Art conservation. Culture under analysis. I - ACS Publications

PART I

Art Conservation: Culture Under Analysis BEN B. JOHNSON and THOMAS CAIRNS Conservation Center, Los Angeles County Museum of A r t Los Angeles, Calif. 90036

CONSERVATION is a relatively new

disciphne which has attained maturity only in the last few decades. It evolved in the late 19th century through a synthesis of analytical science and restoration, which by the first decades of the 20th century bad developed into a new philosophy emphasizing respect of the material and aesthetic integrity of the original. Although there is no extensive history of restoration, there is evidence that man was concerned with preserving objects of both utilitarian and aesthetic interest several millennia before Christ. The Chou Chinese (1028-1256 B.C.) employed ingenious techniques in repairing their ceremonial bronzes. A Nishapur bowl (11th century A.D.) illustrates a crude type of ceramic repair utilizing bronze brackets to strengthen firing cracks or breaks (Figure 1). As early as the 16th century, accounts of restoration to paintings and sculpture indicate concern for restoring the original quality of the object. By the 18th century specialized techniques for treatment of objects had developed which were beyond the capabilities of the general artist or repairman. Transfer of paintings from original support to an entirely new one was practiced as early as 1741 by Frederic Dumesnil (1710-91) ( 1 ) . That Dumesnil had learned the technique from an Italian named Riario indicates it was already in use by the early 18th century in Italy. I n the early 19th century, transfer of paintings from panel support to canvas became a common practice as did frequent 24 A

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Figure 1. Ceramic plate, Nishapur, 11th century A.D. Metal brackets applied prior to burial indicate early repair technique

cleaning. However, the picture cleaning campaign initiated a t the National Gallery in London between 1846 and 1853 triggered the convergence of restoration and scientific analyses. Negative public reaction to the cleaned paintings prompted the House of Commons to form the Select Committee of Inquiry to investigate the National Gallery. The main purpose of this committee was to study the management of the National Gallery with special attention to its restoration practices. As a result, the committee published two reports which included interrogation of Gallery personnel and various experts covering such subjects as climatic conditions in the Gallery, cleaning practices, solvents, varnishes, relining and

ANALYTICAL CHEMISTRY, VOL. 44, NO. 1, JANUARY 1972

transfer procedures, and the formal training of restorers. The man mainly responsible for this cleaning campaign and Keeper of the National Gallery a t that time, Sir Charles Locke Eastlake, had published an important work on the technical history of paintings ( 2 ) . Thus, around 1850 the essential ingredients of Conservation had emerged: a study of the history of technology, awareness of environmental factors, examination of restoration practices and materials, and a concern for preventive and preservative methods. Throughout the latter half of the 19th century, interest in the problem of preserving and restoring art ohiects steadily increased. Berger and Eihner in Germany, Russel and Abney ( 3 ) in England, plus many

REPORT FOR ANALYTICAL CHEMISTS

Art conservation is a new discipline which utilizes modern analytical chemical techniques in the study and preservation of unique objects of artistic and cultural importance. Today’s public consciousness of cultural heritage has elevated conservation to a new significance in the museum world

others concerned themselves with understanding not only the materials employed but also the effect of environmental agents on these materials. I n this century knowledge bas rapidly increased, and new materials and technology exist which are continually being evaluated by conservators for their potential application to the preservation of art objects. I n the United States, first a t the Boston Museum of Fine Arts in 1928 and then a t the Fogg Art Museum in 1932, scientific laboratories devoted solely to the study of art objects were established. I n the last 30 years many conservation laboratories have been established -Le., Instituto del Restauro, Rome; Institut Royal du Patrimoine Artistique, Brussels; and the Los Angeles County Museum of Art in January 1967. Conservation can be defined as the application of science to the examination and treatment of objects of art and to the study of the environments in which they are placed. Art restoration is that portion of conservation which deals primarily with the treatment of objects. It should be understood that restoration does not imply an attempt to return the object to its original state hut rather to prevent deterioration of the original materials while respecting their integrity.

jor elements which concern the museum conservator. The effects of light on art objects have been studied since the late 19th centurnfirst by George Field who studied the fading and darkening of pigments and then RlcIntyre and Buckley who noted the effect of humidity on the rate of fading. More recent studies have revealed that short wave ultraviolet in daylight and fluorescent lighting is the most dangerous to museum objects ( 4 ) . By far the most susceptible objpcts

to fading are textiles, wat,ercolors, pastels, inks, and colored prints which often have organic pigments and dyes subject to photodecomposition. A similar phenomenon can also occur in oil or tempera paintings when a fugitive pigment is present,, although the prot,ection afforded by the oil medium will reduce the overall kinetic rate of such processes (Figure 2 ) . Cellulosic materials, especially papers and textiles, undergo degradation such as discolor-

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Figure 2. Detail, figure of standing saint by Antonio Crivelli. Italian. 15th century Dotted line shows area protected by frame. To right of line. deep red color of garment has been preserved. T O left. faded color reveals underdrawing

Environment and A l t Object

Environment, as related to the art object, is defined as the aggregate of all the external influences on the object. Light, humidity, and atmospheric pollution are the three maANALYTICAL CHEMISTRY, VOL. 44, NO. 1, JANUARY 1972

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Report for Analytical Chemists Active Bronze

CU*(OH)&I Pale Green

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Figure 3. Schematic drawing of patination layers on ancient bronze shows active bronze disease

ing or tendering on exposure to ultraviolet light. Such harmful effects through exposure to strong ultraviolet light can be reduced considerably liy the use of screening agents. Plexiglas is commonly employed as glazing in picture frames since it contains ultraviolet absorbers. Various plastic coatings containing absorbent materials are available to coat windows and skylights, and ultraviolet abcorbing

sleeves are manufactured to slip over fluorescent tubes ( 4 ) . The control of relative humidity in the museum is of tremendous importance because it directly influences the dimensional stability of certain materials. Objects may also develop fungi, efAoresce salts, or ot 11ern. i sc de t e ri o r a t e i f strict humidity control i, not maintained. The lower limits of relative humitlity arc dictated by objects cuch ab panel painting- and furniture which 1i:ire complicated n-ood itructures and which respond dirnensionally to humidity changes. h relative humidity below 50% may cause paint to flake, furniture and wooden sculpture t o develop cracks, and Oriental scrolls to curl. On the other hand, relative humidities above 65% can foster mold growth in paper, canvas, and textiles. For these rcacons, museums attempt to maintain a relative humidity a t some point hetween 60-65% at a temperature hetween 68-72 OF. Often intlividual ohjects require .pecial attention with respect to relative humidity hccausc of their chemical make-up or h c c a i i ~ eof uniisual structiiral problems. For example, bronzes buried for a long time acquire a protective coating or corrorion layer consisting usually of b a si c copper c ar bona t e ini a la ch it e ’l

and cuprous oxide (cuprite). Sometimes a thin layer of cuprous chloride is also present (Figure 3 ) . Loss of the overlying malachite and cuprite accelerates the conversion of this cuprous chloride to cupric chloride-a light green powdery deposit (Figure 4 ) . This so called “bronze disease” eats away at the bronze unless arrested by treating or by maintaining a low relative humidity. Yet another unusual problem arose when Rembrandt’s famous “Self-Portrait” of 1638 (see cover) was purchased in London about two ycars ago and brought to Los Angeles. Although the Los Angeles County lluseum of Art has well controlled relative humidity a t 52% (t4%), the painting had adjusted to the damper conditions in Great Britain. The panel on which the self-portrait is painted is a complex structure which when slightly warped has tremendous stress imposed upon it by the distortion of the horizontal elements a t the top find hottom, much the same as a bow drawn back under tension. By experimentation in an environmental chamber, the panel, warped badly at 62% RH (museum conditions). was totally relaxed at 60 2 2% relative humidity (Figure 5 ) . h plexiglas case designed to fit into the ornate Louis SIV antique frame was filled vith silica gel previously conditioned in a chamber to 60% RH and sealed with the painting inside (Figure 6 ) . The special case with appropriate hygrometer and thermometers visible on the reverse maintains the internal humidity required to relieve tension within the panel support. From the normal front view, the painting appears siin1)Iy as if glazed for protection againat light and dust (Figure 7 ) . Atmospheric pollutantrs are somen-hat more complex and difficult to overcome than light and humidity. I n the urban atmosphere such as LOThngeles, sulfur dioxide. hydro60% RH

Figure 4. Syro-Hittite bronze figure, 2nd millennium B.C. Arrow points to outcropping of “bronze disease”

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52% RH

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Figure 5. Relative position of oak panel support for Rembrandt‘s “Self-Portrait,” Norton Simon Foundation Collection, a t 5 2 % relative humidity and a t 60% Panel is in relaxed state


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gen sulfide, and ozone can cause rapid defacement of works of art,. Examination of Objects of Art

When an ohject enters the Conservation Laboratory, it undergoes an examination to determine its state of preservation. Information on the original materials and struct,urc, former restorations, and deterioration is collected and used in determining the best technique for preserving the original. Of equal importance, the examination fulfills t,he purely academic function of providing knowledge of earlier cnltures anrl technology. The conservator, curator, or collector often suffers the embarrassment of not knowing how to answer the Iaymen's simplest questions, "What is it made of? How was it done?" Through documentat,ion and analysis, the conservator is only recently

Figure 7.

Rernbrandt's "Self-Portrait" a s It appears an exhibit

Humidity Control case aids in preservation O f painting. yet does not impede Viewer's enjoyment of the great masterpiece

beginning to provide a few of t,he hasic answers on technology and materials of earlier cultures. The examination of an art, object generally hegins with a simple visual inspect,ion hy use of special lighting to cnable the conservator's trained differ. . . . . . . I _PVP t,n .- distinguish , ences in color, Igloss, texture, or other material iriregularities which may indicate p o l :dems in the strncture. Based on ithc results of the initial ohservatiaIns, photographic techniques are u sed to document "..,I C..",l.^" -i..-1-. L I L L L ~ ~ U L L I I T Ib ~ r t y the condition of the object. Raking light photographs (a strong light is placed a t a n oblique angle to the surface) show irregularities or deterioration in the structure because of the emphasis on surface relief. When a strong photo light is placed hehind t,he painting, light transmitted through the canvas and paint struc-i-

ture can show old damages and losses and occasionally give a clue to the painting tcehnique (Figure 8 ) . Examination by ultraviolet light sometimes enables differcntiation hetwen the restored anrl original materials bccanse of a difference in fluorescence. The fluorescence of some pigments and varnishes proqides inforinat,ion d i i c h may be important during t,reat,ment of the painting. Infrared photographs can reveal damages or a preliminary drawing ( 5 ) nndcr layers of dark varnish or bronnish paint vhidi may be transparent to invisible infrared. Recently, color infrared photographs havc been nsed by t,he authors t o identify various pigment,s, both organic and inorganic, on Indian miniature paint,ings dating from the 10th through the 19th cent,uries (6). X-rays (first applied to paintings


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Report for Analytical Chemists

in the paint structure. White lead is usually more abundant and thicker than most pigments, but "them siirh m n- , - ...-.I - - .. R S vermillion . ......._ .. 1HorS) ~--~ also be recorded on the X-ray film. I n addition, old repairs and retouchings seldom have the same densities as the original paint and are detectable in radiographs. Rembrandt, Van Gogh, and other artists made frequent compositional changes which when studied in radiographs give insight into the understanding of the artist's technique (Figure 9 ) . Radiographs are extremely useful for three-dimensional objects where inner structures, joints, cores, etc., can be seen (Figure 10). Neutron radiographs have proved useful for studying the organic matter trapped in metal objects, specifically the core material in ancient bronzes which contains carbon (Figure 11). The stereobinocular microscope, which magnifies np to about 40X, is used to make more exacting observations on paintings. One can distinguish retouching from original paint, age cracks, individual pigment particles, brushwork, etc. Dnring treatment the stereomicroscope is used for taking minute samI

Figure 8. Transmitted light photograph of early American painting is used t o document hundreds of small losses of paint

by R6eLlLsGlL Call I c i y c a l old damages and artist's changes and may help in the study of the strncture of the painting. Since the major white pigment used in European easel paint,ing unt,il the early 19th century was lead white (PbCO,), exposure to X-rays results in a film record of densities

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ples (less than a milligram) which can be used for analysis hy wet chemical methods utilizing the comnmmd miomsonno niimemiip. __..___I r _ iinrlpr _.._"_ __"_" types of light conditions-Le., polarized, fluorescent, transmitted. Cross sections of paint structures studied under 100-200x magnification show clearly the stratography of the painting-Le., how it was built up from the support and of what pigments the layers are composed. For example, a rich luminous maroon from a 15th century Flemish painting may owe its beauty to a n underlayer of fiery vermillion. Cross sections of ceramics, bronzes, and even papers give extremely valuable information in determination of what treatment should be applied. Although every conservation laboratory relies heavily on traditional analytical methods, most have specialized in some area of instrumental analysis. More and more, conservation chemists are tackling specific research problems, either organic-Le., media, varnishes, dyes and adhesives-or inorganic pigments, metals, ceramics, and stones. Because of space limitations, it is possible to mention only a few of I "

Figure 9. Left, "L'Hiver" by Van Gogh, Norton Simon Foundation Collection. Normal photograph and radiograph (30 kV, 5 mA. 1 min, 30-in. distance). Right, Van Gogh used one of his earlier canvases of a "Woman Spinning" t o paint winter scene Radiograph is EO clear was used

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because first painting wa's done with lead white pigment. whereas in top Of winter scene, zinc white. a less dense pigment.

ANALYTICAL CHEMISTRY, VOL. 44, NO. 1. JANUARY 1972


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Figure 10. Left, normal photograph and right, radiograph of bronze “Buddha,” Gupta period, ca. 6th century, Indian. Los Angeles County Museum of Art Radiograph (250 kV. 6 mA. 10 min. 404”. distance) shows modern repair in lefl leg proper. White dense areas are part of internal sprue System used in Casting hollow bronze

the instrumental analytical techniques which have proved most useful. The work of Stolow, utilizing the technique of gas chromatography to separate linseed oil components, has been most rewarding ( 7 ) . Essentially, the triglycerides of three of the basic fatty acids (oleic, linolenic, and linoleic) in linseed oil are converted by the process of transesterification into methyl ester molecules volatile enough to he separated on a gas chromatographic column. Not only has Stolow’s work been most enlightening in understanding the essential processes involved in drying of linseed oil, hut with further work it may prove useful in the study of modern paintings of doubtful authenticity. Stolow’s earlier research on the effects of various solvents on linseed oil films has contributed greatly to the evaluation of picture cleaning processes. Although used to identify media and adhesives, infrared spectroscopy has proved most useful in studies of varnishes used as surface coatings on paintings (8). I n addition to fundamental research on media and adhesives, the identifica-

tion of varnish type films often becomes essential to practical problems in cleaning. Robert Feller of the Mellon Institute has done invaluable work on varnish materials and has defined their physical as well as chemical properties. H e has led a campaign to develop the perfect picture varnish (9). Modern plastics such as acrylics and vinyl acetates have proved to be tough and enduring replacements for the traditional mastic and damar resins which discolor and embrittle badly with age. Recently, work has been carried out a t the Los Angeles County Museum of Art with the MS902 mass spectrometer for analysis of media in Indian miniature paintings (Figure 12). The medium, usually an exudate from a tree such as gum arabic, is first hydrolyzed into its basic components-i.e., galactose, arabinose, mannose. A refinement of the chromatographic technique as described by Mme. Flieder (IO) enables identification of the various gums. Individual components are further studied through mass spectrometric analysi,s. The next

phase of study on the Indian miniature research a t the Conservation Center is the identification of organic pigments. More progress has been made in the field of inorganic analysis, partly because any organic materials introduced during modern treatment do not confuse the issue and partly because of the statistical abundance of metal and ceramic objects from important ancient cultures. Gettens a t the Freer Gallery of Art has pioneered the study of ancient Chinese bronzes (II ) . His definitive work combines wet chemistry and emission spectrometric analyses t o determine major, minor, and trace elements of bronze ceremonial vessels. Metallographic studies on etched sections and microscopic surface studies along with radiographs and X-ray diffraction analysis have enabled Gettens t o determine composition, fabrication methods, surface decoration techniques, and patination types. The monumental nature and classical quality of Getten’s research have established the standard for future research on art technology.

Neutron radiograph courtesy Narth American Rochweil

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Fieure 11. Neutron radioeraoh of Chin&e bronze ceremonial vessel, “Ting,” Chou dynasty Note clay core in leg


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since it combines the sampling and analysis in a single stage. The increasing importance of analysis in evaluation, authentication, and treatment has prompted the conservator to rely heavily on new, sensitive techniques and to refine sampling and sample handling EO that he can deal with extremely small specimens. The techniques briefly reviewed in the foregoing paragraphs are hut a few of the many promising analytical techniques in current use (16). Treatment of Art Objects

The most difficult and demanding task facing the Conservator is the treatment of an art object. It is impossible to discuss here all types ^e

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Figure 12. MS902 mass specti'ometer at Los Angeles County Museum of Art, Conservation Center Instrument was gift

Of

Mr. and Mrs. Iitanton Avely

X-ray diffraction techniqut ?shave become important for pigmen t studies not only because of their sensitivity but also because of the differentiation of crystal structure ( l a ) . This is important when dealing with materials chemically similar hut ith different crystal designs-i.e., zurite vs. malachite or chrysocolla. omhined with emission spectrograhy or mass spectrometry, this proides a thorough and accurate nalysis. Inorganic mass spectrometry has :en successfully applied to art ohcts, especially for metals and pigtent analysis ( I S ) . Currently, the os Angeles County Museum of Art using mass spectrometry to .udy a large group of Luristan ronzes approximately 3000 years d. The small sample size (milli,:am range) and the sensitivity to trace elements provide potential for studies on geological sources for materials of art. This avenue of study has previously scarcely been considered because of the large quantity of material required to ohtain accurate trace analysis with other techniques. Mass spectrometry has also been applied to pigment studies (European easel paintings, Indian miniatures, etc.) ; currently, a complete oollection of pigments (Forbes Collection) provided by the Conservation Center of New 30 A

York University is being fingerprinted in Los Angeles. n necenuy, nxr- r a y nuorescence na8 been used a t the Winterthur Museum by Hanson for studies of silver objects. The technique is extremely useful as it is not necessary to remove a sample of the object but simply to focus on a surface zone. He has so far been able to establish differences in British sterling and American silver of contemporaneous dates. William Young at the Conservation Laboratory of the Boston Museum of Fine Arts has applied the laser microprobe to the analysis of art objects with great success (14). Advantages of this technique are its removal of a sample only ahout 50-80 p in diameter and the easy analysis of nonmetallic objects. It is also extremely useful on paintings 7 .

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undergo, e,ach of which may require a {treatment process if preservation i;s to he ensured. Art obiects are iindividuals by their very definition, and each must he studied to determi[ne its makeup and properties. Orily after a thorough study ana mucn testing can the proper treatment he developed. The treatment of paintings requires considerable experience and knowledge of painting techniques. The nature of the painting support, whether canvas, panel, metal, glass, paper, or other, will greatly influence the decision as to what should be done to preserve it (Figure 13). On the support is a rather complex structure of ground and design layers. These may he any one of numerous types of p a i n t i . e . , oil, egg tempera, glair (white of egg), watercolor (gum arabic), distemper (animal glue), or a synthetic resin (acrylic or vinyl). Often the ground layer is one type of medium -Le., glue with drying oil or egg tempera on top. T o further com-

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I I Figure 13. Schematic drawing of structure of early Italian painting shows complex structure from panel support to surface coating


Figure 14. ”Por. trait of Viscount Barrington“ by Gil. bert Stuart, American, late 18th-early 19th century, Los Angeles County Museum ofArt Painting io shown during cleaning pro. cess with varnish removed from left side

ciianed area

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Catalog 1971-72 \

plicate the matter, a surface coating is usually present of natural soft resin (damar, mastic), wax, glue, natural hard resin (copal, amber), or synthetic resin (acrylic, vinyl). Not only are we faced with a complex structure of materials with vastly different chemical and physical properties, but the technical idiosyncrasies of each artist must he considered. Perhaps the most complex process is safe removal of varnish and retouching from old master paintings. Varnish removal from an oil painting has both physical and aesthetic value. A vast majority of oil paintings or egg tempera paintings were covered with soft resin varnishes sometime within the last century and a half. Although virgin surfaces which predate the 19th cent u r y are rare, they are encountered occasionally. Soft resin varnishes not only discolor badly, hut they also embrittle and crack with age and lose their protective value. The “Portrait of Viscount Barrington” by Gilbert Stuart (Figure 14) illustrates the detrimental effects of varnish on the color qualities of the painting. I n this case, the painting was covered with a soft resin varnish which contained a small percentage of drying oil. Acetone diluted with naphtha

proved effective in removing the varnish film without disturbing the original oil medium. Since the linseed oil polymers in the paint medium cross-link with age, they hecome more and more resistant to the solvents necessary for removal of natural resin varnishes. Certain periods in the history of painting present problems in cleaning-Le., early English paintings hy artists such as Reynolds, Morland, and Constable often contain oleo-resinous media which have such a high resin content that normal crosslinking of the oil does not occur. The problem of removing varnish from oil-resin films can usually he solved by utilization of a technique called “reforming” ( 9 ) . The surface film is sprayed with a slow evaporating solvent mixture and left for a period ranging from a few hours to a week. The reformation of the varnish in this manner makes it soluble in much milder solvents, such as toluene, which generally do not affect a n oil-resin film. It is believed that the swelling caused by the initial spray solvent mixture breaks secondary linkages in the resin molecules which would require months to he reestablished. Two other examples will illustrate more complex problems where large areas of the original surface have

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Figure 15.

“A Sibyl’’ by Jusepe de Ribera. Spanish, 17th century. San Diego Museum of Fine Arts

Left, before treatment; center. radiograph (30 Kv. 5 mA, 1 min. 304”. distance) Of lower left portion shows child’s head under visible Surface: right. after treatment

Figure 16. “The Martyrdom of Pope Caius” by Lorenzo Monaco, Italian. 15th century, Santa Barbara Museum of A r t Lett, before treatment right, after treatment

been repainted by an early restorer to the extent that the composition and quality of the original design have been altered. A painting by Jusepe de Ribera, a 17th century Spanish painter, representing an old woman gesturing with her right hand and entitled “A Sibyl” (Figure 1 5 ) , came t o the laboratory for examination. Radiographs of the lower left quadrant revealed a child’s head under the visible surface. Ultraviolet examination indi32 A

cated gross overpainting in the same area. Solvent tests were made on the retouched area, and dimethyl sulfoxide used in conjunction with acetone was applied to dissolve the repaint, whi.ch was oil, hut had a different solubility from the original. The child’s figure was uncovered in good condition, and the original composition regained. Of course the picture must now he restudied by art historians t o correctly identify the subject matter.

ANALYTICAL CHEMISTRY, VOL. 44, NO. 1. JANUARY 1972

The second example is an egg tempera painting on poplar panel hy Lorenzo Monaco representing “The Martyrdom of Pope Caius” (Figure 16). The gold background in the upper left portion and the gold decoration on the garments of the figures, as well as the helmets and gloves of the figures in armor, have been repainted by a restorer. The gold retouching could not he recorded by using photographic techniques, hut. a cross section made

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Figure 17. “Anatolian Bull.“ Boston Museum of Fine Arts Left. before treatment: right. after electrolytic treatment. Note especially well-preserved silver surface

from a sample taken in the gold area clearly revealed two layers: the thick gold leaf and the thinner modern gold paint. After removal of the gold repaint, the original surface was in unusually good condition. I n the armor the areas which had been overpainted a dark blue color show traces of silver leaf which would have given a rich metallic luster in contrast with the surrounding gold. Structural work on paintings often requires lining of the original canvas, or on panels, applications of moisture barriers, or sometimes transfer of the original t o a new support. Lining is generally carried out on a vacuum hot table which utilizes atmospheric pressure to hold the original canvas in contact with the lining canvas while a thermoplastic material adheres the two together. Lining adhesives require more research. Traditional waxes or mixtures of waxes, resins, and balsams have been used. These adhesives have been favored because the process is reversible simply by reheating, and they also provide a certain amount of protection from humidity changes. Modern synthetic waxes or mixtures will probably yield a more neutral and durable product once enough research is done by conservators on their aging properties. Cleaning of metals is another exacting process since their natural patinas, usually carbonates or oxides of copper on bronzes, often must be preserved. Surface dirt and resinous accretion from an Indian bronze was removed mechanically with brushes and scalpels without affecting the green malachite surface. The base of the bronze which had a heavy accretion 34A

was first, bombarded with ultras onic waves nrhile in a detergent bat h t o . . .. ...L., .,:-A 1 ._.._ soften the ImpacLeu uirli layer ;then it could he easily removed. If it is necessary to convert or rem”move the patina in a cleanink” plucess, electrolysis can be employed. The Anatolian bull (Figure 17) shows the effectiveness of electrolysis in revealing a silver surface. The piece was first wound with copper wire and then hung as a cathode in a bath with an electrolyte of 2% sodium hydroxide. Iron annodes were hung on either side of the bull, and a 0.5 ampere current was applied. The electrolytic reduction took about five days with washing and brushing after three days. Small areas of “bronze disease” (see Figure 2) can be treated by excavation of the area and packing with silver oxide. The silver oxide combines with the copper chlorides to form silver chloride which is insoluble and will stop further deterioration. Where entire objects require treatment for “bronze disease,” they can he soaked in a solution of sodium sesqui carbonate ( 5 % ) . The piece is washed frequently until chlorides can no longer he detected in the wash water. Graphic arts such as prints and drawings have often been damaged owing to negligence and poor framing practices. Pulpwood cardboard, extremely acidic (pH ~ i :4.51, was for many years the most popular type of mounting and matting material. Of course, the acidic property of the surrounding materials migrates into the original paper and causes embrittlement and discoloration. Unlike easel paintings where damage to support does not always mar the design itself, the paper is usually an integral part of the

ANALYTICAL( :HEMISTRY. VOL. 44. NO, 1, JANUARY 1972

graphic expression, and deterioration can cause a loss in quality. I n addition to removal of the acidic materials and replacing them with chemically neutral matt boards, the original paper often requires bleaching (16) to remove stains and discoloration, and deacidification to prevent further deterioration. Deacidification is accomplished by application of a magnesium bicarbonate to the paper to neutralize the PH ( 1 7 ) . I n next month’s issue the authors will discuss some of the more significant conservation research projects and techniques of analysis. References

(1) D. Coekelhergs, “Precisions sur la vie et L’oeuvrc du Peintre-Restaurateur Bruxellois FrPderic Dumesnil (vers 1710-91.” Bulletin, , lnstitut Royal du Patrimoine Artistique, Brussels, Beleium. 11. 174 (1969).

(3) E. Berger, “Beitrage zur Entwickelungs-Geshiehte der Maltechnik,” 4 vol, Munich, Germany, 19013; A. Eibner, Entwickelung und Werkstoffe der Wandmalerei,” Munich, Heller, 1926: IT,J. Russel and W.L. Abney, “Report to the Science and Art Department of the Committee of the Council of Education on the Action of Light on Watercolors,” H.M. Stationary Office, London, England, 1888. (4) R. L. Feller, “Control of the Deteriorating Effects of Light upon Museum Objects,” Museum, XVII (2) (1964). ( 5 ) J. R. J. Van Asperen de Bier, “Infrared Reflectography-A Contribution to the Examination of Earlier European Paintings,” J. F. Duwaer, Amsterdam, Holland, 1970. (6) B. B. Johnson, “The Technique of Indian Miniature Paintings,” Los Angeles County Museum of Art Symposium on Indian Art, to he published, 1971. (7) N. Stolow, “The Application of Gas Chromatography in the Investieation of Works of Art,” in “Application of Science in Examination of Works of


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Art,” Boston Museum of Fine Arts, Boston, Mass., 1967, pp 172-83. (8) R. Kleber and F. TricabMarckx, “Identification d’une Vernis Moderne Rccouvrant la Decente de Croix de Ruhens,” Bulktin, Institut Royal du Patrlmoine Artistique, Brussels, Beleium. 6.G3 (1963). ~, (9) R. Feller, N. Stolow, and E. Jones, “On Picture Varnishes and Their Solvents,” rev. ed., Case Western Reserve Universitv. Cleveland. Ohio. 1971. (10) F. Fleider, Stud. ‘Conseru., 13, 49 (196X). .~ .., (11) R. J. Gettens, “Freer Chinese Bronses, Vol 11, Tech. Studies,” Smithsonian Inst., Washington, D.C., 1969. (12) H. Barker, “Spectrographic and Xray Diffraction Methods in the Museum Laboratory,” m “Application of Science in the Examination of Works of Art,” Boston Museum of Fine Arts, Boston, Mass., 1967, pp 218-21. (13) T . Cairns, “Spark Source Mass SpecI

trometry,” IIC-AG Technical Papers 1968-70, Conservation Center, NYU; New York, N.Y., 1970, pp 47-58. (14) W. Young, “The Laser MicroDrobe

I

ton; Mass., 1967, p 230. (15) For further reading, see “Studies,in Conservation,” Aberdeen University Press. Aberdeen. Scotland. Duhlished quarterly, 195giresent; abo; “Recent Advances in Conservation,” G . Thompson, Ed., Butterworths, London, England, 1963. (16) For various bleaches, see H. J. Plenderleith, “The Conservation of Antiquities and Works of Art,” Oxford University Press, London, England, 1956. (17) W. J. Barrow, Spray Deacidification Permanence/Durability of the Book 111, W. J. Barrow Research Laboratory, Richmond, Va., 1964.

Conservation,” several articles on conservation, and at the moment has two definztive articles in press, “Technique of Indian Miniature Paintings,” and “South Indzan Bronzes.” P‘

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Ben B. Johnson, Head of the Conservation Center, Los Angeles County Museum of Art, received his B A in mathematics at the College of William and Mary and his M A in art history at the Institute of Fine Arts, NYU. He received the Certificate in Art Conservation from the Conservation Center of NYU. I n Italy he studied at the U f i z z i with Lionetto Tintori and later received a Diploma in Art Conservation from Ghent University. In 1964 he became Conservator of European Paintings at the Freer Gallery of Art, Smithsonian Institution. I n 1967 he established the Conservation Center of the Los Angeles County Museum of Art and was appointed Lecturer in Art Conservation in the Graduate Art History Department at UCLA. A Fellow of the Institute for the Conservation of Antiquities and Works of Art and a Consultant Fellow of the Conservation Center, Institute of Fine Arts, N Y U , he has lectured widely in museums on the West Coast. He has published a small book entitled “Introduction to Art

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ANALYTICAL CHEMISTRY, VOL. 44,NO. 1, JANUARY 1972

Cairns, Conservation Chemzst for the Los Angeles County M u s m m of Art, received his PhD degree in chemical spectroscopy from the Unwersity of Glasgow, Scotland, in 1965. He joined Heyden and Son, Ltd., as publishing director in 1965 and served in this capacity until his appointment at the Museum in J u n e 1968. Dr. Cairns was editor and author of the series, “Spectroscopy in Education,” Heyden, 1967, and is the author of numerous papers dealing with hydrogen bonding in natural products. He was a summer session lecturer in chemistry at UCLA, 1968-71, and is a sciemce advisor to the Food and Drug Administration in Los Angeles. Currently, Dr. Cairns ZS engaged in the application of mass spectrometry in an attempt to establish the origin of art objects via their trace analysis. Thomas

Art conservation. Culture under analysis. I - ACS Publications

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