Art Conservation: Culture Under Analysis - Analytical Chemistry (ACS

PART I

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

is a relatively new discipline which has attained m a t u r i t y only in the last few decades. I t evolved in the late 19th century through a synthesis of analytical science and restoration, which by the first decades of the 20th century had 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 t h a t man was concerned with preserving objects of both utilitarian and aesthetic interest several millennia before Christ. T h e 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. CONSERVATION

B y 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). T h a t Dumesnil had learned the technique from an I t a l ian named Riario indicates it was already in use by the early 18th century in Italy. In 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 at 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. T h e 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

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transfer procedures, and the formal training of restorers. The man mainly responsible for this cleaning campaign and Keeper of the N a tional Gallery at t h a t 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 objects steadily increased. Berger and Eibner 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 m a t e rials employed but also the effect of environmental agents on these m a terials. I n this century knowledge has rapidly increased, and new m a terials and technology exist which are continually being evaluated by conservators for their potential a p plication to the preservation of art objects. In the United States, first at 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 m a n y conservation laboratories have been established —i.e., Instituto del Restauro, Rome ; Institut Royal du Patrimoine Artistique, Brussels ; and the Los Angeles County Museum of Art in J a n u a r y 1967. Conservation can be denned as the application of science to the examination and treatment of objects of art and t o the study of the environments in which they a r e placed. Art restoration is t h a t portion of conservation which deals primarily with the treatment of objects. I t should be understood t h a t restoration does not imply a n a t tempt t o return the object t o its original state but rather to prevent deterioration of the original m a t e rials 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 century— first by George Field who studied the fading and darkening of pigments a n d then M c l n t y r e and Buckley who noted the effect of humidity on the rate of fading. More recent studies have revealed t h a t short wave ultraviolet in daylight and fluorescent lighting is the most dangerous t o museum objects (4) • By far the most susceptible objects

to fading are textiles, watercolors, pastels, inks, a n d 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 protection 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-

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. To left, faded color reveals underdrawing

Environment and Art Object

Environment, as related to the a r t object, is defined as the aggregate of all the external influences on the object. Light, humidity, and a t m o spheric pollution are the three m a ANALYTICAL CHEMISTRY, VOL. 4 4 , NO. 1, JANUARY 1972

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Report for Analytical Chemists

Paratacamite

Active Bronze Disease ^V,

Cu2(OH)3CI Pale Green

i

CuCO y Cu(OH) 2 Green

H20

+

02

Cu 2 0 - Red

Nantokite

CuCI - Grayish

Cu:Sn:Pb

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 by 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 absorbing

sleeves are manufactured to slip over fluorescent tubes (4) • T h e 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, effloresce salts, or otherwise deteriorate if strict humidity control is not maintained. T h e lower limits of relative humidity arc dictated by objects such as panel paintings and furniture which have complicated wood structures and which respond dimensionally to humidity changes. A relative humidity below 5 0 % may cause paint to flake, furniture and wooden sculpture to develop cracks, and Oriental scrolls to curl. On the other hand, relative humidities above 6 5 % can foster mold growth in paper, canvas, and textiles. For these reasons, museums a t t e m p t to maintain a relative humidity a t some point between 50—65% a t a temperature between 68-72 ° F . Often individual objects require special attention with respect to relative humidity because of their chemical m a k e - u p or because of unusual structural problems. For example, bronzes buried for a long time acquire a protective coating or corrosion layer consisting usually of basic copper carbonate (malachite)

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 b y 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 years ago and brought to Los Angeles. Although the Los Angeles County Museum of Art has well controlled relative humidity at 5 2 % ( ± 4 % ) , the painting had adjusted to the damper conditions in Great Britain. T h e 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 at the top and bottom, much the same as a bow- drawn back under tension. By experimentation in an environmental chamber, the panel, warped badly at 5 2 % R H (museum conditions) , was totally relaxed a t 60 ± 2 % relative humidity (Figure 5 ) . A plexiglas case designed to fit into the ornate Louis X I V antique frame was filled with silica gel previously conditioned in a chamber to 6 0 % R H and scaled with the painting inside (Figure 6 ) . T h e special case with appropriate hygrometer and thermometers visible on the reverse maintains the internal humidity required to relieve tension within the panel support. F r o m the normal front view, the painting appears simply as if glazed for protection against light and dust (Figure 7 ) . Atmospheric pollutants are somewhat more complex and difficult to overcome t h a n light and humidity. In the urban atmosphere such as Los Angeles, sulfur dioxide, h y d r o 60% RH

1 1/4" 52% RH Figure 4. Syro-Hittite 2nd millennium B.C.

bronze figure,

Arrow points to outcropping of "bronze disease"

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Figure 5. Relative position of oak panel support for Rembrandt's "Self-Portrait,' Norton Simon Foundation Collection, at 5 2 % relative humidity and at 6 0 % Panel is in relaxed state

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


Figure 6. assembly

H u m i d i t y c o n t r o l case d u r i n g

Painted panel (in small padded frame) is facedown in plexiglas case; silica gel framework inserts over panel back; neoprene t u b i n g rests in groove visible on upper edge of framework, back plexiglas cover

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

When an object enters the Conservation Laboratory, it undergoes an examination to determine its state of preservation. Information on t h e original materials and structure, former restorations, and deterioration is collected and used in determining the best technique for preserving t h e original. Of equal importance, the examination fulfills the purely academic function of providing knowledge of earlier cultures and technology. T h e conservator, curator, or collector often suffers the embarrassment of not knowing how to answer the laymen's simplest questions, " W h a t is it made of? H o w was it done?" Through documentation and analysis, t h e conservator is only recently

Figure 7.

R e m b r a n d t ' s " S e l f - P o r t r a i t " as it appears on e x h i b i t

Humidity control case aids in preservation of painting, yet does not impede viewer's enjoyment of the great masterpiece

beginning to provide a few of the basic answers on technology and materials of earlier cultures. The examination of an art object generally begins with a simple visual inspection by use of special lighting to enable the conservator's trained eye to distinguish differences in color, gloss, texture, or other material irregularities which m a y indicate problems in t h e structure. Based on the results of the initial observations, photographic techniques are used to document and further study t h e condition of the object. R a k i n g light photographs (a strong light is placed at an 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 behind the painting, light transmitted through the canvas and paint struc-

ture can show old damages and losses and occasionally give a clue to the painting technique (Figure 8). Examination by ultraviolet light sometimes enables differentiation between the restored and original materials because of a difference in fluorescence. T h e fluorescence of some pigments and varnishes provides information which m a y be important during treatment of the painting. Infrared photographs can reveal damages or a preliminary drawing (5) under layers of dark varnish or brownish paint which m a y be transparent to invisible infrared. R e cently, color infrared photographs have been used by the authors to identify various pigments, both organic and inorganic, on Indian miniature paintings dating from the 10th through the 19th centuries (6). X - r a y s (first applied to paintings

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Figure 8. Transmitted light photograph of early American painting is used to d o c u m e n t hundreds of small losses of paint

by Roentgen and Curie) can reveal old damages and artist's changes and may help in the study of the structure of the painting. Since the major white pigment used in European easel painting un til the early 19th century was lead white ( P b C 0 3 ) , exposure to X - r a y s results in a film record of densities

in the paint structure. White lead is usually more a b u n d a n t and thicker t h a n most pigments, but others such as vermillion (HgS) can also be recorded on the X - r a y film. In addition, old repairs and retouch ings seldom have the same densities as the original paint and are de tectable in radiographs. Rem brandt, Van Gogh, and other art ists made frequent compositional changes which when studied in ra diographs give insight into the un derstanding of the artist's technique (Figure 9 ) . Radiographs are ex tremely useful for three-dimen sional objects where inner struc tures, joints, cores, etc., can be seen (Figure 10). Neutron radiographs have proved useful for studying the organic m a t t e r trapped in metal ob jects, specifically the core material in ancient bronzes which contains carbon (Figure 11). The stereobinocular microscope, which magnifies up to about 4 0 X , is used to make more exacting obser vations on paintings. One can dis tinguish retouching from original paint, age cracks, individual pig ment particles, brushwork, etc. During treatment the stereomicroscope is used for taking minute sam

ples (less than a milligram) which can be used for analysis by wet chemical methods utilizing the com pound microscope under numerous types of light conditions—i.e., po larized, fluorescent, transmitted. Cross sections of paint structures studied under 100—200 χ magnifica tion show clearly the stratography of the painting—i.e., how it was built up from the support and of what pigments the layers are com posed. For example, a rich lumi nous maroon from a 15th century Flemish painting may owe its beauty to an underlayer of fiery vermillion. Cross sections of ce ramics, bronzes, and even papers give extremely valuable information in determination of what treatment should be applied. Although every conservation lab oratory relies heavily on traditional analytical methods, most have spe cialized in some area of instrumen tal analysis. More and more, con servation chemists are tackling spe cific research problems, either or ganic—i.e., media, varnishes, dyes and adhesives—or inorganic pig ments, metals, ceramics, and stones. Because of space limitations, it is possible to mention only a few of

Figure 9. Left, " L ' H i v e r " by Van Gogh, Norton Simon Foundation Collection. Normal photograph and radiograph ( 3 0 kV, 5 mA, 1 m i n , 30-in. distance). Right, Van Gogh used one of his earlier canvases of a " W o m a n S p i n n i n g " t o paint winter scene Radiograph is so clear because first painting was done with lead white pigment, whereas in top of winter scene, zinc white, a less dense pigment, was used

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ANALYTICAL CHEMISTRY, VOL. 4 4 , NO. 1 , JANUARY 1 9 7 2


Figure 10. Left, normal photograph and right, radiograph of bronze " B u d d h a , " Gupta period, ca. 6th century, Indian, Los Angeles County Museum of Art Radiograph (250 kV, 6 mA, 10 min, 40-in. distance) shows modern repair in left 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. T h e 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 be 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, but with further work it m a y 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 at the Los Angeles County M u seum of Art with the MS902 mass spectrometer for analysis of media in Indian miniature paintings (Figure 12). T h e 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 M m e . Flieder (10) enables identification of the various gums. Individual components are further studied through mass spectrometric analysis. The next

phase of study on the Indian miniature research at the Conservation Center is the identification of organic pigments. More progress has been made in the field of inorganic analysis, partly because any organic m a t e rials 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 at the Freer Gallery of Art has pioneered the study of ancient Chinese bronzes (11). His definitive work combines wet chemistry and emission spectrometric analyses to determine major, minor, and trace elements of bronze ceremonial vessels. Metallographic studies on etched sections and microscopic surface studies along with radiographs and X - r a y diffraction analysis have enabled Gettens to determine composition, fabrication methods, surface decoration techniques, and patination types. T h e monumental nature and classical quality of Getten's research have established the standard for future research on a r t technology.

Neutron radiograph courtesy North American Rockwell

Atomics

International,

Figure 1 1 . Neutron radiograph of Chinese bronze ceremonial vessel, " T i n g , " 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, authentica tion, and treatment has prompted the conservator to rely heavily on new, sensitive techniques and to re fine sampling and sample handling so t h a t he can deal with extremely small specimens. T h e techniques briefly reviewed in the foregoing paragraphs are b u t a few of the many promising analytical tech niques in current use (15). Treatment of Art Objects

Figure 12. MS902 mass spectrometer at Los Angeles County Museum of Art, Con servation Center Instrument was gift of Mr. and Mrs. Stanton Avery

X - r a y diffraction techniques have become important for pigment stud ies not only because of their sensi tivity but also because of the differ entiation of crystal structure {12). This is important when dealing with materials chemically similar but with different crystal designs—i.e., azurite vs. malachite or chrysocolla. Combined with emission spectrography or mass spectrometry, this pro vides a thorough and accurate analysis. Inorganic mass spectrometry has been successfully applied to art ob jects, especially for metals and pig ment analysis (13). Currently, the Los Angeles County M u s e u m of Art is using mass spectrometry to study a large group of Luristan bronzes approximately 3000 years old. The small sample size (milli gram 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 ob tain accurate trace analysis with other techniques. Mass spectrom etry has also been applied t o pig ment studies (European easel paint ings, Indian miniatures, etc.) ; cur rently, a complete collection of pig ments (Forbes Collection) provided by the Conservation Center of N e w 30 A

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York University is being finger printed in Los Angeles. Recently, X - r a y fluorescence has been used a t the Winterthur M u seum by Hanson for studies of sil ver objects. The technique is ex tremely useful as it is not necessary to remove a sample of the object but simply to focus on a surface zone. H e has so far been able to establish differences in British ster ling and American silver of con temporaneous dates. William Young at the Conserva tion Laboratory of the Boston M u seum 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 about 50—80 μ in diameter and the easy analysis of nonmetallic objects. I t is also extremely useful on paintings

The most difficult and demanding task facing the Conservator is the treatment of an art object. I t is impossible to discuss here all types of deterioration which a r t objects undergo, each of which m a y require a unique treatment process if pres ervation is to be ensured. Art ob jects are individuals by their very definition, and each must be studied to determine its makeup and prop erties. Only after a thorough study and much testing can the proper treatment be developed. The treatment of paintings re quires considerable experience and knowledge of painting techniques. The nature of the painting support, whether canvas, panel, metal, glass, paper, or other, will greatly influ ence the decision as to w h a t should be done to preserve it (Figure 13). On the support is a rather complex structure of ground and design lay ers. These may be any one of nu merous types of paint—i.e., oil, egg tempera, glair (white of egg), watercolor (gum arabic), distemper (animal glue), or a synthetic resin (acrylic or v i n y l ) . Often the ground layer is one type of medium —i.e., glue with drying oil or egg tempera on top. T o further com-

Varnish Coating Pigment Layers Gesso Canvas Glue Panel

Figure 13. Schematic drawing of structure of early Italian painting shows complex structure f r o m panel support t o surface coati ng



Figure 14. "Portrait of Viscount B a r r i n g t o n " by Gilb e r t Stuart, A m e r i can, late 18th—early 1 9 t h c e n t u r y , Los Angeles County M u s e u m of A r t Painting is shown during cleaning process w i t h varnish removed f r o m left side and s m a l l rectangle in right center area. Effect of discolored varnish can be seen most easily in face but is also noticeable in cloak where details and highlights have appeared. Photograph was made without applying wetting agent or varnish in cleaned area

New Catalog 1971-72

plicate the matter, a surface coating is usually present of natural soft resin (damar, mastic), wax, glue, natural hard resin (copal, a m b e r ) , or synthetic resin (acrylic, v i n y l ) . Not only are we faced with a complex structure of materials with vastly different chemical and physical properties, b u t t h e technical idiosyncrasies of each artist must be considered. Perhaps the most complex process is safe removal of varnish and r e touching 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 a r e encountered occasionally. Soft resin varnishes not only discolor badly, but they also embrittle and crack with age and lose their protective value. T h e " P o r t r a i t of Viscount B a r rington" by Gilbert S t u a r t (Figure 14) illustrates t h e detrimental effects of varnish on t h e 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 t h e varnish film without disturbing t h e original oil medium. Since the linseed oil polymers in the paint m e dium cross-link with age, they become 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—i.e., early English paintings by artists such as Reynolds, Morland, and Constable often contain oleo-resinous media which have such a high resin content t h a t normal crosslinking of t h e oil does not occur. The problem of removing varnish from oil-resin films can usually be solved by utilization of a technique called "reforming" {9). T h e surface film is sprayed with a slow evaporating solvent mixture and left for a period ranging from a few hours to a week. T h e 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. I t is believed t h a t t h e swelling caused by t h e initial spray solvent mixture breaks secondary linkages in the resin molecules which would require months to be reestablished. Two other examples will illustrate more complex problems where large areas of t h e original surface have

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ANALYTICAL CHEMISTRY, VOL. 4 4 , NO. 1 , JANUARY 1 9 7 2

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Figure 15.

" A S i b y l " by Jusepe de Ribera, Spanish, 17th century, San Diego M u s e u m of Fine Arts

Left, before treatment; center, radiograph (30 Kv, 5 mA, 1 m i n , 30-in. distance) of lower left portion shows child's head under visible surface; right, after treatment

Figure 16.

" T h e M a r t y r d o m of Pope C a i u s " by Lorenzo Monaco, Italian, 15th century, Santa Barbara Museum of Art Left, before t r e a t m e n t ; right, after treatment

been repainted by an early restorer to the extent t h a t 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 15), came to the laboratory for examination. Radiographs of t h e lower left q u a d r a n t revealed a child's head under the visible surface. Ultraviolet examination indi32 A

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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, which was oil, b u t 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 be restudied by a r t historians to correctly identify the subject matter.

ANALYTICAL CHEMISTRY, VOL. 4 4 , NO. 1, JANUARY 1972

T h e second example is an egg tempera painting on poplar panel by Lorenzo Monaco representing " T h e M a r t y r d o m of Pope C a i u s " (Figure 16). T h e 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 be recorded by using photographic techniques, b u t a cross section made

Figure 17.

" A n a t o l i a n B u l l , " 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 sur face was in unusually good condi tion. In the armor, the areas which had been overpainted a dark blue color show traces of silver leaf which would have given a rich me tallic luster in contrast with the sur rounding gold. Structural work on paintings of ten requires lining of the original canvas, or on panels, applications of moisture barriers, or sometimes transfer of the original to 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 thermo plastic material adheres the two t o gether. Lining adhesives require more research. Traditional waxes or mixtures of waxes, resins, and balsams have been used. These ad hesives have been favored because the process is reversible simply by reheating, and they also provide a certain amount of protection from humidity changes. Modern syn thetic waxes or mixtures will prob ably yield a more neutral and dur able product once enough research is done by conservators on their aging properties. Cleaning of metals is another ex acting process since their natural patinas, usually carbonates or ox ides of copper on bronzes, often must be preserved. Surface dirt and resinous accretion from an I n dian bronze was removed mechani cally with brushes and scalpels without affecting the green mala chite surface. T h e base of the bronze which had a heavy accretion 34 A

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was first bombarded with ultrasonic waves while in a detergent bath to soften the impacted dirt layer; then it could be easily removed. If it is necessary to convert or re move the patina in a cleaning pro cess, electrolysis can be employed. T h e Anatolian bull (Figure 17) shows the effectiveness of electroly sis in revealing a silver surface. The piece was first wound with cop per 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 a p plied. 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 ex cavation of the area and packing with silver oxide. The silver oxide combines with the copper chlorides to form silver chloride which is in soluble and will stop further de terioration. Where entire objects require treatment for "bronze dis ease," they can be soaked in a solu tion of sodium sesqui carbonate ( 5 % ) . The piece is washed fre quently until chlorides can no longer be detected in the wash water. Graphic arts such as prints and drawings have often been damaged owing to negligence and poor fram ing practices. Pulpwood cardboard, extremely acidic (pH » 4.5), was for many years the most popular type of mounting and matting m a terial. Of course, the acidic prop erty of the surrounding materials migrates into the original paper and causes embrittlement and discolora tion. Unlike easel paintings where damage to support does not always mar the design itself, the paper is usually an integral part of the

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

graphic expression, and deteriora tion can cause a loss in quality. I n addition to removal of the acidic materials and replacing them with chemically neutral m a t t boards, the original paper often requires bleach ing (16) to remove stains and dis coloration, and deacidification to prevent further deterioration. D e acidification is accomplished by a p plication of a magnesium bicarbon ate to the paper to neutralize the p H (17). I n next month's issue the authors will discuss some of the more sig nificant conservation research proj ects and techniques of analysis. References

(1) D. Coekelbergs, "Precisions sur la vie et L'oeuvre du Peintre-Restaurateur Bruxellois Frederic Dumesnil (vers 1710-91," Bulletin, Institut Royal du Patrimoine Artistique, Brussels, Bel gium, 11, 174 (1969). (2) C. L. Eastlake, "Methods and Mate rials of Painting of the Great Schools and Masters," Vol I, II, Dover Publica tions, New York, N.Y., 1960. (3) E. Berger, "Beitrage zur Entwickelungs-Geshichte der Maltechnik," 4 vol, Munich, Germany, 1901-2; A. Eibner, "Entwickelung und Werkstoffe der Wandmalerei," Munich, Heller, 1926 ; W. J. Russel and W. L. Abney, "Report to the Science and Art Department of the Committee of the Council of Edu cation on the Action of Light on Watcrcolors," H.M. Stationary Office, Lon don, England, 1888. (4) R. L. Feller, "Control of the De teriorating Effects of Light upon Mu seum Objects," Museum, XVII (2) (1964). (5) J. R. J. Van Asperen de Bier, "Infra red Reflectography—A Contribution to the Examination of Earlier European Paintings," J. F. Duwaer, Amsterdam. Holland, 1970. (6) Β. Β. Johnson, "The Technique of Indian Miniature Paintings," Los An geles County Museum of Art Sym posium on Indian Art, to be published, 1971. (7) N . Stolow, "The Application of Gas Chromatography in the Investigation of Works of Art," in "Application of Science in Examination of Works of


WHEN νου UGHT. talk to the people who have been doing it for 25 years.

Art," Boston Museum of Fine Arts, Boston, Mass., 1967, pp 172-83. (8) R. Kleber and F . Tricot-Marckx, "Identification d'une Vernis Moderne Recouvrant la Décente de Croix de Rubens," Bulletin, Institut Royal du Patrimoine Artistique, Brussels, Belgium, 6, 63 (1963). (9) R. Feller, N . Stolow, and E . Jones, "On Picture Varnishes and Their Solvents," rev. éd., Case Western Reserve University, Cleveland, Ohio, 1971. (10) F . Fleider, Stud. Conserv., 13, 49 (1968). (11) R. J. Gettens, "Freer Chinese Bronzes, Vol I I , Tech. Studies," Smithsonian Inst., Washington, D.C., 1969. (12) H. Barker, "Spectrographic and Xray Diffraction Methods in the Museum Laboratory," in "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 Spec-

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Conservation," several articles on conservation, and at the moment has two definitive articles in press, "Technique of Indian Miniature Paintings," and "South Indian Bronzes."

Ben B. J o h n s o n , Head of the Con servation Center, Los Angeles County Museum of Art, received his BA in mathematics at the Col lege of William and Mary and his MA in art history at the Institute of Fine Arts, NYU. He received the Certificate in Art Conservation from the Conservation Center of NYU. In Italy he studied at the Uffizzi with Lionetto Tintori and later received a Diploma in Art Conservation from Ghent Univer sity. In 1964 he became Conserva tor of European Paintings at the Freer Gallery of Art, Smithsonian Institution. In 1967 he established the Conservation Center of the Los Angeles County Museum of Art and was appointed Lecturer in Art Con servation in the Graduate Art His tory Department at UCLA. A Fel low of the Institute for the Conser vation of Antiquities and Works of Art and a Consultant Fellow of the Conservation Center, Institute of Fine Arts, ATYU, he has lectured widely in museums on the West Coast. He has published a small book entitled "Introduction to Art

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trometry," IIC-AG Technical Papers 1968-70, Conservation Center, NYU. New York, N.Y., 1970, pp 47-58. (14) W. Young, "The Laser Microprobe and its Application to the Analysis of Works of Art," in "Application of Science in the Examination of Works of Art, Boston Museum of Fine Arts, Boston, Mass., 1967, ρ 230. (15) For further reading, see "Studies in Conservation," Aberdeen University Press, Aberdeen, Scotland, published quarterly, 1955—present ; also, "Recent Advances in Conservation," G. Thomp son, Ed., Butterworths, London, En gland, 1963. (16) For various bleaches, see H. J. Plenderleith, "The Conservation of Antiqui ties and Works of Art," Oxford Univer sity Press, London, England, 1956. (17) W. J. Barrow, Spray Deacidification Permanence/Durability of the Book III, W. J. Barrow Research Laboratory, Richmond, Va., 1964.


Thomas Cairns, Conservation Chemist for the Los Angeles County Museum of Art, received his PhD degree in chemical spec troscopy from the University of Glasgow, Scotland, in 1965. He joined Heyden and Son, Ltd., as publishing director in 1965 and served in this capacity until his ap pointment at the Museum in June 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 sum mer session lecturer in chemistry at UCLA, 1968—71, and is a science advisor to the Food and Drug Ad ministration in Los Angeles. Cur rently, Dr. Cairns is engaged in the application of mass spectrometry in an attempt to establish the origin of art objects via their trace analysis.

Art Conservation: Culture Under Analysis - Analytical Chemistry (ACS

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