effects of bulking paraloid b-72 for marble fills

Maney Publishing

EFFECTS OF BULKING PARALOID B-72 FOR MARBLE FILLSAuthor(s): JULIE WOLFESource: Journal of the American Institute for Conservation, Vol. 48, No. 2 (Summer 2009),pp. 121-140Published by: Maney Publishing on behalf of The American Institute for Conservation of Historic &Artistic WorksStable URL: http://www.jstor.org/stable/27784659 .

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EFFECTS OF BULKING PARALOID B-72 FOR MARBLE FILLS

JULIE WOLFE

ABSTRACT?To compare the effects of products used to bulk Paraloid B-72 on its properties when

used for loss compensation on white, indoor mar

ble, twenty-one fillers (including carbonates, silicates,

and sulfates, and other compounds) were studied,

along with three marble types (alabaster, Thassos,

Carrara). Color, gloss, reflectance, and hardness were

measured. Observations regarding the range of allow

able concentrations, shrinkage, capability, slump, and

general working properties are reported. Compari son of these properties is useful to the conservator

in choosing the most appropriate filler for a specific

application.

TITPJE?L'influence des materiaux de remplissage sur le Paraloid B-72 utilise comme comblement des

lacunes du marbre PRESUME?Para comparar los

efectos en las propiedades del Paraloid B-72 de varios

aditivos que se utilizan para aumentar el volumen al

hacer compensaciones en perdidas de marmol bianco, se estudiaron 21 productos (incluyendo carbonatos,

silicatos, sulfatos) y tres tipos de marmol (alabas

tro, Thassos y Carrara). Se midieron las propiedades de color, brillo, reflejo y dureza. Se incluyeron otras observaciones referentes al rango de concentra

ciones permisibles, encogimiento, habilidad de de

jarse tallar, hundimiento y propiedades generales. Los resultados obtenidos permiten hacer una com

paracion de los diferentes productos, lo cual fa

cilita escoger el mas apropiado para una aplicacion

especifica.

TITULO?Los efectos del engrosamiento de Par

aloid B-72 para hacer compensaciones en marmol

LvESUMEN?Para compara os efeitos das pro

priedades do Paraloid B-72 de varios aditivos que se utilizam para aumentar o volume no preenchi

mento de marmore branco, foram estudados vinte

e um materials, (incluindo carbonatos, silicatos,

sulfatos) jutamente com tres tipos de marmores (ala

bastro, Thassos, Carrara). Mediram-se as propriedades da cor, do brilho, da reflexao e da resistencia. Foram

acrescentadas outras observacoes, referentes ao es

copo das concentracoes permitidas, retracao, possibili dade de entalhamento, fundicao e propriedades gerais. Os resultados obtidos possibilitam a comparacao dos varios materials, o que pode ajudar na sua

escolha do mais apropriado para uma aplicacao

especifica.

TITULO?Efeitos do consolidante Paraloid B-72

no preenchimento de marmore RESUMO?Afin

de comparer les effets que divers materiaux de

remplissage ont sur les proprietes du Paraloid B-72,

lorsqu'utilise sur du marbre blanc garde dans un

environnement interieur, vingt-et-un materiaux de

remplissage (incluant des carbonates, des silicates,

des sulfates et d'autres materiaux) furent etudies

en relation avec trois types de marbres (albatre, de Thassos et de Carrare). La couleur, l'eclat, le

reflet et la durete de ces materiaux ont ete evalues.

Des observations sont faites sur les concentrations

souhaitables, le retrecissement, la possibilite de travail

mecanique, l'affaissement, ainsi que les proprietes

generates de travail. Une comparaison de ces pro

prietes permet au conservateur de choisir le materiau

de remplissage le plus adequat pour une application

specifique.

1. INTRODUCTION

White, calcareous marbles are often composed of

dolomite and calcite with a wide variety of min

erals that can affect color, texture, and hardness.

Each piece of marble has a characteristic appear ance and translucency, influenced by various crys tal morphologies (Solomon and Hawthorne 1983). Even within a single marble sculpture, there are sub

tle variances. Thus, no single formulation can suf

fice for filling losses. Moreover, when making a fill

that mimics the appearance of marble, the facade or

appearance is not the only property to be consid

ered. Adapting a list from Griswold and Uricheck

(1998), the fill material should also be workable,

easy to carve, stable, reversible, nonshrinking, free

from air bubbles, and variable in hardness, color, and

translucency.

Trying to match a bulked resin to a marble is

complex because their optical properties are so inher

ently different. They reflect, transmit, refract, disperse, and polarize light to varying degrees, making the

analysis of these properties extremely complex. A fill

that is too opaque, for example, can appear dark and

JAIC 48 (2009):121-140



122

JULIE WOLFE

Fig. 1. The lost outside rim of the carved marble ear was filled using Paraloid B-72 bulked with crushed alabaster powder, backlit to show the translucency of the fill.

visually distracting. Ideally, the fill will have the same

response to light as the adjacent marble. An exam

ple of a matching fill on a marble sculpture can

be seen in figure 1. While a completed fill can al

ways be modified in color, gloss, and reflectance us

ing techniques such as coating or inpainting, using a

fill material with optical properties matching those of

marble can eliminate the need for additional treatment

steps. Previous studies have focused on a limited num

ber of fillers, resins, or one mixture (Gansicke and

Hirx 1997; Griswold and Uricheck 1998; Nagy 1998; Larkin and Makidrou 1999). In practice, it is common

to add different fillers into one resin to customize the

fill material for a particular treatment. Speaking to

the need for great variability, this paper attempts to

quantify and classify the range of working and phys ical properties produced when individual fillers are

combined with a single synthetic resin. With greater

knowledge of the properties of bulked resins, it may be

possible to better control the fill and eliminate addi

tional treatment steps such as inpainting or coating to

adjust the final color, gloss, and translucency. The goal of the study is not to prescribe a fill recipe or applica tion method, but rather to provide useful comparative data to aid the conservator in choosing between the

different options. For example, comparing hardness

between fillers can be useful if one needs to minimize

carving, filing, and sanding.

Comparing the effects of bulking a resin with

fillers is a complicated study. As explained by Plued

demann and Stark, "The interface between polymer

JAIC 48 (2009):121-140



123


and filler involves a complex interplay of physical and

chemical factors related to composite performance"

(1977, 1). Filler properties such as particle shape, par ticle size, and refractive index modify the composite in

hardness, translucency, color, slump, and more. Keep

ing in mind the interfacial relationship between the

filler and polymer, the effects of solvent type and spe cific properties of the filler allow for an unlimited

number of variables. For that reason, the most useful

approach to understanding how fillers affect Paraloid

B-72 and the only way to tackle a project of such

complexity was to start by looking at them in a simple manner that would eliminate as many variables as pos sible. Rather than looking at a set of known recipes

currently used in practice, this study takes a step back

in order to expand the options and reduce the vari

ables by isolating one filler type, in one resin system, and one solvent.

2. PREPARATION OF COUPONS

2.1 FILLERS

Drawing from publications, personal communi

cations with colleagues, and product research, twenty one different filler types were chosen that are in com

mon use in conservation and that could be used

to compensate for losses on white marble. Twenty five different formulations were prepared for testing

(table 1). The formulations have been given coupon numbers and are organized according to their clas

sification as carbonates, silicates, sulfates, or other

compounds. A range of marble powders include manufactured

products as well as hand-ground alabaster and mar

ble. Larson (1978) describes crushed and boiled al

abaster for marble filling, which is commonly used,

and recommends heat treatment of alabaster to in

crease whiteness; heat treatment has been noted to

change hardness and translucency (Pullen 2004). Al

abaster for this study was purchased from a local marble

supplier. Boiled samples were prepared by immersion

in water at 97?C for three hours. Compared to un

boiled alabaster, the boiled samples showed greater

opacity and were notably softer to crush with the

IKA Labortechnik MF10 basic grinder (fig. 2). The

other sulfate fillers include alabaster plaster (calcium sulfate hemihydrate), terra alba (calcium sulfate dihy

drate), and blanc fixe (purified barium sulfate with

controlled particle size by precipitation).

A white calcium and magnesium carbonate mar

ble from Thassos was purchased from a local sup

plier for hand grinding, using an IKA Labortech

nik MF10 basic grinder, set at 3000 rpm/min. To

look at the effects of particle size within one filler

type, the hand-crushed Thassos was sifted to create

five different groups having particle sizes 0?0.6 mm,

0.425-0.6 mm, 0.3-0.425 mm, 0.15-0.3 mm, and

0.075-0.15 mm. Studies made by Malaga-Starzec et

al. indicate that "intergranular decohesion begins at

temperatures between 40? and 50?C (104-122?F) for some marble types" due to thermal expansion and contractions, calcite more than dolomite (2003,

306). The Thassos marble was baked in a Ther

molyne Furnace 1400 for 12 hrs at 600?C (1112?F) to force microfracturing between the grains, then

crushed, and sieved to 0?0.6 mm. The marble did

appear brighter, more opaque, and was easier to

crush after baking. Some yellowing was also visually observed.

Marble dust-M, a commercially available ground natural calcium carbonate from Kremer Pigments, was

included. Calcite, which is formed by the crystal lization of calcium carbonate below 30? C (Solomon and Hawthorne 1983), was also purchased from

Kremer.

Other carbonates were chosen from Specialty

Minerals, manufacturer of natural marbles to varying

particle size and shape, brightness, and density. Their

products are high in purity through controlled pro

cessing. The ATF 40 comes from a product line that

is made from limestone and is used commercially for

tile/sheet flooring, roofing, and other building prod ucts. The Vicron 45-3 is also natural limestone, high in

calcium. Marblewhite 200 comes from calcite ore and

is made for greater brightness. ViCALity Ultra Heavy PCC is a calcitic, precipitated calcium carbonate. The

four different Specialty Mineral products were chosen

to represent a range of compositions and particle sizes

and shapes. Another precipitated calcium carbonate from

Conservation Support Systems was added for com

parison. Precipitated calcium carbonates have been

used industrially in resins for greater brightness, smaller particles size, greater purity, and higher gloss than natural calcium carbonate (Gachter and Muller

1985). Fumed silica is difficult to use in acetone; Evonik

Degussa (Vail 2005) recommended using a hydropho bic product, Aerosil R 7200, that is treated with a

methacryloxy functional silane (2-Propenoic acid,

JAIC 48 (2009): 121-140



124

JULIE WOLFE

Table 1. List of coupons with filler information as supplied by the manufacturer (product, composition,

supplier) and formulation. The formulation is given as grams (milliliters) of filler in 30 ml of 60% w/v Paraloid

B-72 (18 g B-72 in 30 ml acetone). Properties of the fills based on visual observations are listed.

Coupon Filler information

Formulation

g(ml) Visual observations on the fills

ATF 40 48 (27.5) 96% CaC03) 1% MgC03, <0.2%H2O Particle size: 0.07?0.15 mm; par ticle shape: random, crushed

Specialty Minerals

Calcite 41 (35) CaC03 Kremer Pigments (58720)

Marble dust-M, very fine 54 (45) Natural CaC03 Particle size: 0-0.6 mm

Kremer Pigments (59600)

Marblewhite 200 42 (40) 96% CaC03, 1% MgC03, <0.1%Fe2O3, <0.1%H2O Particle size: 0.045-0.074 mm

Specialty Minerals

Precipitated calcium carbonate 15 (35) CaC03 Particle size: around 0.04 mm

Conservation Support Systems

Thassos marble 74 (40) CaC03 and CaMg(C03)2 Particle size: <0.6 mm

Carnevale & Lohr

Thassos marble 67 (40) CaC03 and CaMg(C03)2 Particle size: 0.425-0.6 mm

Carnevale & Lohr


Carnevale & Lohr


Carnevale & Lohr

Wet putty has a gritty texture, yellowish, mottled

surface coloration, has small black inclusions, low

polish obtainable (uneven), hard to carve with

scalpel, hard to file with diamond file, fair to sand

with 1500 Micro-mesh, medium amount of air

bubbles, has a crystalline sparkle. Wet putty has a gummy texture, even coloration,

high polish obtainable, hard to carve with scalpel (brittle), hard to file with diamond file, fair to sand

with 1500 Micro-mesh, numerous air bubbles.

Wet putty has a gummy texture, slightly mottled

coloration, high polish obtainable, hard to carve

with scalpel (brittle), fair to carve with diamond

file, fairly hard to sand with 1500 Micro-mesh, numerous air bubbles.

Wet putty has a gummy texture, even coloration,

high polish obtainable, hard to carve with scalpel, hard to file with diamond file, hard to sand 1500

Micro-mesh, numerous air bubbles (hard to fill

them). Wet putty has a gummy texture, even coloration,

high polish obtainable, hard to carve with scalpel (brittle), hard to file with diamond file, slightly hard to sand with 1500 Micro-mesh, numerous

air bubbles, coupon dried with wrinkled surface. Wet putty has a gritty texture, slightly mottled

coloration, low polish obtainable (uneven), hard to carve with scalpel (brittle), fair to carve with

diamond file, hard to sand with 1500 Micro

mesh, numerous air bubbles, small-large crys talline sparkle.

Wet putty has a gritty texture, slightly mottled



mesh, numerous air bubbles, slight small crys talline sparkle.


coloration, low polish obtainable (uneven), hard to carve with scalpel (brittle), fair to carve with diamond file, hard to sand with 1500 Micro






(Continued on next page)

JAIC 48 (2009):121-140




125

Table 1. (Continued).


Formulation

g(ml) Visual observations on the fills

10

11

12

13

14

15

16

17

18

Thassos marble 45 (37.5) CaCOjand CaMg(C03)2 Particle size: 0.075-0.150 mm

Carnevale & Lohr

Thassos marble?baked 26 (25) CaCOj and CaMg(C03)2 Carnevale & Lohr

Particle size <0.6 mm

ViCALityUltra Heavy PCC 55 (37.5) 60-100% CaC03 <0.2% H20 Particle size: <0.6 mm

Specialty Minerals

Vicron 45-3 48 (47.5) 97% CaC03} 0.5% MgC03, <0.1%>Fe2O3} <0.2% water

Particle size: 0.010 mm

Specialty Minerals

Aerosil R 7200 15 (62.5) Si02 Particle size: 12 nm avg. Evonik Degussa

Cristobalite, very fine 23 (32.5) Si02 Particle size: 0.008 mm

Kremer Pigments (58689) Glass flakes 40 (50) SiOz Kremer Pigments (ZK59852)

K15 Scotchlite glass bubbles 3 (42.5) 97-100%) soda lime borosilicate

glass, 3%o Si02, amorphous Particle size: 0.030-0.105 mm

3M

Talc: Nicron 400 powder 28 (35)

MgO-4SiO2-H20 TAP Plastics





Baked, crushed, and sieved. Wet putty has a gritty texture, even coloration, low polish obtainable, hard to carve with scalpel, hard to carve with di

amond file, hard to sand with 1500 Micro-mesh, numerous air bubbles, small crystalline sparkle.

Wet putty has a gummy texture, slightly mottled

coloration, high polish obtainable, medium-hard to carve with scalpel, fair to file with diamond

file, fairly hard to sand with 1500 Micro-mesh,

very few air bubbles.


high polish obtainable, hard to carve with scalpel

(brittle), fairly hard to carve with diamond file, fair to sand with 1500 Micro-mesh, numerous air

bubbles (large), dry coupon cracked at center.

A two step process was used resulting in a mixture

of 15 g R 7200 and 36 g B-72. Wet putty has a stiff/taffy texture, slightly mottled coloration,

high polish obtainable, hard to carve with scalpel, hard to carve with diamond file, hard to sand with

1500 Micro-mesh, numerous air bubbles.


high polish obtainable, hard to carve with scalpel, hard to carve with diamond file, hard to sand with

1500 Micro-mesh, numerous air bubbles.

Wet putty has a gummy texture, slightly mot

tled coloration, medium polish obtainable, soft

medium to carve with scalpel, medium to carve

with diamond file, medium to sand with 1500

Micro-mesh, numerous air bubbles, small crys talline sparkle.

Wet putty has a spongy texture, even coloration, low polish obtainable, very soft to carve with

scalpel, very soft to carve with diamond file, soft to sand with 1500 Micro-mesh (too soft, pores

trap grit), numerous air bubbles.

Wet putty has a gummy/stiff texture, mottled col

oration, low polish obtainable, soft to carve with

scalpel, soft to file with diamond file, fair to sand

with 1500 Micro-mesh, numerous air bubbles

(hard to fill them).

(Continued on next page)

JAIC 48 (2009): 121-140



126

JULIE WOLFE

Table 1. (Continued)


Formulation

gM) Visual observations on the fills

19 Alabaster plaster 27 (32.5)

CaSOr0.5H2O Kremer Pigments (58340)

20 Alabaster, ground 43 (42.5) CaS04 Particle size: <0.6 mm

Carnevale & Lohr

21 Alabaster, boiled 43 (42.5) CaS04 Particle size: <0.6 mm

Carnevale & Lohr

22 Blanc fixe 38 (32.5) BaS04 Particle size: <0.8 mm


23 Terra alba 25 (32.5) CaSOr2H20 Particle size: 0.001-0.07 mm


24 Polywax 2000 20 (32.5) -[CH2-CH2]-n Conservation Support Systems

25 Whatman ashless cellulose 6 (22.5) powder

Thomas Scientific

Wet putty has a gummy texture, mottled col

oration, high polish obtainable, medium to carve

with scalpel, hard to file with diamond file, fair

to sand with 1500 Micro-mesh, fair amount of

air bubbles (hard to fill them), dry coupon had numerous cracks.

Wet putty has a gritty texture, even coloration, medium polish obtainable, soft to carve with

scalpel, soft to carve with diamond file, fair to sand

with 1500 Micro-mesh, numerous very small air

bubbles, small crystalline sparkle. Wet putty has a gritty texture, even coloration, medium polish obtainable, soft to carve with

scalpel, soft to carve with diamond file, fair to

sand with 1500 Micro-mesh, numerous air bub

bles, small crystalline sparkle. Wet putty has a gummy texture, even coloration,

high polish obtainable, medium to carve with

scalpel, medium to carve with diamond file, fair to


bles (hard to fill them), coupon dried with wrin

kled surface.

Wet putty has a gummy texture, slight mot

tled coloration, medium polish obtainable, soft

medium to carve with scalpel, medium to file

with diamond file, medium to sand with 1500

Micro-mesh, numerous air bubbles (hard to fill

them), dry coupon had numerous cracks.


coloration, medium polish obtainable (uneven), soft to carve with scalpel, soft to carve with

diamond file, medium-hard to sand with 1500

Micro-mesh, numerous air bubbles forms a crys talline like surface.

Wet putty has a spongy texture, even coloration, medium polish obtainable, hard to carve (brittle), medium to carve with diamond file, medium to


bles.

2-methyl-, 3-[trimethoxysilyl]propylester). This

product should allow for higher loading levels and

better miscibility in acetone systems. Also included

within the class of silicates are cristobalite, a form

of silica that occurs at high temperatures, and glass

flakes, processed from amorphous silicon, aluminum,

calcium, boron, and magnesium oxides, both from

Kremer. From the range of glass microballoons

available, a common, low-cost product of hollow

glass spheres called K15 was chosen from 3M. Talc

(hydrated magnesium silicate) is commonly used for

bulking; a Nicron 400 powder was chosen as an

asbestos-free product. A Whatman ashless cellulose powder (long chain

molecules of cellulose) has been commonly used to

give a softer fill and improve carving properties. Wax

can give a nice translucency to a fill; a Polywax 2000

(ethene homopolymer, melting point 126?C/259?F)

JAIC 48 (2009):121-140



127


^nraU^L^k-B^ i_i^HHL_i^L_HL_L_H__i_L__^ ^^HHHHH

_i_i_H_^9i_i_HtM_i_i_i^i_B^ - .^-^^^H^^r^ ?H

j^^^^^Mr ^ ̂ ̂

^^^^^^^ JhH

Fig. 2. Two pieces from the same sheet of alabaster. Left: untreated, later crushed for use in coupon no. 20. Right: boiled, later crushed for use in coupon no. 21.

was chosen and ground into a powder using a Krupps coffee grinder.

2.2 RESIN MIXTURE

Paraloid B-72 and acetone were chosen as the

resin-solvent mixture. Paraloid B-72 was selected

since the resin is commonly used for marble loss com

pensation and it is an accepted, conservation-grade material having long-term stability. Acetone is a good solvent for Paraloid B-72 (Hansen 1995; it is fast evap

orating, and allows for a quick-setting fill. In order to

choose a concentration, a small study was carried out

to compare the effect of filler concentration on bulk

ing properties of four different resin mixtures (20%,

40%, 50%, and 60% w/v). Each filler was added to

each of the four resin mixtures by adding 1.2 ml in

crements of filler to 30 ml of resin in acetone, taking a

small sample after each addition. The test mixture was

first sampled when the resin became opaque; sampling was terminated when the mixture became too stiff to

work more filler into the resin. Occasionally, the dried

fill broke apart or cracked when dry; this was noted as

a filler concentration threshold limit. From this study, it was found that the quantity of filler added to Par

aloid B-72 is more variable at a resin concentration

of 60% w/v; therefore, a final resin concentration of

60% w/v was chosen to prepare coupons for testing.

2.3 FILLER CONCENTRATION

As Larkin and Makidrou (1999) have found, each

type of filler will require very different filler-resin ra

tios to give comparable results. It was confirmed dur

ing the resin concentration study that each filler had

varying capacities to bulk Paraloid B-72. For exam

ple, it was observed that Thassos (>0.6 mm) could be

added up to approximately 400% of the weight of the

resin, whereas, the K15 could only be added to 17%

of the weight. In the resin concentration study, the

maximum filler concentration in a 60% w/v Paraloid

B-72 solution, or the concentration threshold limit, was determined for each filler. The concentration of

each filler used to prepare coupons was one milliliter

below its concentration threshold limit. The amount

used in each of these formulations is given in table 1.

2.4 MAKING THE TEST COUPONS

The filler was mixed into 30 ml of 60% w/v Paraloid B-72 in acetone (18 g B-72 in 30 ml ace

tone) into a putty consistency and cast into three

JAIC 48 (2009):121-140



128

JULIE WOLFE

polycarbonate cups lightly coated with Vaseline as

a release agent. To minimize the inadvertent intro

duction of variables, all sample preparation was exe

cuted by a single person following a structured routine.

Many of the cast fills formed air bubbles at the surface

of the mold, and for the purpose of optical testing, the

bubbles were filled on one of the three coupons us

ing the same formulation applied with a microspatula. The coupons with filled air bubbles were sanded on

a rotating sanding wheel to 12,000 grit using Buehler

sanding paper and Micro-mesh, a cushioned abrasive

cloth. The natural marbles used in the testing set were

core-drilled and polished by a local marble supplier. The faces of the highly polished testing coupons were

taped across one half and sandblasted to show the com

parison between high polish and a matte surface. The

final set of twenty-five coupons with the three marble

types are shown in figure 3. The other two sets of

coupons were also polished and were used for visual

observations, carvability testing, and Vickers hardness

testing. The Aerosil R 7200 required a slightly different

preparation method from the rest of the fillers. An

additional step was required to obtain a fill that formed

a coherent composite. The fill would initially appear coherent when wet, but frequently crumbled after

drying. Mixing techniques such as varying the speed of adding the silica and prewetting the filler in acetone

were tried without effect. Finally, a crumbled sample made from 62.5 ml (15 g) Aerosil R 7200 in 30 ml Paraloid B-72 was ground in a coffee grinder to make

a modified filler that comprised both the resin and

the R 7200. This ground up powder was then added

to 30 ml 60% w/v Paraloid B-72 which resulted in a

stronger composite that did not break apart (fig. 4).

Therefore, the coupon formulation is composed of

15 g Aerosil R 7200 and 36 g Paraloid B-72 (table 1). The results indicate that it is possible to avoid a weak,

crumbling fill by using a two-step process: bulking the

Paraloid B-72 as much as possible while wet, letting it

dry, and grinding the resulting fill to use as the filler

in the final step of preparation.

3. PROPERTIES OF THE TEST COUPONS

3.1 VISUAL OBSERVATIONS

During the process of testing for optimal resin

concentrations, the working properties of the wet fill

mixtures were described as gritty, spongy, gummy, or

stiff. The consistency has been described as "gritty" if

it felt like wet sand, "spongy" if it felt airy and light,

"gummy" if it felt sticky, and "stiff" if it was dense

and hard to compress.

3.1.1 Shrinkage

Shrinkage could cause failure in the fill, or might necessitate several thin applications to build up the fill

during treatment. Since the casting molds have a con

sistent diameter of 2 cm, shrinkage could be evaluated

by measuring the coupons after one month of drying.

Shrinkage was not an obvious problem within the set

of coupons, with the exception of Aerosil R 7200,

which showed the greatest change. A small amount of

shrinkage was noticed in the coupons containing talc,

calcite, Marbledust-M, and all of the sulfates.

3.1.2 Cracking and Wrinkling

Cracking of the dried fill can indicate a poor rela

tionship within the resin-filler-solvent system. Crack

ing was found to be more common with the sul

fate class, in particular alabaster plaster, and terra alba.

Within the carbonate class, Vicron 45-3 dried with

a single crack across the middle. The coupons com

posed of blanc fixe and precipitated calcium carbonate

dried with a wrinkled surface where the fill was ex

posed to air. It is suggested that the phenomenon of

wrinkling is caused by the surface of the fill drying more quickly than the body of the fill.

3.1.3 Homogeneity

A difference in homogeneity was noticed, as some

of the putties dried with a mottled surface coloring,

indicating an uneven distribution of the filler particles within the matrix. Mottled surfaces included the ATF

40, Marble dust-M, all of the Thassos formulations

except the baked, ViCALity Ultra Heavy, Aerosil R

7200, glass flakes, talc, alabaster plaster, terra alba, and

Polywax 2000. As various marble types could also have

a mottled surface coloration, this property could be

used intentionally if desired. However, if the goal is

to imitate a marble with even surface coloration, it is

best to avoid these fillers.

JAIC 48 (2009): 121-140




129

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JULIE WOLFE

Fig. 4. Two coupons of Paraloid B-72 bulked with Aerosil R 7200. Left: coupon A, 12.5 teaspoons of R 7200 in 30 ml

Paraloid B-72 solution, crumbled after drying. Right: coupon B was made by crushing coupon A and using it as a filler to

make a more coherent fill.

3.1.4 Bubbles

The formation of bubbles was a problem with

nearly all of the fillers. Fast evaporation of the solvent

at the surface of the putty has the potential to trap air bubbles. The three fillers showing the fewest bub

bles respectively include the ViCALity Ultra Heavy, Vicron 45-3, and glass flakes. When comparing the

different coupons with Thassos, the smaller particle size (0.175-0.150 mm) showed the least amount of

bubbles. There appeared to be fewer air bubbles with

the unboiled alabaster powder than with the boiled

alabaster.

3.1.5 Sanding

During the preparation of the coupon set, it was

noted that the K15 and cellulose powder were diffi

cult to sand due to their softness. Both were prone to

collecting grit from the sanding process, which tended

to darken the surface unevenly. In general, all of the

coupons were easily discolored by colored sandpa

pers except for precipitated calcium carbonate, talc,

and terra alba. To avoid this problem, each coupon was sanded using 1500 grit yellow Micro-mesh. The

hardest were observed to be Marble dust-M, Marble

white 200, precipitated calcium carbonate, Thassos

(all formulations), and Polywax 2000.

3.1.6 Slump

The slump was measured by adapting a draw

down technique developed by the paint industry. A

group of 30 ml plastic syringes were drilled out at the

needle attachment to enlarge the orifice to a diameter

of 5/16 in. Each formulation was loaded into a clean

syringe, and fill material was extruded onto a piece of

Mylar. A scalpel was used to cleanly cut the fill mate

rial from the syringe to produce a rod of fill material

3/4 in. x 5/16 in. diameter. The piece of Mylar was

attached with double-sided tape to a vertical board, to

allow for measurement of the effect of gravity on each

of the cast rods of fill material (fig.5). The distance that

the fill material slumped was measured from its origi nal horizontal position along the vertical center of the

rod. In general, the carbonate fillers showed the great est slump. The Aerosil R 7200 and the alabaster fillers

showed the least amount of slump. Based on this test,

the fillers have been ranked from most to least slump in table 2.

3.1.7 Carving and Filing

Having a fill that is softer than the marble being

repaired is desirable to avoid abrading the stone ad

jacent to fills during finishing by carving or filing. A

Heson D126 diamond needle file was tested on each

of the coupons and results described each material as

hard, fair, or soft (table 1). Each coupon was also hand-carved using a #15

carbon steel surgical blade, and generally ranked from

hard to soft (table 2). The fills that were quite difficult to carve included all of the Thassos formulations, ATF

40, calcite, Marbledust-M, precipitated calcium car

bonate, and cristobalite. When comparing the differ

ent Thassos formulations, it was observed that higher

particle size made the fill harder to carve with a scalpel. It was interesting to note that the results obtained us

ing a scalpel did not always correlate to results using a diamond file. For example, it was easier to carve

down the Thassos coupons using the diamond file

rather than a scalpel.

JAIC 48 (2009):121-140



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mm m

Fig. 5. Slump testing of the 25 bulked Paraloid B-72 fill formulations

JAIC 48 (2009):121-140



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JULIE WOLFE

Table 2. Fillers and marble ranked by properties from visual observations. From top to bottom, slump is ranked

from low to high. The ability to be carved with a scalpel is ranked from soft to hard. The translucency is ranked

from opaque to translucent based on transmittance of a fiber optic light source. Coupon numbers are listed in

brackets. Pure marbles are in bold.

Slump

LOW SLUMP Aerosil R 7200 [14] Alabaster ground [20] Alabaster boiled [21] Alabaster plaster [19] Cellulose powder [25] Cristobalite [15] Blanc fixe [22] Terra alba [23] ATF 40 [1] K15 glass bubbles [17] Talc Nicron 400 [18] Polywax 2000 [24] Thassos (<0.6 mm) [6] Ppt. calcium carbonate [5] Glass flakes [16] ViCALity Ultra Heavy [12] Baked Thassos (<0.6 mm) [11] Thassos (0.15-0.3 mm) [9] Thassos (0.075-0.15 mm) [10] VICRON 45-3 [13] Thassos (0.425-0.6 mm) [7] Calcite [2] Thassos (0.3-0.425 mm) [8] Marbledust-M, very fine [3] Marblewhite 200 [4] HIGH SLUMP

Carvability (scalpel) SOFT K15 glass bubbles [17] Alabaster ground [20] Alabaster boiled [21] Talc Nicron 400 [18] Alabaster plaster [19]

Polywax 2000 [24] VICRON 45-3 [13] Terra alba [23]

ViCALity Ultra Heavy [12] Cellulose powder [25] Glass flakes [16] Marblewhite 200 [4] Blanc fixe [22] * AerosilR7200 [14] Calcite [2] Ppt. calcium carbonate [5] Cristobalite [15] Marbledust-M, very fine [3] Thassos (0.3-0.425 mm) [8] Thassos (<0.6 mm) [6] Thassos (0.15-0.3 mm) [9] Thassos (0.075-0.15 mm) [10] Thassos (0.425-0.6 mm) [7] ATF 40 [1] Baked Thassos (<0.6 mm) [11] HARD

Translucency (fiber optic)

OPAQUE Alabaster plaster [19]

Ppt. calcium carbonate [5] Calcite [2] VICALity Ultra Heavy [12] Marblewhite 200 [4] VICRON 45-3 [13] Talc Nicron 400 [18] Terra alba [23] Blanc fixe [22] Thassos (0.075-0.15 mm) [10] Baked Thassos [11] Marbledust-M [3] Glass flakes [16] Thassos (0.15-0.3 mm) [9] ATF 40 [1] Thassos (<0.6 mm) [6] Thassos (0.3-0.425 mm) [8] Thassos (0.425-0.6 mm) [7] K15 glass bubbles [17] Alabaster ground [20] Alabaster boiled [21] Cristobalite [15] Polywax 2000 [24] Cellulose powder [25] Pure Thassos

Aerosil R 7200 [14] Pure Carrara

Pure Alabaster

TRANSLUCENT

3.1.8 Translucency

Creating a fill that mimics the translucency of

marble is the greatest challenge. Light reflected from

a marble surface affects its brightness, and light ab

sorbed into marble scatters to create a glow that can

be difficult to measure with accuracy and recreate.

A simple technique using a fiber optic light source

was used to compare the translucent properties of the

coupons. Placing a fiber optic light source on the side

of a coupon adjacent to the top face allowed for a

general measurement of the depth of light penetra tion within the sample (fig. 6). A Vernier caliper was

used to measure the light penetration in centimeters.

The coupons were ranked from opaque to translu

cent in table 2 based on the measurement of light

penetration; the actual measurements are reported in

table 3.

In general, the coupon set showed a great range of

translucency. Though the results are difficult to cor

relate with actual marble, it is clear that many of the

coupons are either too opaque or translucent. A gen eral observation can be made that the more translucent

coupons tend to have a gray cast, which may or may not be desired. The particle size of a filler can affect the

translucency of a composite, and it was possible to ob

serve this trend when comparing the different Thas

sos formulations. Opacity increased with a decrease in

particle size of the Thassos. The baked Thassos when

used as a filler made the fill less translucent. In con

trast, the treatment of the alabaster by boiling made

the fill more translucent.

JAIC 48 (2009):121-140



133


t s 111?*lj I

* * *|J

* *1 * I * *21

* *'11

* *3 j1''1J1 *J|

j *111 j1

Fig. 6. Using a fiber optic light source to measure light trans

mittance on coupon no. 1, bulked with ATF 40

3.2 INSTRUMENTAL TESTING

3.2.1 Hardness

To compare differences in hardness, a Vickers

Hardness Testing Instrument, (40 x oculus, 25-500

gram force, obtained from Buehler Ltd.), was used

on the coupons to obtain measurements in Vickers

(HV). It would be unusual to know the actual HV

of a marble being treated; however, the comparison of HV found on actual marble with the test coupons can give numerical data describing the sample's ability to resist plastic deformation. Vickers measures hard

ness using a penetration technique, and results may not necessarily correlate with other hardness proper ties such as bending, scratching, abrasion, or carving. In fact it was observed, albeit subjectively, that cap

ability did not directly correlate with Vickers ratings. Of the hard-to-carve fills, HV values are random, and

ranged from HV13 to HV235. All of the formulations

have a lower HV than Thassos marble, but it appears that these values cannot be directly associated with the

practical application of carving. HV values are listed in table 3; the fillers have

been ranked by average HV value from hard to soft in

table 4. Paraloid B-72 was measured at HV6-8, which

showed that most of the fillers increased the hard

ness of the resin, with the K15, Aerosil R 7200, talc,

cristobalite, blanc fixe, and precipitated calcium car

bonate being exceptions. Another observation about

the fillers with larger particle sizes and wide parti cle size distribution is that they demonstrate a greater

range of HV across the surface. Comparatively, a sam

ple of actual Thassos marble also shows a range of

hardness across the surface. The Vickers testing tech

nique is done on a micro scale, so it is not surprising that fillers having larger and more varied particle sizes

will give a range of measurements.

An interesting observation could be made about

the difference in baked and unbaked Thassos marble.

The uncrushed marble samples were compared, and

the process of baking decreased the HV of Thassos.

The decrease in hardness was not observed, however,

when the baked and unbaked samples were used as a

filler. The formulations using baked and unbaked filler

gave relative HV values. Similar results were observed

with the boiled and unboiled alabaster; the uncrushed

samples show the boiled alabaster as softer than the un

boiled. When the boiled and unboiled alabaster was

crushed and used as a filler, there were insignificant differences in hardness between them. This suggests that the heat treatments have softened the stone struc

ture, yet do not change the hardness properties when

the stone is used as a filler in Paraloid B-72. Heat treat

ing the stone prior to crushing may have the benefit

of making the material easier to crush.

3.2.2 Gloss

Gloss measurements of the coupons were taken

using a Statistical Novo-Gloss glossmeter from Mac

beth. The instrument measures in gloss units (GU) where 100 GU records all specular light, which can

be found in a perfect mirror. Low gloss units indicates

diffuse reflection as on a matte surface. The actual

gloss values are found in table 3; the fillers are ranked

from high to low gloss in table 4. The different fillers

showed a lot of variation in the coupon's ability to

produce a high polish. Figure 7 shows the coupon set photographed with a strong specular light to show

the variation in surface gloss. In general, the carbon

ates and sulfates with small particle sizes obtained the

most gloss, even higher than the polished pure Thassos

marble. In contrast, fillers with larger particle sizes and

wider particle size distributions, such as the crushed

Thassos and ATF 40, were at the lower end of the

gloss scale and could not achieve as much polish as

the pure Thassos.

3.2.3 Color

Color appearance was studied using CIE L*a*b*

to compare the relationship among the different

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JULIE WOLFE

Table 3. Properties of the polished coupons from the instrumental testing: Translucency measured in cm of

fiber optic light penetration (FO in cm), Vickers hardness (HV) given by the range of readings from low to

high, gloss units (GU at 60? reflectance angle), and CIE L*a*b* for both the polished and unpolished coupons.

polished coupons

Coupon Filler (or actual marble) FO HV GU L*

unpolished coupons

L*

1 ATF 40 1.00 13-37 36.3 65.18

2 Calcite 0.31 17-31 83.5 81.10

3 Marbledust-M 0.70 14-43 84.2 78.82

4 Marblewhite 200 0.35 13-42 81.7 84.30

5 Precipitated calcium 0.29 2-3 68.7 89.40

carbonate

6 Thassos (<0.6 mm) 1.00 17-235 23.5 67.78

7 Thassos (0.425-0.6 mm) 1.29 16-49 21.7 69.26

8 Thassos (0.3-0.425 mm) 1.20 26-176 16.0 70.55

9 Thassos (0.15-0.3 mm) 0.85 25-55 18.6 71.73

10 Thassos (0.075- 0.60 16-22 47.0 74.33

0.15 mm) 11 Thassos baked

(<0.6 mm) 12 ViCALity Ultra Heavy 0.31 9-16 73.8 91.30

13 Vicron45-3 0.35 11-15 84.1 86.95

14 AerosilR7200 2.60 1-3 67.6 44.56 15 Cristobalite 1.90 1-3 39.8 48.58

16 Glass flakes 0.71 10-17 30.8 87.52

17 Kl5 glass bubbles 1.40 2-3 8.3 92.63

18 Talc: Nicron 400 0.39 3-4 33.6 63.87

19 Alabaster plaster 0.21 9-18 76.9 75.47

20 Alabaster (<0.6 mm) 1.65 6-18 59.6 67.98

21 Alabaster boiled 1.85 9-15 48.0 68.42

(<0.6 mm) 22 Blanc fixe 0.55 3-5 92.3 86.53

23 Terra alba 0.40 13-17 47.8 55.12

24 Polywax2000 1.90 4-12 53.1 61.06

25 Whatman cellulose 2.05 311 62.2 56.14

powder Alabaster

Alabaster, boiled

Thassos marble

Thassos marble, baked

Carrara marble 2.80 56.2 54.99

Paraloid B-72 6-8

4.00 22-34 24.4 15.14

13-16

2.50 174-287 80.5 68.08

36-128

-0.43

0.07

0.24

0.56

0.07

0.15

0.24

0.28

0.41

0.42

0.39

0.27

0.25

-1.65

0.28

0.34

-1.03

2.44

0.29

0.19

-0.04

0.54

0.07

0.02

-0.79

-0.35

-0.65

3.64

1.50

2.47

3.65

2.45

-0.99

-1.30

-0.21

-0.34

-0.12

4.29

1.25

-0.12

-2.58

0.97

0.42

0.71

6.57

-0.39

-0.34

3.40

4.59

-2.20

-1.02

3.53

-1.89

-4.52

67.72

84.04

81.74

86.82

91.63

73.45

72.34

73.33

72.72

76.97

B.33 -0.22 1.77 89.23

93.33

89.72

46.87

54.60

89.89

91.04

72.24

80.64

74.97

74.02

89.59

64.68

66.57

66.47

-0.75

0.11

0.12

0.41

-0.02

0.20

0.23

0.02

0.44

0.46

-0.39

0.50

0.23

-0.12

-1.72

0.23

0.29

-1.12

2.11

0.17

0.07

0.05

0.10

0.03

0.00

4.04

0.63

2.29

2.94

2.41

-1.14

-1.00

-0.38

-0.45

-0.24

2.12

3.23

0.87

-0.20

-2.12

0.94

0.47

-1.21

9.02

-0.82

-0.85

2.70

1.74

-1.02

-1.42

coupons, whereby a* is the red-green coordinate, b*

is the yellow-blue coordinate, and L* is brightness. The results show a wide range of CIE L*a*b* values

between the test coupons indicating that the overall

coupon set gives a potentially good palette for match

ing actual marble. The sulfate fillers showed the widest

variation of b* values within a class of types. When working with white marbles, the yellow

ness or blueness of the filler is significant for color

matching; therefore, the test coupons have been sorted

by their b* values in table 4. The actual values are

listed in table 3. While these color variations can be

observed by the human eye, spectrophotometry pro vides an objective comparison. It was observed that

for most of the coupons, the polished surface became

more yellow in color. The exceptions are ATF 40,

Thassos (0.425-0.6 mm), and alabaster plaster, show

ing no change between polished and unpolished; and

baked Thassos, cristobalite, K15, and Polywax 2000,

becoming more blue when polished. The tendency

JAIC 48 (2009):121-140



135


Table 4. Fillers and marble ranked by properties from instrumental testing. Coupon numbers are listed in

brackets. Pure marbles and Paraloid B-72 are in bold.

Hardness (HV)

SOFT

Aerosil R 7200 [14] K15 glass bubbles [17]

Ppt. calcium carbonate [5] Cristobalite [15] Blanc fixe [22] TalcNicron 400 [18] Cellulose powder [25] Paraloid B-72

Polywax 2000 [24] Alabaster, ground [20] Alabaster, boiled [21] Vicron 45-3 [13] Glass flakes [16] Alabaster plaster [19]

ViCALity Ultra Heavy [12] Marblewhite 200 [4] Terra alba [23] Pure Boiled Alabaster

Thassos (0.075-0.15 mm) [10] Thassos (0.425-0.6 mm) [7] Thassos (0.15-0.3 mm) [9] Thassos (<0.6 mm) [6] Marbledust-M [3] Calcite [2] ATF 40 [1] Pure Alabaster

Thassos (0.3-0.425 mm) [8] Baked Thassos [11] Pure Baked Thassos

Pure Thassos

HARD

Gloss (GU)

HIGH GLOSS

Blanc fixe [22] Marbledust-M [3] Vicron 45-3 [13] Calcite [2] Marblewhite 200 [4] Alabaster plaster [19]

ViCALity Ultra Heavy [12]

Ppt. calcium carbonate [5] Aerosil R 7200 [14] Cellulose powder [25] Alabaster ground [20]

Polywax 2000 [24] Pure Thassos

Alabaster boiled [21] Terra alba [23] Thassos (0.075-0.15 mm) [10] Cristobalite [15] Baked Thassos [11] ATF 40 [1] Talc Nicron 400 [18] Glass flakes [16] Pure Alabaster

Thassos (<0.6 mm) [6] Thassos (0.425-0.6 mm) [7] Thassos (0.15-0.3 mm) [9] Thassos (0.3-0.425 mm) [8] K15 glass bubbles [16] LOW GLOSS

Brightness (L*)

LOW

Pure Alabaster

Aerosil R 7200 [14] Cristobalite [15] Pure Carrara

Terra alba [23] Cellulose powder [25]

Polywax 2000 [24] TalcNicron 400 [18] ATF 40 [1] Thassos (<0.6 mm) [6] Alabaster ground [20] Pure Thassos

Alabaster boiled [21] Thassos (0.425-0.6 mm) [7] Thassos (0.3-0.425 mm) [8] Thassos (0.15-0.3 mm) [9] Thassos (0.075-0.15 mm) [10] Marbledust-M [3] Calcite [2] Alabaster plaster [19] Marblewhite 200 [4] Blanc fixe [22] Vicron 45-3 [13] Glass flakes [16] Baked Thassos [11]

Ppt. calcium carbonate [5]

ViCALity Ultra Heavy [12] K15 glass bubbles [17] HIGH

Color (b*)

BLUE

Pure Carrara

Cristobalite [15]

Polywax 2000 [24] Pure Thassos

Cellulose powder [25] Thassos (0.425-0.6 mm) [7] Thassos (<0.6 mm) [6] Alabaster ground [20] Thassos (0.15-0.3 mm) [9] Alabaster boiled [21] Thassos (0.3-0.425 mm) [8] Thassos (0.075-0.15 mm) [10] Aerosil R 7200 [14] Kl 5 glass bubbles [17] Talc Nicron 400 [18] Glass flakes [16] Vicron 45-3[13] Calcite [2] Baked Thassos [11]

Ppt. calcium carbonate [5] Marbledust-M [3] Blanc fixe [22] Pure Alabaster

ATF 40 [1] Marblewhite 200 [4]

ViCALity Ultra Heavy [12] Terra alba [23] Alabaster plaster [19] YELLOW

to shift is also true with brightness (L*) as all of the

formulations decreased in brightness after polishing, with the exception of K15. These observations clearly show that the color of a fill will likely be altered when

finishing it to a high polish.

4. DISCUSSION

The study as presented does not discuss practical appli cations for filling losses in marble; however, it should

be understood that the properties of a fill may be

affected by the method of application. The practi cal application of filling losses will always vary from

conservator to conservator. Fills using bulked Paraloid

B-72 can be applied solid using heated spatulas, as a

wet and runny mixture, or as a thick, wet putty, each

of which would require different tools for application and finishing. The properties observed in this paper are relevant to the specific fill formulations and their

preparation, and a change in these formulations may affect these properties.

5. PRACTICAL TEST ON THASSOS USING THE OPTICAL MEASUREMENTS

A trial was made on a piece of polished Thassos

marble in order to test the formulations having the

closest values with the actual marble for L*, b*,

and translucency. The Thassos was chiseled to make

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JULIE WOLFE

Fig. 7. The set of testing coupons shown in Figure 3, photographed in specular light to reveal variation in achievable gloss from polishing. The surface of each coupon was highly polished overall, and then sandblasted on its right half.

JAIC 48 (2009):121-140



137


eight losses. Alabaster, boiled alabaster, Polywax 2000,

cristobalite, cellulose powder, Thassos (<0.6 mm), Thassos (0.425-0.6 mm), and Aerosil R 7200 had the

closest measurements, as seen in table 3. It is interest

ing to note that none of these fillers was the closest

match for all three of the different measured values

for Thassos marble. The Aerosil R 7200 appeared to

have the best translucency match when examining the fill with a fiber optic source; however, the fill was

brittle, too gray, and hard to carve, making it imprac tical for conservation use. The second and third best

match in translucency were the boiled and unboiled

alabaster formulations. Both alabaster fills gave a nice

color match and were easy to carve and finish. The

Polywax 2000 ranked fourth and was easy to carve, al

beit slightly brittle, but appeared too translucent. The

other tested formulations were too opaque, and very hard to carve and finish.

6. CONCLUSION

This study has allowed for a general comparison between the physical and mechanical properties of

twenty-five different fill formulations in Paraloid B

72 for use in loss compensation on white marble.

PreHminary concentration studies with Paraloid B-72

suggested an ideal resin concentration of 60% w/v in

acetone for all of the fillers included in this study. Filler concentration studies have shown the maxi

mum level of loading capable for each filler, and the

threshold limit is reflected in the final fill formula

tions used for making the test coupons. The work

ing properties of the wet fills vary considerably, and

will affect the application and finishing techniques.

Shrinkage does not appear to be a large problem with

the formulations, except for the Aerosil R 7200. The

formation of bubbles is a problem with all of the

formulations.

The Vickers hardness value for all of the fillers

was found to be near or below that of actual pure Thassos marble; however, the measurements were not

found to correlate with one's ability to actually carve

the fill materials with a scalpel. In fact, many of the

formulations were found to be very difficult to carve

and file. Half of the formulations could not obtain a

gloss close to that of highly polished marble, which

means that other final finishing techniques will be

required to obtain high gloss as needed.

Both boiled and unboiled alabaster showed only

slight differences in properties, which were not

significant enough to warrant making any major distinctions. The unboiled alabaster did have the

positive quality of developing fewer bubbles, however.

Baking the Thassos marble before crushing did not

appear to affect its properties when used as a filler in

Paraloid B-72, except that the baked filler was slightly more yellow.

This study should make it easier to choose a

formulation that will mimic the appearance of marble;

however, the analytical results exclusively cannot be

used for making a final match. Unlike a spectropho tometer, our eyes are trained to interpret the surface

reflectance properties of materials in a psychological

way, making the analytical results difficult to correlate

with what we are actually seeing. The final coupon set can be an excellent visual reference when making

marble fills?much like a palette. For an indoor, white marble in good condition, the formulations

that appear to be the most useful include the alabasters

due to their reflectance properties, relative softness,

high gloss potential, low slump, and good working

properties. The great complexity of a bulked resin system de

mands further study to reach understanding sufficient

to allow conservators to manipulate variables such as

drying rates of these putties, and to address long-term

stability arid reversibility of the fills. Studies including

compressive testing would be useful in evaluating ma

terials appropriate to use for fills requiring structural

strength. With the virtually endless availability of in

dustrial filler products, additional types of fillers could

be compared. Surface modifications, such as silanes,

coupling agents, anti-skinning agents, as well as ad

ditives that improve filler performance, have already been researched for industrial applications. Drawing on these findings and on new research, modified

fillers may be found to improve the workability and

flexibility of the fill material. Comparison studies of

the fillers in different resin systems could also prove useful.

ACKNOWLEDGMENTS

The project was carried out with the assistance of sum

mer intern Talitha O'Conner, without whom sample

preparation, testing, and documentation could not

have been done. The author wishes to thank Brian

Considine, Conservator in the Decorative Arts and

Sculpture Conservation Department at The J. Paul

Getty Museum for his support, as well as numerous

JAIC 48 (2009):121-140



138

JULIE WOLFE

other staff at the museum: Mark Mitton, George

Johnson, Jane Bassett, Arlen Heginbotham, Jessica

Berman, Scott Fife, and Eric Risser. Also thanks to

the scientists at the Getty Conservation Institute, Gi

acomo Chiari, Jim Druzik, Karen Trentelman, David

Carson, Julie Arslanoglu, Christel Pesme, and Ron

SchmidtHng. Valerie Greathouse at the Getty Re

search Institute assisted with the literature searches

on fillers and Paraloid B-72. Dr. Eric Sung, Professor

at the UCLA Dental School instructed and guided the author in the use of the Vickers Hardness Testing instrument. Also thanks to the Conservation Depart

ment of the Detroit Institute of Arts for the loan of

their Novo-Gloss glossmeter for this project.

APPENDIX 1: SAFETY

Since four of the fillers in this study are listed as

California Proposition 65 carcinogens, their concen

tration levels in the air were monitored during sand

ing. The potentially carcinogenic fillers include ATF

40, cristobalite, talc, and VICRON 45-3 according to their Material Safety Data Sheets. A portable Ned

erman air extraction unit with a particulate filter was

used to keep the dust level below the permissible limit

of exposure.

Any silicaceous particle smaller than 10 microns

can travel through the human respiratory system to

the alveoli of the lungs, requiring especially close

monitoring. During the sanding of the coupons, the air close to the face was sampled using a Gi

lair 3 sampling pump set at 2.5 liters per minute,

with a 37 mm, 5 micron PVC filter with an SKC

aluminum cyclone attached. Analysis methods were

NIOSH 600-Gravimetric and NIOSH 7500-X-Ray Diffraction Spectroscopy for silica analysis. Broad

spire/NATLSCO Risk and Safety Services conducted

the analysis. The conclusions on results for the per missible limit of exposure were based on the specific

sanding procedure carried out for this study.

APPENDIX 2: BUEHLER HARDNESS TESTING

The Buehler Hardness testing instrument creates a

136? pyramidal mark with a diamond-tipped inden

ter onto the surface of the sample. The indentations

were made at a range between 25 and 500 gram force

(gf). The length of each diagonal line of the mark

was measured using a graticle and a 40 x oculus. Five

measurements were taken across the face of each sam

ple. The instrument calculates the HV by dividing the force by the surface area of the indentation. Each

coupon had a slightly different resistance to indenta

tion and required different force settings. For example, the harder samples required higher force. A variation

in hardness was found across the surface of some of

the coupons, caused by the range in particle sizes oc

curring in the fillers; therefore, the hardness of some

putties can be rather inhomogeneous on a micro scale.

All of the results were averaged for the ranking tables.

APPENDIX: NOVO-GLOSS TESTING

The Novo-Gloss glossmeter readings were taken from

the polished coupons (to 12,000 grit) before half of the coupon was treated by sandblasting. The meter

was calibrated using a standard. Three measurements

were taken from each coupon, rotating the coupon for

each reading at 20?, 60?, and 85? reflectance angles. Rotation of the sample was in 90? increments, and was

done in case there was a difference in gloss based on

the direction of sanding, or because of small scratches.

After averaging the results for each set of three mea

surements and ranking the fill coupons from matte

to glossy, a slight difference in the order was noted

at each reflectance angle. Since most of the measure

ments at 60? were within the range of 10-70 gloss

units, the results as ranked were presented at this ge

ometry. To back up the GU ranking of the coupon, a visual comparison of the gloss levels was carried out

using the naked eye prior to interpretation of the GU

data, which resulted in the same ranking conclusions.

APPENDIX 4: COLOR READINGS

The CIE L*a*b* readings were taken using an Ocean

Optics spectrophotometer with a quartz halogen fiber

optic system set at 550nm with a daylight 6500K illu

minant and 10 degree observer.

REFERENCES

Gachter, R., and H. Miiller, eds. 1985. Plastics additives

handbook: Stabilizers, processing aids, plasticizers, fillers, re

inforcements, colorants for thermoplastics. Munich: Hanser

Publishers.

JAIC 48 (2009):121-140



139


Gansicke, S., andj. W. Hirx. 1997. A translucent wax

resin fill material for the compensation of losses in

objects. Journal of the American Institute for Conservation

36:17-29.

Griswold, J., and S. Uricheck. 1998. Loss compensa tion methods for stone. Journal of the American Institute

for Conservation 37:89?110.

Hansen, E. E 1995. The effects of solvent quality on

some properties of thermoplastic amorphous poly mers used in conservation. In Materials Issues in Art and

Archaeology IV: Symposium, May 16-21, 1994, Can

cun, Mexico, ed. P. B. Vandiver, J. R. Druzik, J. L.

Galvan Madrid, I. C. Freestone, and G. S. Wheeler,

807?12. Materials Research Society Symposium Pro

ceedings, vol. 352. Pittsburgh, Penn.: Materials Re

search Society.

Larkin, N., and E. Makidrou. 1999. Comparing gap fillers used in conserving sub-fossil material. Geological Curator 7'(2):81-90.

Larson, J. 1978. The conservation of marble monu

ments in churches. The Conservator 2:20-25.

Malaga-Starzec, K., J. E. Lindqvist, and B. Schouen

borg. 2003. Experimental study on the variation

in porosity of marble as a function of temperature. In Cultural Heritage Research: A Pan-European Chal

lenge, ed. R. Kozlowski. Luxembourg: Office for

Official Publications of the European Communities.

305-08.

Nagy, E. 1998. Fills for white marble: properties of

seven fillers and two thermosetting resins. Journal of the America Institute for Conservation 37:69-87.

Plueddemann, E., and G. Stark. 1977. Surface mod

ifications of fillers and reinforcement in plastics. In

Discover Reinforced Plastics: Technical Proceedings, 32nd

Annual Conference, SPI Reinforced Plastics/Composites Institute: February 8-11, 1911, Washington, D.C. New

York: Society of the Plastics Industry. 4-C-l to 4-C-9.

Pullen, D. 2004. Personal communication. Head of

sculpture conservation at Tate in London.

Solomon, D. H., and D. G. Hawthorne. 1983. Chem

istry of Pigments and Fillers. New York: John Wiley &

Sons.

Vail, C. 2005. Electronic correspondence. Regional Sales Manager, Aerosil & Silanes, Degussa Corpora tion (now Evonik Degussa), Laguna Niguel, Calif.

SOURCES OF MATERIALS

Alabaster, Thassos marble, Cararra marble

Carnevale & Lohr, Inc.

6251 Clara St.

Bell Gardens, CA 90201

(562) 927-8311

ATF 40, Vicron 45-3, Marblewhite 200, ViCAL

ity Ultra Heavy PCC

Specialty Minerals

260 Colombia St.

Adams, MA 01220

(413) 743-0591

Marble dust-M, calcite, cristobalite, glass flakes

Kremer Pigments Inc.

228 Elizabeth St.

New York, NY 10012

(212) 219-2394

Carbon steel surgical blades #15, precipitated cal

cium carbonate, Polywax 2000, Paraloid B-72

Conservation Support Systems 924 West Pedregosa St.

Santa Barbara, CA 93101

(805) 682-9843

Pumice (medium) Conservation Materials (now: Conservator's Em

porium) 385 Bridgepoint Dr.

South St. Paul, MN 55075-2466

(800) 672-1107 Fax: (651) 554-9217

Whatman ashless cellulose powder, acetone

Thomas Scientific

P.O. Box 99

Swedesboro, NJ 08085

(800) 345-2100

Nicron 400

TAP Plastics Inc.

Dublin, CA 94568

(800) 246-5055

www.tapplastics.com

Aerosil R 7200

Evonik Degussa

JAIC 48 (2009):121-140



140

JULIE WOLFE

2 Turner Place

Piscataway, NJ 08855

www. evonik. com

K15 3M 3M Center

St. Paul, MN 55144-1000

(651) 737-6501

JULIE WOLFE has a BFA in art history from the

University of Illinois in Champaign-Urbana. She

graduated in 1997 with an MA from Buffalo State

College, specializing in objects conservation. She ob

tained advanced training in conservation at the

Straus Center for Conservation, Harvard University Art Museums. Past experiences include working at the Williamstown Art Conservation Center in

Massachusetts, the Harvard-Cornell excavation in

Sardis, Turkey, and the Solomon R. Guggenheim Museum in New York. She is currently an asso

ciate conservator at The J. Paul Getty Museum in

Decorative Arts and Sculpture Conservation. Address:

The J. Paul Getty Museum, Decorative Arts and

Sculpture Conservation, 1200 Getty Center Drive,

Suite 1000, Los Angeles, CA 90049, 310-440-7266;

j wolfe@getty. edu

JAIC 48 (2009):121-140



effects of bulking paraloid b-72 for marble fills

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