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IN SITU ASSESSMENT OF SURFACE CONSOLIDATION AND PROTECTION TREATMENTS OF

MARBLE MONUMENTS IN ROME OF THE 1980'S, WITH PARTICULAR REFERENCE TO TWO TREATMENTS WITH PARALOID B 72.

ROBY, THOMAS C.

c/o American Academy in Rome, Via Angelo Masina 5, 00153 Roma, Italy

SUMMARY

A comparative assessment of surface consolidation and protection treatments of the past ten

years on marble monuments in Rome, based on primarily on visual examinations, has shown the need

for maintenance and re-treatment, particularly regarding protectants, whether they are siloxanes, acrylic

resins or lime-based. A more in-depth evaluation of two monuments treated with Paraloid 872, the

Temple of Vespasian and the Column of Foca, demonstrates the difficulty of accurate in-situ testing, when no prior tests exist for comparison, and current methods are not adequate.

At tempts are made to explain the very different results of these two treatments after ten years, which

according to unpublished documents are virtually the same .

. INTRODUCTION

The original intention of the research, begun as a Fellow in Conservation at the American

Academy in Rome, was to assess the condition of ancient marble monument surfaces treated with three

different consolidant and protectant materials employed during the 1980's in Rome.

The consolidants included an acrylic resin co-polymer in solution (Paraloid 872), an inorganic

consolidant containing silicic acid ester plus a catalyst (Wacker OH), and a traditional material, lime

water (from slaked or hydraulic lime). As protectants, monuments in the same period were treated after

conservation programs with either Paraloid 872, or a semi-transparent lime wash, or a siloxane water­

repellent (Wacker 290L or 280). At the time there was considerable debate among the conservation

authorities and conservators involved regarding the choice of materials, and in some cases changes in method occurred during the period of treatment of the same monument. Ten to fifteen years later the

monuments of Rome provide an excellent opportunity to learn from past experiences and observe how

the different conservation materials have performed long-term in situ in a polluted environment.

The methodology of the planned evaluation consisted of 1) a review of published treatment

reports, 2) consultation of more detailed archival documentation kept by the local administration and/or

the private company's records, especially in cases where no publication exists. 3) a visual examination

and assessment of the monument surfaces, and 4) in situ testing (1).

Completing the second phase was very problematic, however, as obtaining access to archival graphic

and photographic documentation, and treatment reports from the appropriate administrative authorities

or private companies proved difficult and sometimes impossible. Therefore, most of the information

regarding recent treatments in Rome was obtained from publications(2). These sources revealed that conservation treatments of monuments in Rome during the 1980's

witnessed the increasing use of Wacker OH for the surface consolidation of marble, which replaced

Paraloid 872, and in some cases was used in conjunction with lime. Although Wacker OH has been recommended by the manufacturer and conservation scientists in the

past for use on sandstone in particular, it has been chosen for use on marble for a variety of reasons, including its lack of observed color alteration over time in situ, ease of cleaning after use for pre~

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consolidation, and by now, its proven track record on marble surfaces, except those severely lacking in

cohesion.

In addition, several conservators during this period used only lime-water as a consolidant, and reported

its effectiveness. It is interesting to note the regional aspect of these choices of materials within Italy. In

Venice, for example, neither Wacker OH nor lime has been used in consolidation treatments of marble

monuments at all in the same period (only on one monument, the facade of the church of S. Salvador,

was Wacker OH used, and in this case on Vicenza limestone by a company from Rome)(3).

The use of water-repellent protectants has become increasingly commonplace in Rome since

the mid-1980's, with a clear preference for siloxanes.

The majority of these treatments have utilised Wacker 280 (formerly 290L), although Paraloid 872 was

frequently used until the mid-1980's, while lime-based shelter coats, or scialbature, in imitation of

traditional methods of protection (4), have also been chosen by a few conservators. Several significant

monuments were not treated with any protectant (5).

CONDITION SURVEY

The preliminary research and visual inspection of treated surfaces was carried out also in

connection with a national survey of treated monuments undertaken by the Italian National Research

Council (CNR) and the Federation of European Chemical Societies (FECS). The information on

treatments obtained from publications, and from archives when made available, was compiled on data

sheets (CNR- Firenze, Centro di Studio sulle Cause di Deperimento e Metodi di Conservazione delle

Opere d'Arte) for the different monuments.

Subsequent visual examinations were carried out, using binoculars when necessary, and FECS

condition survey forms were filled in for each monument (6). The survey form was developed from

those intended to simply assess the condition of monument surfaces. As a result, certain types of

deterioration listed on the form were impossible to assess as occurring after treatment without being

very close to the stone surfaces or without having detailed photographic documentation taken after

treatment to consult during the survey.

For example, how can surface powdering be determined except by touching the surface; or how can

pitting or staining be determined to be on-going since the last treatment without having photographs in

hand to compare at close observation; and how can one assess surface color change without having

untreated surfaces or color measurements taken after treatment as a reference, which is rarely the

case. Despite the limitations on access to condition documentation immediately after treatments, and to

the monument surfaces themselves, the forms were compiled as much as possible and then provided

to the survey co-ordinator for Rome, Dr. Laurenzi Tabasso.

ASSESSMENT

The visual surveys carried out over 1994-96 benefited whenever possible from close-range

inspection due to the presence of scaffolding, or to the existence of internal stairways. A summary of

observations regarding recent consolidation and protection treatments on marble monuments in Rome follows.

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CONSOLIDATION

Although the assessment of consolidation treatments was limited to surfaces that could be

examined manually, it was possible to confirm that several treatments with Wacker OH (Temple of

Hercules Victor or Tempio Rotondo in the Forum Boarium, and Michelangelo's Statue Base of Marcus

Aurelius in Piazza del Campidoglio) in 1990-1991 are still in good condition.

The localized areas consolidated with the product showed no new signs of surface powdering or color

alteration. In the case of the Statue Base, the treatment was protected with a lime-based shelter coat,

while at the Tempio Rotondo, no protectant was applied, so that its consolidation performance can be

evaluated on its own without the influence of a subsequent protection treatment (7-8).

The common use of a protectant after consolidation makes an evaluation of a consolidation

treatment even more difficult without the aid of sampling and destructive testing.

Three monuments in Rome were not treated with a protectant in the 1980's after localized applications

of two different consolidants, lime water (Arch of Septimius Severus and Temple of Saturn-second

phase) and Paraloid B72 (Column of Trajan-first phase) (9), but access to the consolidated areas was

unfortunately not possible without scaffolding or a jib.

However, an evaluation three years after the lime water treatment of the Temple of Saturn by the same

conservator in 1990 revealed renewed surface powdering and scaling. Re-treatment was subsequently

carried out where needed. (10) While OH appears to perform better over time than lime water, and

does not cause the whitening of surfaces, B72 used alone as a consolidant has not been examined from

close range. In cases where it has been protected by either a siloxane or another application of 672, it

has been observed to have darkened (part of the Column of Marcus Aurelius), or is no longer effective

after ten years or less (podium of Column of Foca) (11 ). Treatments with B72 are discussed in more

detail below.

PROTECTION

The survey of approximately 30 monuments has shown that all three protection materials used

in the 1980's in Rome, acrylic resin (B72), lime-based shelter coats and siloxanes (280, 290L), generally

lose their effectiveness within five years or less, depending on the micro-environment.

A comparison of the surface condition of the tops of the Columns of Trajan and Marcus Aurelius

showed that since the removal of the scaffolding around 1988, the unprotected Column of Trajan has

suffered a small, millimetric amount of surface erosion, as evidenced by some surface powdering and

by mortar repairs now laying slightly above level. While at the Antonine Column, treated with 290L,

there is only a slight evidence of surface powdering upon touching, and the micro-mortar repairs are still

level with the stone surface. However, an approximate evaluation of 290L's continued effectiveness

using a water sprayer showed that the surface no longer visibly repels water.

In less exposed conditions, the same protectant, applied to the Base dei Decennali in the Roman Forum

in the same year (12), still visibly repels water when tested in the same way. Since the longevity of

treatments appears to depend largely on the severity of the micro-environment, each individual

protectant treatment must therefore be monitored to determine its effective life span.

A negative aspect of both the siloxane and acrylic resin water repellent treatments is the

formation of dark, parallel, vertical lines on surfaces not exposed directly to rain. The lines are caused

by the channelling of water on the repellent surfaces and the resulting deposition of particulate matter

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on the flow lines. This unnatural surface weathering is disturbing to the trained eye, but the dark lines

can be removed by brushing.

It has also been observed that the acrylic and siloxane treatments can cause a darkening and/or

yellowing of marble surfaces over time. While it was not possible to confirm these observations through

color change measurements regarding siloxane treatments. published natural weathering tests do

support them (13).

Regarding color changes of acrylic resin treatments, visual examinations have shown variable

results after ten years, depending, in some cases, on the different concentrations of B72 (between 2%

and 15%) that were employed. The observed connection between B72 concentration and color change

is supported by a recent study on weathering of acrylic protectants (14). In situ color tests of two acrylic

treatments are being performed to quantify the observations and provide a comparison to such

laboratory studies on samples. which are discussed below.

The change of surface appearance which results from treatment with a lime-based shelter coat

as a protectant is clearly a negative aspect of this material.

Its semi-transparent nature. however, has been used to advantage where monument surfaces were

dishomogeneous in appearance after cleaning, and therefore benefited aesthetically from a non­

transparent coating (sculptural reliefs of the Arch of Titus, statue base of Marcus Aurelius, and the

Stadium of Domitian)(15-18).

Tests of lime shelter coats were carried out on parts of three monuments in the 1980's, the capital of the

Column of Foca, one of the Dacian sculptures of the Arch of Constantine, and one of the capitals of the

Temple of Hadrian (19). The treatment of the first appears from a distance in good condition today, but

the lime wash was itself protected by an application of B72 at 3% (20). The only treatment possible to

examine well from the ground is the Statue Base of Marcus Aurelius, where, after five years of exposure,

there is little visible evidence left of the lime wash application.

The surprisingly short period of effectiveness of all protection treatments, as demonstrated both

in situ and in tests (21-22). particularly in an aggressive environment such as occurs with fountains (23), presents the need for re-treatment.

However, sufficient research has not been carried out so far on the long-term effects of re-treatment.

Laboratory tests of the reversibility of different protectant materials after weathering have shown that

acrylics and siloxanes do not perform well (24 -26), indicating that accumulations of protectant

materials could occur in the pores of the stone with unknown consequences.

Although the protective effect of a sacrificial layer of calcite has not been tested, the presumed

reversibility of a lime wash make it a viable option for monuments in an unaggressive environment until

we know more about the effects of protection re-treatment on stone already treated with acrylic or siloxane protectants.

IN SITU TESTING

The 1995 ICCROM Colloquium. "Methods of Evaluating Products for the Conservation of

Porous Building Materials in Monuments", confirmed that there are a very limited number of in-situ tests

available to evaluate the performance of materials used in past treatments on monuments, despite their

importance to any treatment assessment. More tests would be available, particularly regarding

consolidation treatments, but many of them are destructive, requiring sampling, or are damaging.

Important studies have been done in the past using destructive methods (27), but attitudes have

changed regarding testing, and it is justifiably more difficult to obtain permission for sampling. Tests of

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consolidation are also complicated by the fact that in many cases a protectant was applied subsequently

which will influence any surface evaluation. Ultrasonic velocity testing is available, but it is useful for in­depth, rather than the more common surface consolidation treatments, and it requires previous testing

for comparison.

In cases were consolidation was carried out using products which also have hydrophobic

properties or are combined with a water repellent, these treatments can and have been evaluated in situ

quantitatively by water absorption tests using a pipette (28 - 29), or visually using a sprayer. The change

of color of surfaces that have been consolidated can be recorded quantitatively in situ using colorimeters

(30), or by visual comparison with color reference charts (Munsell). To evaluate past surface protection

treatments in situ. there are basically the same possibilities, water absorption to determine the

treatment's effectiveness in repelling water, and change of color to determine one possible negative

impact of the treatment (31-33).

Obviously, these tests require comparable data before and ideally after treatment so that comparisons

can be made, or at least the presence of untreated areas of surface as a control reference.

The 1995 ICCROM Colloquium also revealed that it has been very difficult in the past for

external researchers to obtain both the pertinent information regarding past treatments, access to the

monuments. and permission to present the findings. As a result, the rare examples of published

evaluations of past treatments are done by those individuals involved in the original treatment, or the

responsible institutions (34-35). Such 'self-evaluation' has practical advantages due to the unique

familiarity that those originally involved have with the past treatment. These types of studies should be

encouraged in the future, but at the same time external researchers, including conservators, should also

be allowed more frequently to pursue and publish their own assessments in co-operation with the

responsible authorities. The permission to carry out the following non-destructive testing and evaluation of two marble

monuments in Rome treated with an acrylic resin as a consolidant and protectant in the mid-1980's

represents a significant step in collaboration between conservation authorities, scientists, and

conservators, which can only benefit the profession.

In situ evaluation and comparison of two treatments with acrylic resin (Paraloid 872).

INTRODUCTION

The use of Paraloid 672 for consolidation and protection treatments of outdoor marble

monuments has a rather long history in Italy, given the conservation profession's relatively short period

of existence. Already in the late 1960's, after years of testing (36), the preliminary consolidation of marble reliefs in

the portal of the Duomo of Siena was carried out under the direction of Paolo Mora of the lstituto

Centrale del Restauro, after a further in situ test, using Paraloid 672 (5% in xylene) (37).

Continuing in the 1970's in Venice, lstituto Centrale del Restauro worksites used 672 as a temporary

consolidant (Lunette of Scuola Grande di S. Marco, 1973) and as a consolidant and protectant (Portal of

the Arsenale 1974). Also in Venice, the statue base of Bartolomeo Colleoni in Venice was treated by a

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private company using 872 as a consolidant and protectant (15% and 5% respectively in chlorothene) in

1978 (38).

By the beginning of the 1980's conservation companies composed of former lstituto Centrale

students and others were commonly using 872 for the consolidation and protection of outdoor marble

monuments in and near Rome (facade of the Duomo of Orvieto, Forum of Nerva-initial phase, Porta del

Popolo, Arco degli Argentari, Arco di Giano, etc.) (39). The percentage of 872 in solution that was

employed in treatments through the mid-1980's varied from monument to monument, particularly

regarding protection (generally 2-7% in increasing concentrations for consolidation, between 2-15% for

protection), but the solvent used was almost always chlorothene (trichloro ethane) or a mixed solvent

nitro cellulose paint thinner, diluente Nitro. These treatments were undoubtedly influenced by a 1981

lstituto Centrale del Restauro study of 872 and 844 acrylic resins, which recommended their use for

consolidation and protection of marble at 10% in chlorothene (40).

In 1985, a collaborative lstituto Centrale study on 872 showed that wet/dry cycles significantly

decreased its water repellency after being applied to limestones, indicating its effectiveness as a

protectant outdoors would be short-lived (41).

In the same period in Rome, observations by conservators of areas on marble monuments previously

treated with 872 as a preconsolidant or temporary treatment, showed that they became dirty and

darkened over time, and could only be cleaned by removal of the 872 with a solvent (42). As a result,

many worksites on marble monuments in Rome stopped using 872 as a consolidant and protectant.

This dirtying phenomenon of 872 has never be studied, but natural weathering of four different

protectants, two of which contained acrylic resin as a component, showed that those containing the

acrylic resin attract and retain dust/particulate matter to a much higher degree, as well as becoming

slightly yellow. Significantly, this study also showed that "after two years of outdoor exposure and after

artificial ageing, the protective action of all the tested treatments decreases, and in some cases even

disappears" (43).

Despite experimental studies from the mid-1980's confirming the overall reversibility and stability

under UV radiation of 872 mixed with silicone resin (44-45), more recent laboratory investigations have

identified UV radiation as a factor in chemically and physically damaging acrylic resins, including 872,

thereby causing them to become, among other things, less soluble (46), particularly at low and medium

RH levels (47). These experimental results could explain one conservator's recent experience of being

unable to remove a darkened consolidation test with an unidentified acrylic resin (872?) on the Arch of

Titus, despite various attempts with poultices of different unidentified solvents (48).

These negative results from studies and practical experience in work sites during the past ten

years involving acrylic resins, and 872 in particular, both as a consolidant and protectant, has convinced most conservators by now to no longer use it outdoors on monuments.

Yet in some observed cases, the use of 872 in the past has been effective without producing visibly

negative results over time, such as a significant darkening of surfaces. The evaluation of two marble

monuments in the Roman Forum treated with 872 at approximately the same time and in approximately

the same manner, but with very different surface conditions ten years later. provides an opportunity to

determine what factors make the results of its use satisfactory in some cases, and in others not, while

providing indications for the future maintenance of these and other monuments similarly treated.

-Preconsolidation with 3-10% solutions of Paraloid 872 in chlorothene (3-5% in trichloro ethane

according to archives), and emergency facings with Japanese paper or cotton gauze and 872 at 15%.

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-Consolidation of entire surface with 3-5% solutions of 672 in chlorothene.

-Protection of entire surface with 3-5% solutions of 672 in chlorothene, including capital also treated with

a lime wash as a protective, sacrificial layer. Reversibility of both types of protectants tested with

satisfactory results after application.

-Application method: 672 by brush, lime wash of capital by spray. -Treatment period: 1981-1985,

protection: September, 1985.

-Marble: Mt. Hymettus (Athens), identified by Corrado Gratziu, geologist, University of Pisa.

The marble of the podium. however. appears to be different, as it lacks the strong veining of the column

itself.

(Sources: Monument Treatment Form, Archive of Soprintendenza Archeologica di Roma; treatment

report of conservation company, "Eleazar", January, 1986; personal communication, conservator

Daniela Bartoletti, formerly of "Eleazar". May, 1996).

-Preconsolidation with 3-5% solutions of Paraloid 672 in trichloro ethane (chlorothene), emergency

facing with Japanese paper and Gelvatol 40-20 {polyvinyl alcohol) at 10% in water and ethyl alcohol.

-Consolidation with 5-7% solutions of 672 in trichloroethane (3-10% according to archives).

-Protection with 2% solution of 672 in trichloro ethane "with possible increase in percentage" according

to co-chief conservator of conservation company, "Corest", Stefano Provinciali (3% according to

archives).

-Application method: consolidation by brush, protection by spray. -Treatment period: 1982-87,

protection: August-September, 1987.

-Marble: Luni (Carrara)

(Sources: Monument Treatment Form, Archive of the Soprintendenza Archeologica di Roma; personal

communication, Stefano Provinciali, partner of conservation company, "Corest", May, 1996; L. Lazzarini,

M. Pecoraro. and P. Pensabene, "Determination of the Provenance of Marbles Used in Some Ancient

Monuments in Rome", in Classical Marble: Geochemistry, Technology and Trade, eds. N. Herz and M.

Waelken (Dordrecht, Kluwer, 1988) 399-409.

IN SITU EXAMINATION

A close inspection of the podium of the Column of Foca and the lowest portions of the three

columns of the Temple of Vespasian in March,1996 permitted the following observations and

comparisons. Since neither the footing of the podium of Foca nor the bases of the columns of Vespasian have been

treated according to documentation and to the conservators involved (the location of the scaffolding

interfered with treatment), these lowest sections of the two monuments offer before-treatment

references for the rest of the surfaces treated as recorded above. However, observation of the footing

block of the podium of Foca reveals that it has recent mortar repairs, suggesting that it may also have

been treated with 672 as was the rest of the monument.

I. COLUMN OF FOCA

SURFACE CONDITION A tactile testing of the podium showed that certain blocks exhibit severely powdering surfaces.

others are slightly powdering, including the presumed untreated footing block. while other blocks are

sound. Therefore there does seem to be any difference between treated and untreated surfaces at the

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base of the monument. The variable conditions of treated blocks appear to be related less to

differences in environmental exposure, than to the natural geological differences between the blocks, all

presumed to be quarry variations of the same marble.

Observations of micro-mortar repairs reveal that some surface erosion of treated blocks has already

taken place, particularly on the SE face, as evidenced by the fact that some of the repairs are slightly

above the level of the immediately surrounding stone.

On the same face, the partial pealing off of the surface of a large mortar infilling between blocks

has been noted. This is probably due to the application of B72 as a protectant forming a skin on the

mortar repair surface, which after ten years is becoming detached. Other mortar repair surfaces on the

podium are partially covered with a black patina of algal growth, further indicating that the protection

treatment has not been effective as a water repellent already for some time. This observation is

additionally supported by evidence of black crust formation on the NW side of the podium.

Observation with binoculars of the surface condition of the capital, treated with a lime wash and

protected with 872, shows localized white areas due perhaps to the loss of B72 and some dark areas

due to superficial deposits, but the lime wash is still visible as an opaque layer on the areas of greatest

surface damage.

CHANGE OF COLOR

There is no visibly discernible color difference between the treated podium and untreated

footing of the monument. Readings with a Munsell Soil Color Chart on the different treated blocks on all

four sides were taken. Most of the readings were SY 8/1 (SE, NE and NW faces), but one block was

closer to 2.S Y 8/0 (NE face) , while another was closer to 7.S YR 8/0 (SW face) . These differences are

attributed to the different colors of the indMdual blocks composing the podium, rather than to the

different environmental exposures on each side of the podium. The reading of the untreated footing

block was also SY 8/1 .

More precise readings were taken in June, 1996 with a Spectrophotometer (Minolta CM-2002)

of treated and untreated areas of two sides (SE and NE) of the Column podium (see Tables 1-6).

Points SE/1 and NE/1 are of the untreated footing block, while the other points are located in treated

blocks above. The two sides were chosen on the basis of different environmental exposures, but the

choice of points was arbitrary as the surfaces are very unhomogeneous. As expected. the inconsistancy

of the results make any conclusion concerning color alteration of the treated areas impossible. This is

due to the variation of color within each block, and to the fact that the untreated reference area is a

different block of marble. In fact according to the results, the footing block is darker than the treated

blocks, which is the opposite of what one would expect. The inconclusive measurements reflect the

visual assessment of no distinction between treated and untreated areas, indicating that the B72 is no longer present on the surfaces.

WATER REPELLENCY

Preliminary estimates of the water repellency of the treated surfaces were obtained using an

ordinary hand sprayer on all four faces. No visible evidence of water repellence in the form of beading

up or slowness in absorption was observed, nor was there a visible difference between the result of spraying treated and untreated areas.

1023

Water absorption tests with the pipette method are planned to obtain more precise data and to

determine if any of the 672 is still present on the surfaces and having an effect on water repellency.

II. TEMPLE OF VESPASIAN

SURFACE CONDITION

A tactile testing of the surfaces of the lower zones of the three columns revealed that there is no

evidence of surface powdering on the accessible sides of the treated columns. In contrast, the

untreated column bases do reveal a lack of surface cohesion. Treated surfaces show virtually no signs

of biological growth or black crust formation, as do the untreated bases.

There is, however, a marked difference between the treated and untreated parts of the columns in

terms of color. The treated column shafts have darkened considerably in relation to the untreated

bases.

CHANGE OF COLOR

Preliminary measurements of color were taken in March, 1996 with reference to the Munsell

Soil Color Chart. Column C (NW), SE side: 10 YR 7/1 - treated, SY 8/1 - untreated areas of column and base. Column B (Nor middle), SW side: 2.SY 712 - treated, 2.SY 8/0 - untreated base. Column A (SE),

NE side: SY 6/1 - treated, 10 YR 8/1 untreated base. These readings confirm the visual observation of

the significant difference between treated and untreated areas, and that the sides of the treated columns

more protected from the environment (NE) are slightly darker than the more exposed sides (SE).

In June, 1996 more precise measurements were carried out with a Spectrophotometer (Minolta

CM-2002) on the lower sections of two of the columns (see Tables 1-6). The SE side of Column C and

the NE side of Column A were chosen for reasons of accessibility and interest in comparing more and

less exposed surfaces.

Points C4, CS, C6, and A1, A2, A3, represent points on the treated columns, while points C1,

C2, C3, and A4 and AS are points on the untreated column base blocks. The results expressed in terms of brightness (Y%), reflectance (R%), whiteness (W1(ASTM E313)) and yellowness (Y1 (ASTM E313

and 01923)) provide some evidence that the treated areas have darkened and yellowed in relation to

untreated areas, with the particular exception of point CS, which has approximately the same values,

and point C6, which has values even brighter and whiter than the untreated column base. However, the

inconsistency of the results, particularly regarding the reference readings of the untreated bases, and

the small number of points measured, make it impossible to draw any clear conclusions. The

inconsistency is again due to color variation within the marble itself, and to the fact that different blocks

of the same marble were used for comparisons of treated and untreated areas. The measurements would be more conclusive if one accepts the likely hypothesis that point C6

represents an unintentionally untreated area of column C. A comparison with CS, located within several

centimeters of C6, in terms of "total color difference" - dE* is 8.7, which represents a significant

difference between treated and untreated zones. The more protected surfaces of points A1-AS of

Column A provide an even more marked difference between untreated and treated areas. Although the

dE* of the two untreated points of the base is large at S.6, a comparison of the median treated point A 1

with the untreated A4 and AS points produces a significantly larger dE* at 12.1 and 1 S.2 respectively. Looked at in this way the readings provide more indicative quantitative results to support the visual

1024

impression of considerable darkening of treated surfaces, especially those more protected from the environment

WATER REPELLENCY

Preliminary estimates of the treated surfaces' water repellency were carried out using a bottle

sprayer. On column C, SE side, water appeared to be absorbed more slowly on treated surfaces than

on the untreated base.

On column B, SW side, similarly, water appeared to be absorbed more slowly on treated surface than

on untreated base. On column A, NE side, drip lines formed on the treated surface revealing it to be the

most water repellent area in relation to other treated areas. Although more precise water absorption

measurements using the pipette method were planned, the lack of sufficiently large flat surfaces on the

columns make this an impossibilty.

DISCUSSION

The preliminary in situ tests of the Temple of Vespasian suggest that there is a connection

between the darkness of the surfaces and the continued effectiveness of B72 as a water-repellent and

consolidant, as suggested by a recent laboratory study of acrylic protectants (49).

The darker surfaces generally correspond to those which are still visibly water repellent, which are also

those more protected from the environment. Attempts to quantify the darkening of the treated surfaces

were frustrated by the absence of color readings carried out before and immediately after treatment.

Using untreated adjacent base blocks of the same veined marble as the comparison for readings of

treated surfaces proved problematic.

A visual and tactile examination of the two monuments reveals that there is more B72 remaining

in and on the treated surfaces of the Temple of Vespasian. This is reflected in the overall better

condition of Vespasian's treated surfaces. On the other hand, its surface color has changed

substantially over time, while the Column of Foca's has not. Although more effective as a consolidation

and protection treatment at present, aesthetic considerations make the treatment of the Temple of

Vespasian generally less successful

It is difficult to determine the reasons for the different results of basically the same two

treatments, as revealed by the available information. A comparison of the treatment methodologies

reveals that higher percentages of 872 were used for preconsolidation for Foca, while lower ones were

used for its' consolidation.

But perhaps more importantly, the percentages used for protection were approximately the same for

both the Column of Foca and Temple of Vespasian. Looking at other parameters, the micro­

environment of the two monuments could be a factor. They are basically the same, however, as both

monuments are located in the Roman Forum, although the Column of Foca is more exposed on all

sides. The two years difference between the two treatments could be a factor, but the contrast between

the surface condition of Foca and Vespasian is too marked to be solely a question of time. A difference

in the porosity of the two stones could be a factor, but although the provenance of the marble appears to

be different from the available information, it is unlikely that there is a substantial difference in their porosities, and therefore in the amount of B72 they would absorb.

Different climatic conditions during treatment could be a factor as well, but it appears that they were both

treated for protection around September, so the rate of absorption of the solvent during treatment should have been approximately the same.

1025

The only other possible factor could be a difference in the method of application, but both

consolidation treatments were applied by brush. The protection treatments, however, did employ

different methods. At the Temple of Vespasian, it was carried out at 2 or 3% by spray, which should

have insured a thin, even application. Personal communication with the chief conservator of Vespasian.

however, left some doubt about the precise concentration of the B72 solution in all cases during the protection treatment.

This imprecision, together with the higher percentage used for consolidation (5-7%, as compared to 3-

5% for Foca) could in the end be the determining factors in explaining the darkening of the surfaces of

Vespasian, as has occurred similarly on another Roman monument (Arch of Janus) partially treated at

the same time with much higher concentrations (10-15%) of B72 as a protectant. It should be noted that

precise concentrations of B72 are difficult to maintain outdoors where heat can cause the rapid

evaporation of the solvent during treatment, unless continual care is taken by the conservators.

CONCLUSION

To learn from past conservation experiences, accurate and correct evaluations and

comparisons of treatments of exterior monuments are needed. This requires precise information about

the characteristics of the material before treatment, the treatment methodology, and the environmental

conditions during treatment, which is not always available.

Although Paraloid B72 is no longer used in Rome on exterior monuments, either as a

consolidant, or particularly as a protectant, due mainly to the negative personal experiences of

conservators during the 1980's, we are at present faced with the need for the maintenance of

monuments treated with it.

Monument surfaces treated with Paraloid B72 ten years ago currently show evidence either of

surface powdering or darkening, depending generally on the concentrations of 872 used for

consolidation or protection. The extent of darkening appears also to be linked to the environment in

terms of levels of particulate matter pollution and degree of exposure to weathering.

In the case of either surface powdering as at the Column of Foca, or darkening of surfaces as at

the Temple of Vespasian, the future maintenance of the monuments requires re-treatment in order to

arrest the powdering and loss of material, or to correct aesthetic damage caused by the darkening of

the 872.

Prior to re-treatment, it will be necessary to remove residual remains of the B72 on both

monument surfaces, presumed to be much greater on the darkened surfaces of the Temple of

Vespasian.

In situ tests are required first to determine how the removal of B72 in situ can be carried out most

effectively, as difficulty in extracting B72 after many years on surfaces has been reported.

Laboratory tests are also needed to evaluate the effects of re-treatment on marble surfaces

previously treated with B72, before it is undertaken. It is hoped that the information obtained from the visual and quantitative testing on two Paraloid

872 treatments will provide some useful reference data for future testing of the treatment's long-term

performance, and will encourage future maintenance projects on these monuments, while providing a

comparison with in-situ assessments of other conservation materials on other monuments being carried

out either by the tstituto Centrale def Restauro, ICCROM, or the Soprintendenza Archeologica di Roma.

1026

ACKNOWLEDGEMENTS

The author gratefully acknowledges the assistance and co-operation of the staff of the

Soprintendenza Archeologica di Roma, in particular Conservator C. Conti and Architect G. Martines, as

well as Prof. A. La Regina, Architect M. G. Filetici and Architect Tedone.

At ICCROM, I am indebted to Dr. M. Laurenzi Tabasso for allowing me to participate in her research

activities together with Dr. D. Poggi, and for her assistance, and to Dr. E. Borrelli, particularly regarding

his availability for the color tests. I am grateful to Dr. U. Santamaria of the lstituto Centrale del Restauro

for his interest in carrying out the water absorption tests. Additional thanks go to the staff of the Musei

Capitolini, including Dr. M. Dellera. Fellow conservators D. Bartoletti, S. Provinciali and G. Storace, M.

G. Chilossi, G. De Monte. and M. P. Alessandri have been generous in providing information during my

research.

I wish to acknowledge as well the help of L. Lazzarini, particularly for his initial advice and

encouragement. and the kind assistance of Prof. Malcolm Bell and Director Caroline Bruzelius of the

American Academy in Rome.

Notes

1 The methodology follows in part the example of G. Fazio, "Sull'efficacia di alcuni trattamenti di

restauro realizzati dopo ii 1960" in Bolletino d'Arte, Supplemento al N. 41, 'Materiali lapidei, problemi

. relativi allo studio del degrado e della conservazione', Vol. II (1987):197-214.

This evaluation benefited from information gathered on recent treatments of monuments in Venice by L.

Lazzarini, "Treatment Cards of Venetian Monuments and Sculptures", (Conference material from Third

International Congress on the Deterioration and Conservation of Stone, Venice, 24-27 October, 1979).

2 Of the many published treatments consulted, the most useful was a summary of recent treatments in

Rome by M.G. De Monte, "Consolidanti e Protettivi: Esperienze e Risultati degli Ultimi Anni sui

Monumenti in Pietra all'Aperto", in La Pulitura, ii Consolidamento e la Protezione della Pietra: Problemi

Applicativi. Primo lncontro Tecnico Nazionale Tra Restauratori, Pisa, ARI, 1992.

3 Fassina, V., June,1995. Personal Communication. Chemist, Laboratorio Scientiflco, Soprintendenza ai Beni Artistici e Storici di Venezia, Italy.

4 L. Lazzarini and 0. Salvadori, "A Reassessment of the Formation of the Patina called Scialbatura",

Studies in Conservation 34, no. 1, (1989) 20-26.

For a more complete and up to date account of studies relating to the subject of oxalate layer or patina

formation on surfaces, see Proceedings of the International Symposium, "The Oxalate Films: Origin and

Significance in the Conservation of Works of Art" (1989), and the Proceedings of the Second

International Symposium, "The Oxalate Films in the Conservation of Works of Art" (1996), Milan, Centro CNR "Gino Bozza".

5 For a more general review of recent protection treatments in Mediterranean countries, see G.

Alessandrini. and M. Laurenzi Tabasso, "The Protection of Stone: The Current Situation in Italy and the

Mediterranean Countries", in Science and Technology for Cultural Heritage, 2, (1993): 191-200.

6 For a similar but more extensive example of a data sheet, condition survey form, and condition survey

methodology implemented on a survey of Roman facades in1986-88, see V. Cazzato, e P. Petraroia,

"Monumenti e lnquinamento: Teoria e Prassi nel Dibattito sul Restauro"; G. Fazio, M. Laurenzi Tabasso,

A. M. Mecchi, "Facciate romane: un approccio alla valutazione degli effetti dell'inquinamento

atmosferico"; and "Facciate romane: le schede", in Citta inquinata, i monumenti, eds. A. Montanari e P.

Petraroia, (Roma: lstituto Poligrafico e Zecca dello Stato, 1989), 80-81, 125-202.

1027

7 M. P. Alessandri, "II Restauro del Basamento di Michelangelo per Marco Aurelio", in Bolletino

Comunale dei Musei di Roma, VI (1992): 28-39.

8 De Monte, "Consolidanti e Protettivi".

9 Data Recording Forms compiled by D. Poggi for survey directed by M. Laurenzi Tabasso, from

Monument Treatment Forms supplied by Soprintendenza Archeologica di Roma; De Monte,

"Consolidanti e Protettivi".

10 De Monte, "Consolidanti e Protettivi".

11 Ibid; Monument Treatment Forms, Archive of Soprintendenza Archeologica di Roma.

12 Data Recording Form compiled by D. Poggi, from Monument Treatment Form, Archive of

Soprintendenza Archeologica di Roma.

13 M. Laurenzi Tabasso, M. P. Nugari, A.M. Pietrini, and U. Santamaria, "Sperimentazione per la Scelta

di un Protettivo da Applicare ai Materiali Costitutivi", in Fontana di Trevi, La Storia, II Restauro, ed. L.

Cardilli (Roma: Carte Segrete, 1991). 167-173.

14 G. Biscontin, E. Zendri, and A. Schionato, "Prottettivi Acrilici nella Conservazione della Pietra",

Materiali e Strutture. I. no. 3 (1991):95-110.

15 M. P. Alessandri, "II Restauro del Basamento," 37.

16 M. P. Alessandri, "The Arch of Titus in Rome: A Contribution for the Conservation of Surfaces" in

Proceedings of 7th International Congress on Deterioration and Conservation of Stone, Lisbon, 1992,

1455-1463.

17 L. Demitry. "The Conservation of the Stadium of Domitian in Rome", in Proceedings of the 6th

International Congress on Deterioration and Conservation of Stone, Torun, 1988, 748-756.

18 De Monte. "Consolidanti e Prottetivi". The lime wash mixture described here for the Stadium of

Domitian does not agree precisely with the above published report.

19 A. Melucco Vaccaro, Archeologia e Restauro (Milano: Mondadori, 1977), 255)

20 "Scheda relativa all'applicazione dello strato protettivo sulla superficie del capitello delta Colonna di

Foca". Unpublished treatment report of the conservation company, "Eleazar", 1986.

21 F. Piacenti, P. Tiano, C. Manganelli Del Fa, A. Scala, L. Medri, "Un Caso di Protezione del Marmo;

Controllo dell'Efficacia del Trattamento nel Tempo," in Atti del Convegno, 'Le Pietre nell'Architettura:

Struttura e Superficie', Bressanone, 1991, 797-803.

22 M. Laurenzi Tabasso and A. M. Mecchi, "Natural and Artificial Aging for Evaluating Waterproofing

Treatments for Marble" in Materiales de Construccion, 42, no. 226 (1992): 5-25.

23 M. Laurenzi Tabasso, et al., "Sperimentazione per la Scelta," 173.

24 Biscontin et al ., "Protettivi acrilici", 96-97.

25 M. Camaiti. R. lngoglia. G. Moggi, A Pasetti, A. Scala, "Controllo della Reversibilita di Trattamenti

Protettivi Effettuati con Polimeri Fluorurati su Materiali Lapidei", in Atti del Convegno, 'Le Pietre

nell'Architettura: Struttura e Superfici', Bressanone, 1991 , 267-276.

26 P. Tiano, M. Camaiti, P. Accolla, "Methods for the Evaluation of Products Against Algal Biocoenesis

of Monumental Fountains", in Preprints of International Colloquium. 'Methods of Evaluating Products for

the Conservation of Porous Building Materials in Monuments' Rome, 1995, 75-86.

27 E. Borrelli, M. Laurenzi Tabasso. M. Mariottini, L. Lazzarini, and D. Zanella, "The Arch of Alfonso of

Aragon in Naples, twenty years after a treatment with fluosilicates", in Supplement to Proceedings of 6th

International Congress on Deterioration and Conservation of Stone, Torun, 1988, 313-323.

28 AA. W., Doc. NORMAL 44/93, Procedimento per la misura in laboratorio e in situ della quantita

d'acqua che viene assorbita dal materiale a tempo definite, CNR-ICR, Roma, 1994

1028

29 R. Rossi-Manaresi, A. Rattazzi, L. Toniolo, "Long Term Effectiveness of Treatments of Sandstone",

in Preprints of International Colloquium, 'Methods of Evaluating Products for the Conservation of Porous

Building Materials in Monuments', Rome, 1995, 225-244.

30 AA. W., Doc. NORMAL 43/93, Misure colorimetriche strumentali di superfici apache, CNR-ICR,

Roma, 1994

31 Tabasso et al., "Sperimentazione per la Scelta", 169

32 U. Santamaria, "II Trattamento di Protezione delle Superfici in Travertine ed i Controlli SuccessM per

la Programmazione della Manutenzione" in S. Carlino alle Quattro Fontane, II Restauro della Facciata,

ed. N. M. Gammino, (Roma: CTR, 1993), 46-48.

33 AA. W., "Metodologia per la Valutazione di Prodotti lmpiegati come Protettivi per Materiale Lapideo"

in L'Edilizia, Nov., 1993, 57-71.

34 R. Rossi Manaresi, et al. "Long Term Effectiveness". 35 R. N. Butlin, T. J. S. Yates, and W . Martin, "Comparison of Traditional and Modern Treatments for

Conserving Stone" in Pre-prints of International Colloquium, "Methods of Evaluating Products for the

Conservation of Porous Building Materials in Monuments", Rome,1995, 111-120.

36 G. Torraca and P. Mora, "Fissativi per pitture murali", in Bolletino dell'lstituto Centrale del Res~auro

(1965): 109-132.

37 P. Mora, "Consolidamento Prowisorio di un Marmo in Stato di Avanzata Degradazione", in Atti del

Convegno lnternazionale di Studi, "La Conservazione delle Sculture all'Aperto, Bologna, 1969, 160-62.

The concentration of the Paraloid B72 solution used in this treatment was incorrectly reported as 15% in

G. Fazio, "Sull'Efficacia di Alcuni Trattamenti", 200.

38 Lazzarini, "Treatment Cards".

39 De Monte, "Consolidanti e Protettivi".

40 G. Accardo, R. Cassano, P. Rossi-Doria, P. Sammuri, M. Tabasso, "Screening of Products and

Methods for the Consolidation of Marble", in Proceedings of the International Symposium, 'The

Conservation of Stone', Bologna, 1981, 721-735.

41 A.E. Charola, M. Laurenzi Tabasso, U. Santamaria, "The Effect of Water on the Hydrophobic

Properties of an Acrylic Resin", in Preprints of Fifth International Congress on Deterioration and Conservation of Stone, Lausanne, 1985, 735-747.

42 De Monte, "Consolidanti e Protettivi".

43 Laurenzi Tabasso and Mecchi, "Natural and Artificial Ageing", 12, 18.

44 A.E. Charola, A. Tucci, R.J. Koestler, "On the Reversibilty of Treatments with Acrylic/Silicone Resin

Mixtures", in Journal of the American Institute for Conservation, 25 (1986): 83-92.

45 A. Tucci, R.J. Koestler, A.E. Charola, R. Rossi-Manaresi, "The Influence of Acid-Rain and UV

Radiation on the Ageing of Acrylic and Silicone Resins", in Proceedings of the Fifth International

Congress on Deterioration and Conservation of Stone, Lausanne, 1985, 891-898. 46 Biscontin, et al., "Protettivi Acrilici", 106-109.

47 R. Peruzzi, L. Toniolo, G. Alessandrini, "Protettivi e Consolidanti per Materiali Lapidei: Resistenza Fotochimica e Umidita Ambientale" Materiali e Strutture V, no. 1 (1995): 1-20. 48 Alessandri, "The Arch of Titus", 1460.

49 Biscontin, et al., "Protettivi Acrilici", 109.