18ct white gold and 950 platinum, with retailers able to obtain more attractive margins too.

The first presentation, The Working Properties for Jewellery Fabrication using New Hard 950 Palladium Alloys was by Prof. Paolo Baittaini of 8853 spa in Italy, who described progress to develop two prototype 950 palladium alloys for wrought application. The initial work was based on palladium-copper and palladium-gallium alloys with indium and other alloying additions. The annealed hardness of the gallium alloy, HV170, was much higher than the copper alloy at HV70 and its melting range substantially lower. Cast ingots were subjected to cold rolling and annealing cycles down to thin sheet. This sheet was further subjected to a number of mechanical processing operations and the evolution of the metallurgical structure and properties followed. This included roll forming with continuous TIG welding to form seamed tube that was further drawn down to tube of 8.5mm diameter (easily accomplished but good lubrication was important) and the blanking of washers, drawing and ring rolling to form ring blanks. In addition, square bars were rolled and then drawn to wire of 0.7mm diameter using diamond nibs in the dies. Good lubrication was also important here. Tensile tests were performed on the wires. Typically, cold-worked hardnesses of HV220 or higher were achieved before annealing to a hardness of HV180 for the gallium alloy and HV170, annealed down to HV72 for the copper alloy. Good fine-grained, equiaxed microstructures were obtained.

Laser welding and brazing studies were carried out on the Pd-Ga alloy; the need to identify the correct process parameters was found necessary for successful laser welding and the use of an 18ct nickel white gold filler allowed successful brazing with an oxy-propane torch. This work showed that the palladium-gallium alloy was the most promising of the two examined. The mechanical strength of the drawn and annealed wires was better than some platinum alloys and indicated its suitability for chain manufacture.

An initial study, Palladium Casting: An Overview of Essential Considerations, into the investment/lost wax casting of 950 palladium alloys was reported by Teresa Frye of TechForm Advanced Casting Technology in the USA. This company specialises in shell-mould casting of platinum jewellery and other high-tech metals for the aerospace and dental/

Christopher Corti reports from the 20th santa Fe symposium on Jewellery

manufacturing Technology.

rEpOrT:

i N T E r N a T i O N a l S a N T a F E S y m p O S i u m 2 0 0 6

5

Below:

Delegates at

the Santa Fe

Symposium

listening to a talk

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medical industries. The purpose was to obtain a better understanding of the casting characteristics of the new 950 palladium alloys appearing on the market in comparison to the casting of platinum jewellery alloys. Frye covered several aspects: in wax sprueing she noted that use of more auxiliary feed sprues were required for palladium thin sections to facilitate filling of the mould cavity. Like platinum, investing the mould required use of phosphate-bonded investments due to their high melting ranges (1400-1500°C). Techform uses ceramic face coats prior to investing the wax tree, but considered this was not necessary. Any investment suitable for platinum should work well for palladium.

Frye found that the actual casting of palladium posed the biggest technical challenge. This was due mainly to the risk of oxidation, unlike platinum, and so use of protective atmospheres was essential. She also noted that overheating of the molten metal increased the chance of oxygen absorption with consequent defect formation (gas porosity) during solidification. Devesting of the cast metal from the mould was found to be relatively straightforward, with use of boiling diluted sodium hydroxide solution followed by water blasting.

The study reported by Frye was conducted on palladium alloys selected on the basis of certain criteria, including a minimum hardness of HV110,

rEpOrT: iNTErNaTiONal SaNTa FE SympOSium 2006

rEpOrT:

i N T E r N a T i O N a l S a N T a F E S y m p O S i u m 2 0 0 6

ductility, recyclability, melt cleanliness and fluidity. This resulted in six commercial alloys being evaluated, with casting temperature of 1600°C, flask temperature of 950°C and vacuum followed by argon backfill atmosphere. Three of the test alloys resulted in brittle, defective castings whilst the other three were ductile and crack-free. When the alloys were cast without vacuum, ie only argon cover, five of the alloys cast well; suggesting vacuum was detrimental to some alloys. SEM analysis of a ductile fracture face showed the presence of low melting gallium-rich particles on the grain boundaries.

Based on this initial evaluation, Frye concluded that the best casting alloy was Hoover & strong’s TruPd 950 fineness alloy. This was subjected to form-filling casting tests using standard grid patterns and the highest metal pour temperature of 1760°C gave the best form-fill. Similar good fills were obtained in comparative trials on 950 platinum-ruthenium alloy, cast at 1980°C. Examination of cast rings in TruPd under the same conditions showed a lack of porosity. Frye concluded that there is still much work to be done on casting of palladium alloys, which present unique challenges compared to other precious metals. Recyclability is of particular concern.

Barrie-John Williams of Johnson matthey, New York, gave the third presentation on palladium jewellery alloys, Palladium - Light, Bright and Precious - A Jö

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Left:

Cross-section of crack

surface of sterling

silver main sprue,

opened after blasting

and pickling, showing

interdendritic porosity

and internal oxidation.

From Jörg Fischer-

Bühner’s paper

on Improvements

of Sterling Silver

Investment Casting

Below:

Cross-section of

sterling silver showing

even distribution

of gas porosity.

From Jörg Fischer-

Bühner’s paper

on Improvements

of Sterling Silver

Investment Casting

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modelling of the investment casting of silver which was excellent. This year, Jörg Fischer-Bühner reported on an EU-funded project on the investment casting of silver. The collaborative partners included two UK casting companies and the Jewellery industry innovation Centre at UCE. The aim was to understand the causes of casting defects and to develop practical approaches to reduce their incidence.

Yet again, this work was top class and yielded both a silver defects handbook and some easy-to-implement recommendations on investment casting of sterling silver that lead to considerably reduced defect levels in the castings. These are based on the finding that many porosity and inclusion defects are associated with oxygen uptake. The steps recommended involve degassing the silver, taking longer to evacuate the flask before casting and increasing the time before removing the flask from the chamber.

Another paper by Tony Eccles of Apecs investment Casting Pty in Melbourne, Australia, focused on the effects of trace elements on casting of bright silver alloys containing germanium or silicon, developed by Tony. Defect levels in casting and nodules on soldering were discovered to be related to trace impurities in the alloys, particularly selenium, tellurium and bismuth. These new findings impact many silver casters. The importance of keeping these trace impurities to very low levels was emphasised.

PlatinumPlatinum was also discussed at the symposium. John McCloskey of stuller inc. USA, presented results of a study in two common 950 platinum alloys, Microsegregation in Platinum-Cobalt and Platinum-Ruthenium Alloys. He and his co-workers calculated the microsegregation to be expected in cast alloys. Measurements on cropped sections of cast ingots by microprobe analysis showed localised concentrations of ruthenium from centre to edge of the primary dendrites varied between 2% and 6% in an alloy containing 4.8% ruthenium. For the 4.8% cobalt alloy, the figures varied between 4.3% minimum and 5.8% maximum. McCloskey used this data to calculate the partition coefficients and found broad agreement with those calculated from the phase diagrams. He noted that in the Pt-Ru alloy, the last liquid to freeze is depleted in ruthenium and is almost pure platinum (98% measured) whereas in the Pt-Co alloy, the cobalt concentration of the liquid increases during solidification.

He concluded that the non-equilibrium freezing characteristics of the two alloys were distinctly different and that this, together with the wider freezing range, may explain the better casting characteristics of platinum-cobalt alloys.

World View, in which he reviewed palladium as a jewellery metal. It included a potted history of palladium and some basic statistics on supply and demand. He noted that interest in palladium as a jewellery metal (as opposed to its use in white gold) started in China in 2003 and the Swiss began to use it for watches in 2005 as an alternative to white gold. Williams noted that pure palladium is too soft for jewellery use so alloys of 95% palladium have been developed (ie 950 fineness) that are harder and better wearing. The qualities of palladium as a jewellery metal include its preciousness as a member of the platinum group of metals, its natural bright white colour, good lustre and lack of tarnishing as well as its lower density. Like platinum, it is also rare and at 950 fineness, this high purity is attractive in the market.

Current ISO standards of purity are 950 and 500 finenesses. China has adopted 950 and 990, and in the USA 950 is favoured, as it is also in Germany and Switzerland. Currently, the UK assay offices have applied to have palladium recognised as a hallmarkable jewellery metal.

Williams noted that many 950 alloys are being developed and introduced to the market by alloy manufacturers, including Johnson Matthey, for both wrought and casting applications. Most are based on the palladium-ruthenium system with other alloying additions. He remarked that the one disadvantage is the high cost of refining palladium alloy scrap. He also made the point that proper, responsible marketing is required to ensure palladium does not cannibalise platinum sales. It is not a cheaper form of platinum.

Defect-Free Casting of silverI reported in Technical Bulletin Issue 3, the work carried out at the research institute of Precious metals & metals Chemistry (Fem) on computer

5

Top:

Barrie-John Williams from

Johnson Matthey, talking

about palladium

Above:

Delegate discussions

during a break


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rEpOrT: iNTErNaTiONal SaNTa FE SympOSium 2006

The investment casting of platinum was investigated by Apollonius Nooten-Boom II (Hean Studios, UK) in a presentation (given on his behalf by John Wright), Dynamics of the Restricted Feed Tree. He showed how metal flowed into the mould during casting and how improved fill can be obtained by use of a restricted feed system, which slows the feed of molten metal into the mould, contrary to conventional wisdom in the jewellery industry although not in the engineering industry.

other Papers of interest Andrea Basso, legor srl, Italy, spoke on Jewellery and Health: Recent Updates. This was a study on contact dermatitis in which 920 individuals were tested for allergies to metals commonly found in jewellery by skin patch tests using metal salts and metal discs (made of various carat gold alloys). The patch tests using metal salts showed positive reactions to several metals in the order (maximum number first): nickel, cobalt, palladium, potassium, gold, copper, mercury and silver, with platinum and zinc showing no positive reactions. Of the 266 patients positive to nickel, some 53% were not positive to other metals. The other 47% were also sensitive to cobalt chloride, palladium chloride and gold thiosulphate in that order. In the patch tests with metal discs, no type of allergic reaction was found in subjects not sensitised to nickel. However, it was noted that where nickel release values were below those limits of the EU Directive, some sensitised patients still showed allergic reaction.

Christopher Corti (CoreGold, UK) in Sources of Information for Jewellers discussed various sources and reference books on technical information. This included various websites including that of The Goldsmiths' Company, various handbooks and manuals by World Gold Council, Platinum Guild international, Johnson matthey and others

as well as jewellery journals and websites. This revealed a lack of up-to-date reference books on the metallurgy and properties of jewellery metals and their manufacturing technology. The Santa Fe Symposia books were considered important sources. Stewart Grice (Hoover & strong, UsA) discussed the diffusion bonding of difficult alloy combinations related to Mokumé Gane jewellery and focused on carat gold-platinum and gold-palladium combinations. A Goldsmith’s Experience in TIG Welding of Jewellery was presented by Kevin Lindsey (lindsey Jewellers, UsA) and showed its effective use in both small workshops and factories.

Martin Moser (otec Präzisionsfinish, GmbH, Germany) discussed the effect of machine finishing parameters on polishing of jewellery and how these can be used to optimise the finishing process. The investment casting of titanium jewellery was reviewed by Hubert Schuster (Jewellery Technology institute, italy) and the fundamentals of shotting and graining were reviewed by Joseph Strauss (HJe Company, UsA). Klaus Weisner (eVe GmbH, Germany) discussed the specifications of semi-finished jewellery materials and the problems that can arise if orders are placed with non-realistic expectations, based on his experience as an alloy supplier. The design aspect of jewellery was discussed by Barbara Berk (Designer, USA) who spoke about textile techniques such as weaving of wires, basketry and braiding in precious metals. Lastly, Valerio Faccenda (consultant, Italy) summed up the achievements of the last 20 years of the Santa Fe Symposium in terms of its contributions to the jewellery industry.

The conference proceedings are published in book and PowerPoint formats and are available from the organisers at www.santafesymposium.org The venue and date for the 21st Symposium, which returns to Albuquerque will be 23-27th May 2007.

Above:

Pd-Ga alloy. Longitudinal

section of tube drawn

to an outer diameter of

4.6mm after annealing

at 820°C

Below:

Palladium-Gallium

alloy. Microstructure of

tube drawn to an outer

diameter of 8.5mm

and subsequently

annealed. The welded

region has undergone

re-crystallisation even

though some marks of

the columnar grain still

remain. From Paolo

Battaini’s Santa Fe paper

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6

Under the current legislation, base metals generally cannot be combined with precious metals, except when base metals are

needed for technical reasons, for example, springs and pins for silver brooches. Furthermore, in an article comprised of two precious metals, the less precious metal must be in excess of 50% of weight of the article; the article is marked if it is wholly made of the lower fineness metal. The new legislation will abolish this 50% rule, and any combination of mixed precious metals will be allowed in an article.

The mixtures of precious and base metals will be allowed if there is differentiation by colour, or the word ‘metal’ is applied to the base metal part. The mixture of precious metals and non-precious metals will be allowed as before, and the minimum weights of the precious metal will still apply.A second amendment to the Hallmarking Act 1973 is to the exemption applicable to unhallmarked items of minimum fineness (800 standard) manufactured before 1920. Current legislation says that an article can be described as unhallmarked silver if it was made prior to 1920, however the amendment extends this date to 1950. The onus of responsibility still lies with the seller to prove the date and the standard of the article. While providing the date can be difficult without definitive provenance, proving the standard is easy - submit the article for hallmarking!

new members to the international Hallmarking ConventionThere is a new member that has ratified and joined the International Hallmarking Convention. The Republic of Cyprus’ entry came into force on 17 January 2007. The legal marks for Cyprus include a ship denoting gold standards and a fish for silver standards. Slovakia and Ukraine are expected to ratify the Convention within the next six months. For future changes to the Hallmarking Act 1973 and the International Hallmarking Convention, visit the Assay Office London website where these updates will be posted. www.assayofficelondon.co.uk

The leopard’s new spot in Hatton GardenOn 1 December, 2006, Assay Office London made history with the opening of its Greville Street premises. It is the first time in over 200 years that a fully operating assay office opened to the public. The Deputy Mayor of Camden, Councillor Dawn Somper, was the inaugural guest at the official opening. To commemorate the event, Councillor Somper was presented with a silver Christmas decoration made by Howard Fenn and inscribed using the laser at Greville Street. Since its opening, Greville Street has hallmarked over 50 packets a week, a testament to its immediate success. If Assay Office London’s valued customers intend to use the new sub-office for the majority of

HallmarkiNg updaTE:

briTiSH HallmarkiNg law amENdmENTS

responding to current trends in jewellery design and manufacturing, amendments to

the mixed metals provisions in the Hallmarking Act 1973 are changing imminently.

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Top: Cyprus gold mark

Above: Cyprus silver mark

Below:

From left to right -

Sir Jerry Wiggin, Prime Warden

of the Goldsmiths’ Company,

Deputy Mayor of Camden,

Councillor Dawn Somper,

Dr. Robert Organ, Deputy

Warden, Assay Office LondonMap of Greville Street Assay Office London


their hallmarking requirements, the Assay Office will arrange for sponsor mark punches to be transferred from the main office to the Greville Street office. Alternatively, customers intending to use both offices may order another sponsor punch at a reduced cost. For more information, please contact the registration department. T: 020 7606 8971 E: [email protected]

shedding light on the Black museumTo be, or not to be real…that is the question for The Black Museum. Within the last year, the Assay Office’s Black Museum, which is believed to be the largest collection of fake and forged silver articles in the world, has been re-catalogued and assessed by a team of silver specialists including Mr. Alastair Dickenson, Mr. Henry Willis, Mr David Cawte, Miss Lucy Morton and Miss Christina Reti, Assay Office London Development Officer. As the Assay Office has the power to seize and retain illegal objects, over the years it has amassed over 600 items that make up the Black Museum’s collection. Each item in the Black Museum was analysed by the team and its authenticity, legality and pending fate assessed.The Assay Office’s Black Museum includes articles seized in famously publicised fakes and forgeries cases, such as the Lyon and Twinam forgeries from the late 19th century. Reuben Lyon, an established London antique silver dealer, collaborated with Charles Twinam, a silversmith who used fake punches to mark modern pieces of silver, faking the date and maker. Through the combined efforts of the Assay Office and various police forces, over 250 objects were seized from Lyon’s shop and Twinam’s workshop in 1898-1899. The majority of these articles remain in the Black Museum. Nonetheless, the Assay Office’s advisory body on the authenticity of antique silver, the Antique Plate Committee, reviews at least one object annually that is linked to Lyon and Twinam.The Lyon and Twinam fakes are just one example of the sorts of illicit objects made by unlawful silversmiths. Other objects in the Black Museum bear transposed hallmarks, often done to increase an article’s value through false age or pedigree. A large percentage of the Black Museum includes objects with illegal additions and alterations, either with a change in the article’s use or not. The most common example of an illegal alteration with a change in its use is a

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17th century tankard converted into an 18th or 19th century style coffeepot. Although most of the pieces in the collection are dubious at best, they provide invaluable insight into the world of crime and the skills of silversmiths. Selected items from the Black Museum will be on view in the Assay Office in the near future.

Fakes and Forgeries seminarEducating the public on the various types of fakes and forgeries is an important role undertaken by Assay Office London. On 24 January 2007, the Assay Office held a Fakes and Forgeries seminar for 50 members of the public and the trade. The full-day seminar included a lecture by keynote speaker, Alastair Dickenson, and hands-on sessions run by recognised silver specialists. Due to popular demand, the Assay Office is holding another seminar on 15th June 2007 at Goldsmiths' Hall, one on 22nd June 2007 at Goldsmiths' Hall in Edinburgh, as well as other locations throughout the United Kingdom and North America later in the year. Interested participants are encouraged to contact the Assay Office as soon as possible to ensure availability and for further information. www.assayofficelondon.co.uk

christina retiAssay Office London Development Officer

goldsilverFull hallmark (silver)

Part hallmark (gold)

Part hallmark (platinum) platinumgold

Full hallmark (gold)

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Tankard converted

into a coffeepot

Above:

A Lyon and Twinam

pierced basket with

counterfeit marks from

fake punches

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The new hallmarking legislation - examples of hallmarking of mixed metals

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It was produced after consultation with 100 representative jewellery, silversmithing and allied businesses in 2005 including focus groups and

one-to-one interviews. In 2006, The City Fringe Partnership along with its partners the london Borough of Camden and The Goldsmiths’ Company secured £3 million to invest in a range of JSIP projects.The first six initiatives being promoted include projects covering technology and bespoke industry-led training, skills and industry awareness days for the community living near Hatton Garden, an export project, an executive forum and a feasibility study for staging a London Jewellery Design Week.

1. Grants and Workspace opportunities – Hatton GardenLondon Borough of Camden, supported by the Change-Act-Share project, is using its planning policies to secure funding for equipment costs and new workspace for jewellery manufacturing business in the Hatton Garden area. Funds for fit-out are currently available for jewellery manufacturing units operating for less than three years based in, or moving to, the Hatton Garden area. Applicants can apply for two thirds of the cost, the minimum grant is £2,000 with the amount depending on the number of employees in the business. Companies purchasing new technology are particularly encouraged. A further £350k will be available from August 2008. This fund will be able to support jewellery manufacturing businesses beyond the Hatton Garden area provided they are based in the London Borough of Camden. Available also from Autumn 2008 will be 42 workshop units of 230sq ft. Priority will be given to Hatton Garden craft manufacturers who have less than three years to run on their current leases and/or are in buildings at risk of development.Contact: W: [email protected] T: 020 7974 2271/3519

2. export Assistance for london JewellersDesigner-makers and jewellery firms in the Greater London area are being offered the chance to expand their export horizons thanks to a new two-year project, London Jewellery Exports. The project is being organised by the British Jewellers’ Association funded by City Fringe Partnership and the london Development Agency, through the Jewellery Sector Investment Plan, with the collaboration of UKTI.Eligible companies will be provided with information, advice and in some cases financial incentives to assist them with their exporting activities. The programme will include sponsored visits to trade shows such as Inhorgenta in Munich, the New York International Gift Show and Iberjoya in Madrid. There are also

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The Jewellery sector investment Plan (JsiP) is a regional programme aimed at making

the london jewellery and allied industries more competitive.

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Above and Opposite:

The JSIP project

launch event held

at Goldsmiths’ Hall

in February 2007

attracted more than

170 members of the

industry

plans to explore less well-known markets such as Scandinavia, India and the United Arab Emirates and for a private exhibition of London jewellery in Dubai.The organisers are looking for suggestions from London jewellery businesses as to which markets they would like to research and would welcome calls from all interested parties. For further information contact Lindsey Straughton:T: 0121 237 1112 W: [email protected]: www.londonjewelleryexports.com

3. Feasibility study for london Jewellery WeekOne of the key demands of the JSIP is a consumer-facing London jewellery event, which will focus on the best of London’s jewellery products and designers. UK consumer spending on jewellery rose by 28% during the period 1998-2003, yet while other luxury markets and new luxury accessories brands are opening in London, the London jewellery industry is not reaping the rewards of future potential growth. A jewellery week has been proposed by the industry as a way of helping to access the growth in the marketplace. The events will be desirable, glamorous and aspirational and will benefit from celebrity endorsement where relevant. For further information contact:W: www.change-act-share.org.uk

4. Bespoke Technology & TrainingHolts Academy of Jewellery, Metropolitan Works and the Jewellery Industry Innovation Centre (JIIC) have formed a partnership for the support and development of designers, makers and manufacturers within the trade through technology and specialised training. Through one-to-one assessment sessions, specific skills and training needs can be analysed, both practical and in business. Particular attention will be placed on areas of production that add value and increase efficiency.

5. london Jewellery FirstThe call for the industry to have a ‘voice’ of its own came out of the Jewellery Sector Investment Plan (JSIP) process. Members of London Jewellery First (LJF) were chosen through a competitive interview process that concluded in April 2006. The main purpose of LJF is to support and direct a period of change within London’s industry to help make it more competitive, sustainable and design-led. London Jewellery First’s mission is to work towards engaging the London jewellery and allied trades; acting as a catalyst to create a new positive culture, raise its profile and drive the industry forward. For

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further information contact Fiona McKeith, Jewellery Sector Investment Manager:T: 020 7974 3519W: [email protected]

6. Business Development for DesignersHolts Academy of Jewellery and Palmer Hamilton Partnership Ltd. (PHP) are delighted to announce the launch of a new project for the jewellery sector, Future in the Making. This two-year action research project will link 12 established contemporary jewellery designers with manufacturers, product developers and retailers to provide an integrated approach to product development, business growth and commercial sustainability. For further information contact Lee Lucas: T: 020 7405 0197E: [email protected]

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sir John Cass Centre for silversmithing and Jewellery - short Course Programme The Sir John Cass short course programme for 2007 will include: Stone Setting with Tony Tigg, Working with Wax - Mark Rouse, Introduction to Hand Engraving - Wayne Parrott, Lost Wax Casting - Claire Black, Enamelling on Silver - Jane Short, Working with Stone with Charlotte de Syllas, Mokume Gane - Alistair McCallum, Working Enamel Panels - Elisabeth Turrell, Working with Resin - Dawn Gulyas, Designs on the Future: Innovating - D Goodwin and A Monroe, Anti-Clastic Raising - Beaulagh Chapman, Scoring Folding and Bending - Mary Ann Simmons, Sinking, Dishing and Peening with Adrian Hope, Granulation - Linda Lewin, Polishing for Silversmiths - Brian Marshall. For more information and a brochure please contact: Alan CraxfordT: 020 7320 1926 or email: E: [email protected]

school of Jewellery, University of Central england - short Course ProgrammeThe School of Jewellery in Birmingham has over 50 courses in its 2007 short course programme. All are designed to offer training opportunities to those involved in the jewellery or other creative industries to develop existing skills, or to learn highly specialised new techniques in a short time frame of between one to five days. In keeping with its commitment to excellence, several respected international tutors will be contributing to its wide range of courses. A selection of these will include: Pattern and Colour: colouring jewellery with cold enamel, Mokume Gane and colouring and forming anodised aluminium jewellery, Silversmithing: design and formation, anti-clastic raising, hydraulic die forming and spinning, CADCAM: 1 day, 3-day or 6 evening session CAD courses on a variety of software programmes including ArtCAM Jewelsmith, JewelCAD, Rhino and Solidworks. Rapid Prototyping: An introduction to CAD/CAM (3 day course). A selection of new courses for 2007 will include Creative and Experimental Surfaces in Enamel with Elizabeth Turrell, Diamond Awareness 1-day course with Grenville Millington (FGA), Keum-Boo, Enriching Silver Surfaces with Kye-Yeon Son. Keum-Boo is the traditional Korean surface embellishment technique of fusing 24K gold foil onto silver, Hand-Made Silver Chains with Jinks McGrath and Polishing for Jewellers and Silversmiths with Stephen M Goldsmith. For further information or to request a brochure, please contact:T/F: 0121 248 4584 or email E: [email protected]

Holts Academy of JewelleryThe Holts Academy is re-locating to dedicated premises. The new premises, currently receiving a full renovation and custom fit-out, will triple the capacity

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Below:

Diamond grading

at Holts Academy

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Mokume gane with

Alistair McCallum at

Sir John Cass

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Students at one of the

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In recent years a number of ‘new’ sterling silver alloys have become available in the UK and elsewhere

in the world that could represent real opportunities for workers in the craft and industry. Many claims have been made in relation to these including 'tarnish resistance' and reduced incidence of ‘firestain’ during manufacture. However, questions remain and a lack of understanding of good practice in terms of their application may limit their long-term value and adoption within the industry.

As part of its investigations, the Goldsmiths’ Company is proposing to undertake a practical review of two of the alloys commercially available here in the UK with the aim of gaining a better understanding of their application in a workshop environment.

The Company is seeking the assistance of five workshops (ranging in size from designer-makers to larger workshops) to undertake a series of tests using the alloys. It is envisaged the trials will take a week to complete with all materials provided and financial recompense given.

It is anticipated that this will lead to the publication and dissemination of the results through seminars, papers, a Goldsmiths’ Company technical report and the Technical Bulletin. If you are interested in participating in this ground-breaking project, please contact Peter Taylor, Director Technology & Training at: [email protected]

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prOJECT aNNOuNCEmENT:

N E w S T E r l i N g S i l v E r a l l O y SThe 'Holy Grail' of the silver industry remains a truly tarnish-

free silver alloy that maintains the colour, feel and working

characteristics of normal sterling silver alloys.

for teaching with two large workshops, a CAD suite and gallery space. The building work is estimated for completion by the end of April. During this period, all training with the Academy will continue as normal at 98 Hatton Garden. In addition to existing training courses, Holts offer courses on computer aided design and manufacture where students receive IT training tailored for the jewellery industry including the chance to export models to rapid prototyping machinery. Other courses scheduled for 2007 include Laser Welding, Diamond Grading, Simply Setting and the Wonders of Wax. For further information on new and existing courses, please contact Lee Lucas: T: 020 7405 0197 E: [email protected] W: www.rholt.co.uk.

newham College of Further education - The Jewellery manufacturing Pre-Apprentice CourseThe Jewellery Manufacturing Pre-Apprentice Course is a new course designed for those wishing to pursue a career in the industry. For three days a week over eighteen weeks, the course will provide a practical introduction to the industry and to the design and craft skills needed in jewellery manufacture. The course is part of a new apprenticeship programme aimed at supporting employment in the jewellery industry. The next course is scheduled to start in September 2007. For further information:T: 0845 6504244W: www.cipsonline.com

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CalENdar OF EvENTS

An up-to-date list of events and exhibitions hosted by the Goldsmiths’ Company can be found on the website under the What’s on section.

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M a y 2 0 0 712th-16th MayVicenzaoro springFiera di Vicenza, Vicenza, ItalyIncludes the machine exhibition, Oromacchine.www.vicenzaorospring.it

31st May-14th Julyrising starsGoldsmiths’ Hall, LondonThis exhibition will focus on work by selected young silversmiths and jewellers considered to be among the most accomplished and skilled in their field. Admission free.www.thegoldsmiths.co.uk

20th-23rd May21st santa Fe symposium on Jewellery manufacturing TechnologyAlbuquerque, New Mexico, USAThe Santa Fe Symposium remains the world’s most important technical conference on the art and science of jewellery manufacturing. (See Issue 2, 2005 Report, pp14-15.)www.santafesymposium.org

J U n e 2 0 0 71st-5th JuneJCK show las VegasSands Expo and Convention Center & The Venetian Hotel, Las Vegas, USAThe JCK Show Las Vegas is designed to serve the worldwide jewellery industry by offering the most comprehensive and complete buying and selling opportunities on a business-to-business basis. www.jckgroup.com

J U l y 2 0 0 73rd-7th July5th international Jewellery symposiumSaint Petersburg, Russia

Jewellery technology symposium.www.j-symposium.ru

4th-5th JulyTechnology event and seminarsThe School of Jewellery, BirminghamTwo-day technology awareness event organised and sponsored by the Jewellery Industry Innovation Centre, to coincide with its 10th birthday celebrations. It will feature high quality speakers, both technical and design-oriented presenting their thoughts and ideas on ‘Designing for Technology’[email protected]

5th-8th Julynew Designers exhibitionBusiness Design Centre, Islington, LondonNew Designers is the foremost event in graduate design showcasing the work, energy and talent of some 4000 young designers.www.newdesigners.com

6th-7th JulyConnect: ABDs international Conference and eventLakeside Conference Centre, Aston University, BirminghamA two-day event organised by the Association of British Designer Silversmiths. Hosted by Matteo Alessi, it will examine ways in which new technologies and design can combine with traditional manufacturing skills to provide an edge in a highly competitive international market.www.connect07.co.uk

11th-12th Julyrapid manufacturing 2nd international ConferenceSir Dennis Rooke Conference Centre, Holywell Park, Loughborough UniversityThis conference will feature a state-of-the-art mixture of world-leading industrial applications and cutting-edge academic research currently being undertaken into RM - the use of additive layer manufacturing techniques for end-use parts.www.rm-conference.com

s e p t e M B e r 2 0 0 724th September-7th October (closed Monday 1st October)The 25th Goldsmiths’ FairGoldsmiths’ Hall, London2007 sees Goldsmiths’ Fair celebrating its silver anniversary and in celebration of this milestone will extend to two weeks. www.thegoldsmiths.co.uk

2nd-5th Septemberinternational Jewellery londonEarls Court 2, LondonThe ultimate UK trade event for buying, selling, networking and keeping abreast of latest jewellery designs and innovations.www.jewellerylondon.com

15th-19th SeptemberVicenzaoro Autumn Fiera di Vicenza, Vicenza, Italywww.vicenzaoroautumn.it

14th-16th SeptemberClaspDenver, Colorado, USAA new education and networking conference specifically designed to serve small manufacturers, metalsmiths, designing jewellers and bench jewellers. www.claspconvergence.com

26th-27th SeptemberTCT Conference and exhibitionRicoh Arena, CoventryTCT 2007 is the UK’s No.1 Rapid Product Development & Manufacturing Exhibition and Conference. It is the only UK event focused on providing solutions for accelerating products to market.www.time-compression.com

D e c e M B e r 2 0 0 75th-8th December euromoldExhibition Center Frankfurt/Main, GermanyWorld Fair for Mouldmaking and Tooling, Design and Application Development.www.euromold.com

Documents

the goldsmiths’ company TECHNICAL BULLETINtechnical-journal.thegoldsmiths.co.uk/wp-content/uploads/...reputation of the Goldsmiths’ Company in jewellery manufacturing technology