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DESALTING OF STONES BY MEANS OF ION EXCHANGERS

DOMASLOWSKI, WIESLAW AND TOMASZEWSKA-SZEWCZYK, ALINA

Institute for Conservation and Restoration of Cultural Property, Nicholas Copernicus University, Torun, Poland

SUMMARY

The study refers to practical use of ion exchangers for desalting of porous stones. By application of the ion exchangers a composition was prepared characterised by high effectiveness in cumulation of water soluble salts showing capability to perform a number of various conservation requirements. Ion exchange occurring in strongly acidic and strongly basic mixture takes place in environment of 6.6 pH value. Yet round the grains relevant media are formed. Acidic medium due to cation exchangers brings about spotlike decomposition of calcium carbonate at the contacting area of the stone therefore application of ion exchangers requires strict observation of pertinent procedures.

1. INTRODUCTION

The most frequent method used by conservators for removal of water soluble salts is desalting by free migration into widened medium. This action may be performed by materials with extremely large area ratio such as cellulose dust, cellucotton or cotton wool laid over stone as compress. In such case salt cumulation process takes place by mechanical mechanism. In adverse outer environmental conditions there may occur possibility for re-entry of salt from the lining into the stone. This drawback may be avoided by using desalting ion exchanger material or substance. In such circumstances cumulation process alters its action into combined chemical and physical activity and salt migration will take place in one direction. Stone desalting by physico-chemical process may be compared to water deionization of ion exchangers mixed in column process 1 in which solution leaks through immobile bed of mixed cations and anions exchangers placed in a column. The influent, by displacement among the exchanger grains gives away ions. As the solution in the column undergoes displacement their concentration drops. If the bed has sufficient quantity of ion exchanger ready for exchange of all ions the effluent should not contain salt, but equivalent quantity of H+ and OH- ions derived from ion exchanger. However in most cases it contains unexchanged ions although ion exchangers still have free ion exchanging groups. This is due to the fact that the number of ions that a given column is capable to exchange in definite working conditions, that means its break through capacity2

, is less from the total column capacity. This is dependent on the solution flow rate and factors influencing rate of ion exchange. In desalting process of stone the function of a column is performed by the ion exchanger compress. The process itself includes a few stages. The stone first undergoes saturation with water which by penetration of capillaries dissolves gradually its salts. Thereby a slow ionic diffusion into the outer environment takes place. As water evaporation from the lining surface gradually sets in then solution is displaced by capillary action in the compress direction. Hence in the lining chemisorption process takes place, this involving ion exchange between the solution and the ion exchangers until an

equilibrium state has been established. At the beginning materials with insignificant ion-exchange capacity had been in use. These were clay minerals. Nowadays synthetic organic ion exchangers are in wider use.

1 W.Domastowski, M.Zyzik, Badania nad zastosowaniem jonit6w do odsalania kamiennych obiekt6w zabytkowych, Acta Universitatis Nicolai Copernici, Zabytkoznawstwo i Konserwatorstwo V Nauki Humanistyczno-Spoteczne, fascicle 52, Torun 1973, p.218. 2 O.Samuelson, Jonity w chemii analitycznej, Warsaw 1958, pp.60-1.

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In the process a mixture of cations and anions must be used this allowing to create desirable

conditions for combining the anions and cations of the soluble salts. The ion exchangers have to

show the characteristic of strong acids and bases and to have considerable exchange capacity so that

the exchange rate and exchange capacity are significant. Not knowing the working exchange capacity

it is advisable to use access ion exchangers, so that all ions getting into the lining are replaced by the

ion exchangers. To avoid formation of salts as by-products used cations must have ion replaceable

hydrogen and cations - hydroxyl group. Ion exchange should take place in neutral medium that may

by prepared by use of suitable mixture of anion and cation exchangers3

. This requirement must be

strictly observed during desalting of minerals that are not resistant to acids, such as calcite, as it will

be subject to decomposition in medium formed by strongly acidic cation exchanger. Such medium

should not be strongly alkaline for there will occur hindrance in anion exchange as increase in pH

value leads to considerable belittling of dissociation of basic groups. Small grain ion exchangers

should be used. This will ensure fast and effective ionic exchange and creation of desirable desalting

lining.

In an earlier work4 treating this subject of application of ion exchangers for desalting porous stones

their action upon calcium carbonate and their effectiveness in cumulation of water soluble salts was

studied. These investigations were carried out with strongly and moderately acidic cation exchangers and

moderately basic anoin exchangers. Too coarse granulation of ion exchangers hindered formation of

the compress therefore they were mixed with cellulose dust.

Relevant investigations led to conclusion that cation exchangers decompose calcium carbonate and

Ca2+ ions migrate into the lining. This decomposition is decreased when mixture of ion exchangers is

used. Presence of sodium chloride showed increased solubility of calcium carbonate in presence of

electrolyte having no common ions. In case of 'Pii'lcz6w' limestone salted with 10% sodium chloride

solution desalting by means of ion exchanger compress after three cycles amounted to about 93%.

In practice ion exchanger type linings were used in Poland for desalting the tomb monument

belonging to the Rakowiecki Cemetery in Cracow. This object was subject to desalting by forced salt

migration into widened medium. It was placed in water to the height of about 1 Ocm and protected with

plastic foil so that water could evaporate from the undipped part. This surface was covered with ion

exchanger compress. Because of poor sticking to the stone it was held by special bandage. This

method proved very effective. Initial salt content was 8%. After this treatment this was lowered to only

0.5%5

. This desalting approach was also used for wayside shrine from Prudnicka £1 ka (Prudnik Meadow) near Opole.

Trials with desalting by ion exchanger method were used also by Lehmann6. He modified paper pulp

with ion exchangers in order to make it selective and to prevent engaging the integral stone

constituents. He selected ion exchangers with full consideration to chemical composition of salts.

2. THE AIM AND SCOPE OF TESTING

The aim of testing is checking usability of ion exchangers for desalting limestones by the method of

salt free migration into the widened medium. Its scope included elaborating proper desalting

compress with neutral relation to calcium carbonate and good adhesion to the stone, this enabling

applying linings upon surfaces with large angular bends and also testing its effectiveness in water

soluble salts cumulation and comparison with desalting efficiency by more frequently used methods by conservators, that means by cellulose dust and cellucotton compresses.

3 W.Domaslowski, M.Zyzik, op.cit., p.218. 4 ibid., pp.218-9. 5

B.Susczyk, J.Dorau, Dokumentacja konserwatorska pomnika nagrobnego z cmentarza Rako-wieckiego w Krakowie, copy, Torun 1980/81, p.7.

~ J.L~~ann, ~rzyklady zasol~nia i ~ania kamienia w zabytkach, in Konserwacja kamienia w architekturze 1 rzeYb1e, Btbhoteka Muzealructwa 1 Ochrony Zabytk6w, series B, vol.XIX, p.160.

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3. CHARACTERISTICS OF MATERIALS USED FOR TESTING

Stone:

• 'Piiicz6w' limestone - cubes 5x5x5cm, plates 30x10x5cm • D6bnicki 'marble'

S3awniowicki marble

Table 1. Properties of Stones Used in the Testing7

Stone Characteristics Water Absorption Open Porosity .(%) (%)

'Pincz6w' stone lithotonic limestone 17.05-18.99 36.67-37.38 Debnicki 'marble' black closely packed limestone, black (touchstone) colour is due to bituminous compounds,

small calcite vains, small grain, lack of resistance to atmospheric effect, humidity and atmospheric oxidation of bitu-minous compounds leads to loss of 0.18-0.32 0.4 polish and even its colour

Slawniowicki marble crystalline coarse grain structure, not - dark blue, regular, colour derived from biotite, strea15Y....9.rade resistance to atmospheric effect 0.15 1.1

Ion Exchangers: In the testing German ion exchangers were used made by VEB Fabriken Wolfen - strongly acidic cation exchanger Wofatit KPS and strongly basic anion exchanger Wofatit SBW. The cation exchanger is based upon the resin styrenedivinylobenzene with integrated sulphonic groups having granular form with amber colour with size ranging from 0.3 to 1.2 mm. Its total exchange capacity is 1.8 Eq/dm3 and working exchange capacity is from 1.0 to 1.6 Eq/dm3

. Anion exchanger Wofatit SBW is polystyrene resin with incorporated tetraordinate trimethyloamonium groups in the form of orange granuls with grain size ranging from 0.3 to 1.5mm. Its total exchange capacity amouning to 0.9

Eq/dm3 and working capacity 0.5 Eq/dm3.

Delivered Wofatit KPS cation exchanger and Wofatit anion exchanger required applying elusion

process before using them in testing.

Materials Used for Modification of the Compresses: For modification of the compresses based on the ion exchangers the following materials were used:

• colloidal silica "Aerosil" - by Degussa, Austria,

• white technical grade talc, in order to render the compresses thixotropic and to enhance sorption effect, • cellulose dust - this was mixture of cellulose obtained from coniferous and deciduous trees in the

ratio 1 :1 , occurring as white loose powder, sold in rolled up form by the Toruiiskie Zak3ady

Material6w Opatrunkowych, Poland, in order to improve compress adhesion to wet and dry stone and to increase overall capacity, • 0.25% and 0.5% glue solution for wall paper based on methylcellulose- Legocol GmbH, Germany,

used as binding agent.

Comparative Materials: • cellucotton in flaked state - Toruiiskie Zakfady Materiaf6w Opatrunkowych, Poland

• cellulose dust (mentioned above)

Samng Solution: • 5% and 10% sodium chloride

7 S.Kozlowski, Surowce skalne Polski, Warsaw 1986, pp.119, 123, 124-5, 185, 187, 198. Kamienie budowlane i drogowe, pod red. M.Kamiefiskiego i W.Skalmowskiego, Warsaw 1957, pp.122, 131-2.

M.Karniefiski, Ska3y budowlane w Polsce, Warsaw 1949, p.86.

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4. EXPERIMENTATION

4.1. Adhesion Evaluation of the Compress to Wet Stone and Ease of Detachment

After Drying. Compress pH Determination.

4.1.1. Methods of Investigation 'Piiicz6w' stone plate pieces, measuring 30x1 Ox5cm were saturated with water by capillary elevation. The underlying assumption was that testing should be carried out on one surface (30x10cm),

therefore 5 other plates were insulated with polyethylene foil. Regenerated ion exchangers were

mixed in the ratio 3 parts by volume of the anion exchanger to 1 part by volume with the cation exchanger (this proportion was determined by the exchange working capacity of the ion exchangers). The compound of cellulose dust with distilled water or 0.25 and 0.5% methylcellulose solution in the

volumetic ratio 100g to 1dm3 was prepared by a mixer (straight hand type). Mixing was kept up for about 10 minutes until getting uniform mixture. Next ion exchangers were added in required volume

proportions. The talc or colloidal silica were mixed with ion exchangers by spatula, adding gradually 0.25% or 0.5% glue solution based upon methylcellulose until obtaining uniform consistency allowing ease of applying compresses. The lining compositions are specified in the Table 2.The desalting compound was applied with spatula in layers up to about 2cm thick. After laying up the samples were inclined under varying angle. Next pH determination were taken using indicator paper with narrowed

pH 6.2-8.2 range. The samples were than put off for drying. Evaluation was carried out by observing compress adhesion to both wet and dry stone surface. After drying out the samples were evaluated visually for shrinking and staining of stone surface. This

evaluation comprised both difficulty in preparing the lining and ease of removal after desalting

procedure. Drying took place in prevailing atmosphere with 58-80% humidity and in temperature range from 12

to 22°C.

Table 2. Lining Compositions Subject to Evaluation

Deno- Filler used Volume Ratio Methylcellulose Water or tation Filler/Ion Solution Methylcellulose

Exchangers Quantty (%) (dm3/100g)

A 1 :0 - 1 B 1 :1 - 1 c 2:1 - 1 D cellulose dust 1 :2 0.25 1 E 1:2 0.5 1 F 1: 1 0.25 1 G 1:1 0.5 1 H 1 :2 0.25 0.64 I colloidal silica 1 :2 0.5 0.64 J 1:1 0.25 0.64 K 1:1 0.5 0.64 L 1 :2 0.25 0.012 M talc 1 :2 0.5 0.012 N 1 :1 0.25 0.012 0 1: 1 0.5 0.012 p - 0:1 0.5 0.05

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4.1.2. Results

Results are presented in the Table 3.

Table 3. Desalting Effects of Particular Compresses (Phot 1-3) Deno- Desalting Compress Adhesion to Wet Behaviour in DryingEase of Removal tat ion Preparation Stone and Soiling Effect of pH

the Stone Surface A easy composition is easy relatively large shrinkage, good 6.6

in handling and adhesion to dry stone, rather hard for shows good adhesion removal does not stain stone surface

B as above as above lower shrinkage than A, good adhesion as above to dry stone, easier in removal than A, does not stain stone surface

c as above as above as above as above D as above as above substantial shrinkage after drying out as above

visible net of cracks, good adhesion to dry stone, easy to remove, leaves no soili~ or stains on stone surface

E as above as above as above as above F as above as above substantial shrinkage, after drying out as above

visible net cracks, good adhesion to dry stone, difficult to removal because cellulose fibres get stuck to stone surface

G as above as above as above as above H as above good, may be applied in the last days of drying it fell off,

with putty-knife, coloration of stone surface by shows thyxotropic methylcellulose behaviour

I as above as above as above as above J as above as above as above as above K as above as above as above as above L as above as above after drying visible net of cracks, some as above

whiting hard for removal with rather fatty touch

M as above as above as above as above N as above as above as above as above 0 as above as above after three hour drying period cracks as above

appeared, after three days middle part of the compress fell off, whiting left difficult to remove

p as above good after three days it fell off as above

4.1.3. Discussion on the Results No matter what filler used the compresses are easy to prepare and show good adhesion to wet stone. By incorporation of colloidal silica and talc the linings denoted from H to 0 acquired thyxotropic

properties. All compresses showed weak acidic reaction - pH 6.6. Cellulose dust compress is characterised by high shrinking effect and outstanding adhesion to dry stone - it is therefore hard to be removed. Yet it does not leave soiling effect on the surface.Addition of ion exchangers belittles shrinkage and strong adhesion to the surface. The compresses based on

ion exchangers with cellulose dust pasted with methylcellulose solution are characterised by excellent adhesion to dry stone; but show large shrinkage, with evident cracks allover after drying out. Addition

of binder in considerable concentration results in cellulose fibres sticking to the stone surface, this

leading to difficulty in removing from stone. The desalting compositions having colloidal silica, despite

addition of binder - 0.25% and 0.5% methylcellulose solution, got cast off before stone drying out.

Talc used as filler tends to increase contraction of the compress composition. Cracking of the lining O

appeared already in the first few hours of drying. Moreover talc leaves whitening stains that are hardly

removable. The compress compound having 0.5% methylcellulose solution underwent shedding

before stone drying out.

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4.1.4. Conclusions Out of the 15 desalting linings based on ion exchangers two namely B and C (referred to now as the

compress I and the compress II) were selected for further testing. They are the only onces showing many positive features. They are easy to prepare and handle and may be applied even on highly

inclined surfaces as they show good adhesion to both wet and dry stone. Also noteworthy is their ease

for removal and lack of stone staining effect.

4.2. Testing Desalting Compresses Destructive Influence (Action) on Calcium Carbonate

4.2.1. Method of Investigation The prime aim of the experiments was showing effect of ion exchangers on polished surface of

Debnicki ·marble'. Upon it compresses were laid made of anion exchangers, cation exchangers,

mixture 3 to 1 of the two ion exchangers, cellucotton, cellulose dust and the compresses I and II and moreover compress I with 3 and 5 undertayers of cellucotton. Similarly the S3awniowicki marble was

laid with compresses of anion exchangers, cation exchangers, cellucotton, cellulose dust and the

compress I without and with 3 underlayers of cellucotton. After drying out they were removed, and the stone was washed with water, dryed and the condition of polish evaluated. Testing was also

conducted using diffrent method. Part of Slawniowicki marble beams with polished surface was placed for three days (72 h) into beakers in distilled water, cation exchangers, anion exchangers and mixture of the latter (cation:anion exchangers ratio 1 :3) and the Debnik 'marble' was acted on only

with distilled water. After removal, when the test pieces got dried their surface condition was examined. In both cases only unaided visual magnifying glass and binocular microscope examinations were carried out.

4.2.2. Results

Results are presented in the photographs 4-6.

4.2.3. Discussion on the Results

Cation exchanger compresses led to destructive action in all stone surfaces. Point type and semispherical pitting (largest were evident in touchstone). Action of acidic cation exchanger environment caused disappearance of edges and shallow irregular pitting in the Slawniowicki marble surface. Anion exchanger compresses caused only delicate dulling on polish of the 'Debnik' and

Slawniowicki marble. Action of the cation and anion exchanger mixture in the relevant ratio 1 :3 led to surface dulling in Slawniowicki marble and in case of touchstone there appeared also rare but sharp pittings. The compress I caused irregular, strong dulling and few dispersed pittings in 'Debnik', yet in the marble delicate dulling and single shallow pittings. Action of the compress II upon touchstone was much the same as that of the compress I.

Destructive characteristics of the compresses I and II on marble surface stirred up seeking better solution. Therefore it was decided to use intermediate layer consisting of 3 and 5 cellucotton leaves.

The compress I with an intermediate layer of three cellucotton layers caused irregular loss of polish on 'Debnik' and delicate local dulling on Slawniowicki marble. On using thicker undertayer the touchstone showed weaker dulling effect. Most frequently used compresses by conservators -cellucotton and cellulose dust led also to dulling an stone surfaces. Cellucotton caused also dulling on

'Debnik' surface, whereas cellulose dust led to evident strong loss of polish upon touchstone surface and intensive dulling on the Slawniowicki marble. In case of marble surfaces loss of gloss was also caused by distilled water.

4.2.4. Conclusions

Described tests show that acidic environment created by the cation exchangers leads to

decomposition of calcite in boundary areas of its grains. In case of anion exchanger some small effects in gloss are due to varied stone resistance to water action. This phenomena is also evident in

case of applying ion exchanger mixture and the compresses I and II . Bigger proportion of cellulose

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dust in the compress does not ensure betterment in surface staining. Staining was decreased by applying intermediate layer of cellucotton. The thicker it is the lesser destructive effects was evident on the Debnicki 'marble' surface. It ought to be added that such materials as cellucotton and cellulose dust also brought in dulling of stone surface. This effect was more evident in case of cellulose dust. Most likely this is due to its strong adhesion to stone and extensive contraction occurring during drying, and also this may be ascribed to longer water action (compresses made on cellulose dust dry at slower rate as they contain more water). Addition of ion exchangers to cellulose dust weakens destructive effect.

4.3.Desalting Effectiveness Testing by Compresses Based on Ion Exchangers and by Traditionally Used Materials

4.3.1.Method of Investigation In the tests 'Piricz6w' limestone cubes with 5cm long edge were used. The test pieces were cleaned of dust and submitted to desalting treatment in static bath for seven days. Each day water was replaced. Water absorption by weight of the test pieces varied from 14.31 to 22.87%; for testing cubes with water absorption ranging from 17.05 to 17.95% were selected, and these were soaked with 5% sodium chloride solution, and cubes with water absorption ranging from 18.06 to 18.99%; the latter were soaked with 10% sodium chloride solution. The test cubes were soaked by capillary elevation and then the salting solution was added. After four days they were removed and dried in 105°C and percentage salt content was determined. The cubes were placed on Petri's balance pans and saturated with distilled water by capillary elevation. On five cube walls the following desalting compresses were laid: • cellucotton (1 O layers), • cellulose dust prepared with water (1 OOg in 1 dm3 of water - applied compress thickness was about

1cm), • compress I - cellulose dust prepared with water, using 1 OOg of dust for 1 dm3 of water and addition

of ion exchangers in volumetic ratio 1 :1, anion to cation exchangers in volumetic ratio 3:1

(compress thickness about 1 cm), • compress II - cellulose dust prepared with water (100g/1dm3 of water) and addition of ion

exchangers in volumetic ratio 2:1, and anion to cation exchangers in volumetic ratio being 3:1

respectively (compress thickness about 1 cm). The test pieces were dried in the temperature range 13 to 25°C and relative humidity 60 to 80%. Each day the cubes were weighed. After finishing desalting process, i.e. after getting constant weight in these conditions (depending on the compress this took 6 to 12 days) desalting compresses were removed and then the cubes were dried in the temperature 105°C and weighed on the technical scale.

Desalting effectiveness was determined by the formula:

where: E - desalting effectiveness (%) Z1 - percentage salt content after salting (%) Z2 - percentage salt content after desalting (%)

Test results are derived from five repeated experiments.

4.3.2. Results Results are compiled in the Table 4.

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Table 4. Desaffing Effectiveness by Using Various Methods

Cellucotton

Cellulose dust

Compress I

Compress II 10 1.97

Desalting Effectiveness 100

90

80

70

80

60

40

30

20

10

0 TEST PIECES SATURATED WITH 5% Nae I SOLUTION

4.3.3. Discussion on the Results

TEST PIECES SATURATED WITH 10% NaCl SOLUTION

OCELLUCOTTON

CCELLULOSE OUST

El COMPRESS I

•COMPRESS II

Desalting effectiveness shown by the cellucotton compresses was lowest and the mean result for

cubes soaked with 5% and 10% sodium chloride solution amounted to 60%. For cellulose dust the relevant result was much better - amounting to nearly 91 % . Similar desalting capability was shown by the compresses I and II , amounting to 97%. Desalting capability of the cubes saturated with more highly concentrated salt solution reached the mean level of 84%. Probably the compress capacity was too low to combine and adsorb salt appearing at high concentration level.

4.3.4. Conclusions

Compresses based on ion exchangers proved equally efficient in cumulation of water soluble salts as cellulose dust. This desalting method is more effective (by about 36%) than cellucotton. With the increase of salt content in limestone there appears a drop in effectiveness of used compresses. At high salt concentration level such treatment must be repeated.

4.4. Final Evaluation of the Testing

Evaluated desalting compositions based on ion exchangers fulfil many conservation requirements: they are outstandingly easy in preparation, show good adhesion to both wet and dry stone. Hence they may be applied in even layer on widely inclined surfaces, and moreover, they are readily and easily removable leaving no staining effects.

Conducted testing proved that ion exchange in case of mixed ion exchangers takes place in weakly acidic environment (pH 6.6). Yet around their grains there appear suitable environments. Acidic once are formed around cation exchanger leading to pointlike decomposition of calcium carbonate in the contacting spot of stone with the ion exchanger grain. Filler addition - cellulose dust does not hinder this process. Use of intermediate layer of cellucotton (3 or 5 layers) protects stone from destructive cation exchanger reaction.

Desalting effectiveness of 'Piricz6w' limestone by ion exchanger based compresses is equally outstanding and comparable to cellulose dust based compositions. It is, however, much higher than at

limestone desalting with 10 layers of cellucotton. It has been also ascertained that desalting effectiveness is related to salt concentration in stone and it decreases with its increase.

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DE

Phot.l Desalting Compresses After Drying A.cellulose dust mixed with water lOOg in ldm3

B.cellulose dust: ion exchangers in volumetic ratio 1:1 mixed with water C.cellulose dust : ion exchangers in volumetic ratio 2:1 mixed with water

D.cellulose dust : ion exchangers in volumetic ratio 1:2 mixed with 0.25% methylcellulose solution E.cellulose dust: ion exchangers in volumetic ratio 1:2 mixed with 0.5% methylcellulose solution

F.cellulose dust : ion exchangers in volumetic ratio 1:1 mixed with 0.25% methylcellulose solution G .cellulose dust : ion exchangers in volumetic ratio 1 :1 mixed with 0.5% methylcellulose solucion

Phot2 Desalting Compresses After Drying H. colloidal silica: ion exchangers in volumetic ratio 1:2 mixed with 0.25% methylcellulose solution I. colloidal silica : ion exchangers in volumetic ratio 1:2 mixed with 0.5% methylcellulose solution

J. colloidal silica : ion exchangers in volumetic ratio 1 :I mixed with 0.25% methylcellulose solution K.colloidal silica : ion exchangers in volumetic ratio 1:1 mixed with 0.5% methylcellulose solution

L. talc: ion exchangers in volumetic ratio 1:2 mixed with 0.25% methylcellulose solucion M.talc: ion exchangers in volumetic ratio 1:2 mixed with 0.5% methylcellulose solution N.talc: ion exchangers in volumetic ratio 1:1 mixed with 0.25% methylcellulose solution O.talc : ion exchangers in volumetic ratio l:l mixed with 0.5% methylcellulose solution

P. anion exchangers: cation exchangers in volumetic ratio 3:1 mixed with 0.5% methylcellulose solution

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Phot.3 Colour Changes on Pincz6w Limestone Surface After Removal of Desalting Compresses

I. control stone 2. cellulose dust: ion exchangers in volumetic ratio 1:1 mixed with water

3. cellulose dust: ion exchangers in volumetic ratio 1 :I mixed with 0.5% methylcellulose solution -s light yellowing and cellulose fibres sruck to scone surface

4. colloidal silica: ion exchangers in volumetic ratio 1:1 mixed with 0.5% methylcellulose solurion -yellowing

5. talc: ion exchangers in volume tic ratio I :I mixed with 0.5% methylcellulose solution -intensive whitening

6. anion exchangers: kation exchangers in volumctic ratio 3:1 mixed with 0.5% methylcellulosc solution - intensive yellowing

Phot.4 State of 0ybnik Touchstone After Removal of Desalting Compresses I. anion exchanger Wofatit SBW - slight pointlike dulling 2. cation exchanger Wofatit KPS - sharp pointlike pittings

3. cellulose dust - strong irregular dulling 4. cellucotcon - slight dulling

5. compress I - irregular dulling, sharp pittings 6. compress II - irregular dulling, sharp pittings

7 - compress I _with three cellucon on layers - irregular dulling 8. comrrcss I wnh five cellucotton layers - irregular slight dulling

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Phot.5 State of Slawniowicki Marble After Removal of Desalting Compresses 1. compress I with three cellucotton layers - irregular slight dulling

2. compress I - slight irregular dulling, pittings 3. cellulose dust - strong dulling

4. celluconon - no changes 5. anion exchanger Wofatit SBW - no changes

6. cation exchanger Wofatit KPS - sharp pointlike pittings

Phot.6 State of Slawniowicki Marble Surface J. destilled water - slight dulling

2. cation exchanger Wofatit KPS - rough surface 3. anion exchanger Wofatit SBW - slight pointlike dulling

4. anion exchanger: cation exchanger 3:1 - dulling