“PICASSO IN THE METROPOLITAN MUSEUM OF ART”: ANINVESTIGATION OF MATERIALS AND TECHNIQUES

JULIE ARSLANOGLU, SILVIA A. CENTENO, SHAWN DIGNEY-PEER, ANDISABELLE DUVERNOIS

Department of Scientific Research, The Metropolitan Museum of ArtPaintings Conservation Department, The Metropolitan Museum of Art

The exhibition “Picasso in The Metropolitan Museum of Art” presented the unparalleled opportunity toexamine the working methods and materials of Pablo Picasso’s paintings in the museum’s collection, worksin total, covering a span of over years. All paintings were comprehensively examined and studied using infraredreflectography and x-ray radiography. The paintings with paint surfaces that visually presented qualities associatedwith alkyd, enamel, or house paints were analyzed. Four paintings presenting such significant characteristicsemerged from the group and are the focus of this study. Pigment and binding media analyses indicated the possibleuse of non-traditional artist’s paints but not necessarily house, alkyd, or enamel paints. Picasso’s infinite creativitywas reflected in his experimental nature with materials. Specifically, his manipulation and alteration of the oilmedium, which directly impacted the appearance and handling properties of the paint, must be taken intoaccount. Ultimately, the results of this study illustrate the difficulty in identifying house, boat, or other non-tra-ditional artist’s paints by visual examination alone and the challenges of their analytical characterization. Our ana-lyses showed the presence of traditional artist’s materials of the time period but did not definitively identify chemicalmarkers of house or other non-traditional artist’s paints.

KEYWORDS: Picasso, pigments, binding medium, house paints, infrared reflectography, x-ray radiography

. INTRODUCTION

Pablo Picasso’s (–) use of both artist’s andnon-traditional artist’s paints in the s and s,and as early as the s, has been established(Richardson and McCully ; Crook and Learner; Koussiaki ; Gautier et al. ). It hasalso been demonstrated that Picasso used both artist’sand non-traditional artist’s paints within a singleartwork and possibly even mixed together (Cowling; Gautier et al. ). Numerous primarysources comment on Picasso’s use of early housepaints, specifically the brand Ripolin. As early as, his use of Ripolin paint is mentioned in lettersto his dealer Daniel Henry Kahnweiler (Richardsonand McCully ). According to his friend RolandPenrose, Picasso said he liked to mix Ripolin Mat (acommercial enamel-based paint) with ordinary oilcolors because it dried fast and became very hard(Cowling ). His friend and patron Gertrude Steinalso famously wrote about his use of Ripolin (Stein) and store receipts dating from werefound in Picasso’s archive itemizing Ripolin brand

paint (Blanc de Neige) (McCully ). Ripolin wasthe most popular house paint of the time and its namebecame synonymous with any house paint.

The accurate characterization of house or otherindustrial paints in artwork from the early thcentury is challenging because many early industrialpaints were composed of the same materials as tra-ditional artist’s paints. In this study the term “industrialpaint” includes house, boat, and any other paint thatPicasso may have experimented with that was not a tra-ditional artist’s tube paint. Oil-based house paints wereavailable in the s and s as were oil paintsbased on nitrocellulose and alkyd formulations(Crook and Learner ; Capitelli ; Learner; Standeven , ).

At the start of the century, the most widely used pro-tective and decorative paints were based on oil, naturalresins, and gums and thus were chemically similar toartist’s oil paints (Crook and Learner ; Standeven, ). Linseed was by far the most commonlyused drying oil in both artist’s and industrial paints.The late th and early th centuries saw the inclusionof many new materials in industrial paints and some

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artist’s paints, including rosin-modified ester gum andsemi-drying oils (for example, soybean and sunfloweroils) and non-drying oils (for example, castor oil) (Stan-deven ). Furthermore, the qualities of naturalproduct-based (i.e. natural resins, oils, and gums)paints, as opposed to later formulations that containedmodified oils and synthetic resins, varied widelydepending on whether they were used for interior orexterior painting (Standeven ). The fact that man-ufacturers failed to document alterations made to theirformulations has further complicated the analyticalcharacterization of these paints and made these resultsdifficult to interpret meaningfully (Standeven ,). Where analyses have been attempted, the lackof appropriate reference materials also prevented con-clusive results (Koussiaki ; Gautier et al. ).The chemical composition of paints affects their

aging behavior as well as their response to conservationtreatments. Over time, changes in gloss or color mayresult from the manufacturer’s formulation; inaddition, conservation treatments involving the use ofsolvents, water, or mechanical action, may altersurface properties (Standeven ). Ongoing researchto describe and characterize artist’s and house paintsfrom the early th century contributes significantlyto the interpretation of analytical results and the accu-rate descriptions of artwork (Standeven ; Gautieret al. ). It is also essential to analyze representativereference materials from the same time period in orderto support the interpretation.In museum contexts specific visual characteristics

have been used to describe paint that was assumed tobe made for house or industrial use. In the literaturethese paints are often described as “enamel” and theirattributes include deep saturated colors, relativelyglossy surfaces, soft rounded edges, and lack of crispbrush strokes due to the leveling quality of the paint(Crook and Learner ; Gautier et al. ). Oftenthere is no supporting technical analysis.In , the exhibition “Picasso in The Metropolitan

Museum of Art” presented for the first time all theartist’s works held in the Museum’s collection sincehis iconic portrait of Gertrude Stein () enteredthe Museum at her bequest in (Tinterow andStein ). A total of paintings, drawings, sculptures and ceramic plaques, and nearly printscompose the collection, providing a large sample ofPicasso’s extraordinary and eclectic output throughouthis long career, and establishing the Museum as a sig-nificant repository of Picasso’s art.This exhibition presented an unprecedented opportu-

nity to meticulously research each work. This includedart historical significance and contextualization, prove-nance, exhibition histories, and comprehensive techni-cal examinations involving imaging and scientificanalyses. This research helped to establish the sequence

of Picasso’s often-complex compositions, to identify thepresence of unknown underlying compositions, and torecord his proficiency in a multitude of materials andtechniques. All findings are presented in the comprehen-sive exhibition catalogue, which signified the culmina-tion of this collaboration between museum curators,conservators, and scientists (Tinterow and Stein ).Of the Picasso paintings studied for this exhibition

and its accompanying catalogue, four paintings dis-played paint layers showing significant visual, physical,and textural characteristics that seemingly differedfrom traditional artist’s oil paint. The paint layers ofthese four paintings generally display a rich creamythickness with high gloss, often exhibiting fine pitting.The paint levels smoothly on the canvas, or on under-lying layers, and often pools with rounded edgeslacking any stiff brushstrokes. Conversely, it sometimesexhibits a very thin, fluid consistency that uncontrolla-bly drips and runs down the surface of the painting.These descriptions are often used when describing thevisual appearance of enamel or gloss house paintrather than artist’s paint.The four paintings exhibiting these characteristics

that are included in this study are (in chronologicalorder) Harlequin () MMA# .., TheDreamer () MMA# .., Reading at aTable () MMA# .., and WomanAsleep at a Table () MMA# ... For thisstudy, these were divided in two distinct groups: paint-ings showing thick, glossy, and smooth leveling paintlayers (The Dreamer and Reading at a Table); andpaintings showing thin, glossy, and dripped paintlayers (Harlequin and Woman Asleep at a Table).As underlying layers may affect the appearance of

subsequent applications of paint, infrared reflectogra-phy (IRR) and x-ray radiography were undertaken tosee what was beneath visible paint films. Further analy-sis was undertaken as necessary with the followingtechniques: x-ray fluorescence (XRF); Raman spec-troscopy; Fourier transform infrared spectroscopy(FTIR); pyrolysis–gas chromatography–mass spec-trometry (Py–GC–MS); and scanning electronmicroscopy–energy dispersive spectroscopy (SEM–EDS). All instrumentation and procedures are describedin appendix .

. THE PAINTINGS

. FIRST GROUP: THICK, GLOSSY, SMOOTH LEVELING PAINT

PASSAGES

The Dreamer () (fig. a) belongs to a vast groupof paintings made between and that reflectsthe artist’s change in mood, palette, and imagery to anair of erotic fulfillment and relaxation (Dabrowskia). It is one of the many compositions depicting

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Marie-Thérèse Walter. According to the inscription onthe stretcher, it was executed in July at theChâteau de Boisgeloup outside of Paris. The Dreamerdisplays a colorful palette and the rounded, expressiveforms exude not only physical pleasure but the pleasureof rendering them in paint (Dabrowski a). Thepaint has a soft buttery quality and the textures of the

brushwork suggest that it was applied quickly anddirectly. The painting is quite heavy for its size as aresult of its complex layer structure. Some of theselayers may be seen by looking through cracks andskips in the paint film. As may be seen in the infraredreflectogram and the x-ray radiograph these layers areassociated with at least two significant changes in the

FIG. . Pablo Picasso, The Dreamer, . Oil on canvas, . × . cm, TheMetropolitanMuseum of Art, New York, TheMr and Mrs Klaus G Perls Collection, (..). Photographs taken in normal light (a), normal light (detail) (b), andraking light (detail) (c). © Estate of Pablo Picasso/Artists Rights Society (ARS), New York; Courtesy of The PhotographStudio and The Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, New York.

FIG. . The Dreamer, infrared reflectogram (a) and x-ray radiograph (stretcher bars digitally reduced) (b) with several compo-sitional changes outlined. © The Metropolitan Museum of Art; Courtesy of The Sherman Fairchild Paintings ConservationCenter, The Metropolitan Museum of Art, New York.

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composition (figs. a, b). These changes are apparentas heavily textured areas that do not relate to brush-work in associated passages of the visible paint film(figs. b, c). Boldly shifting entire elements of thepicture with no apparent hesitation, The Dreamer is aprime example of Picasso re-working his paintingsspontaneously and organically with little or no attach-ment to intermediate steps. This unvarnished paintingdisplays distinct areas of glossy paint (fig. a). Othereffects observed are wrinkling, pitting, and passageswhere overlying layers completely mask the texture ofunderlying areas (leveling) (figs. b, c, d).Reading at a Table () (fig. a) is a rare depiction

of Marie-Thérèse in the midst of a sedentary, virtuous,intellectual pursuit (Dabrowski b). Unlike por-traits that emphasize Marie-Thérèse’s sexuality andphysicality, here Picasso represents her as his etherealgoddess-like muse. Similar to The Dreamer, paint wasapplied directly and in many layers. Skips in the paintfilm reveal underlying layers of blue, green, red, andgray paint. Also, there are broad passages of texturein the paint film that are not related to the associatedbrushwork in the final composition. The areas thathave the thick, glossy, and buttery characteristics com-monly associated with enamel paint were the areas offlesh paint, where the soft, thick, and pronouncedbrushstrokes with soft-edged peaks were mostevident. This is especially apparent in the features ofMarie-Thérèse’s face (fig. b). In addition, there arepaint drips and textures that have held their shapeand do not appear to have flattened upon drying. Thepainting was examined with IRR and x-ray radiogra-phy, which, other than revealing several changes inthe composition, was not useful in further explainingthe appearance of the paint film in these areas.

. SECOND GROUP: THIN, GLOSSY DRIPPED PAINT PASSAGES

The commedia dell’arte character Harlequin was oneof Picasso’s favorite and recurring subjects. In his version ofHarlequin (fig. a), Picasso’s reinterpretationcombines Synthetic Cubist elements and those of Surre-alism executed in muted colors of white, black, gray,brown, beige, and green (Dabrowski c). Thecentral black profile silhouette strongly suggestsMarie-Thérèse’s characteristic facial features, whichPicasso would develop and transform in his paintingsand sculptures through the late s. Unlike TheDreamer, Harlequin shows Picasso’s ability forrestrained execution. He drew the composition withthin graphite lines directly onto the ground layer andproceeded to precisely paint in all the outlined fields.He made no changes to this composition: it is directand precise. All outlines are clearly visible with IRRand also under high magnification. In general, thepaint layer in Harlequin was applied thinly and often

reveals the canvas texture. However, it presents extre-mely varied textures: from smooth and lean to creamyand gritty. The gray paint used in the bottom rightcorner is of a thick nature but has a very smooth andcreamy surface that levels on the canvas with arounded texture. Within the same passage the paintsometimes appears both thin, leveling into the canvastexture, and relatively thick, creamy, and glossy, retain-ing soft-edged peaks. Pitting is also apparent in some ofthe paint passages, and clearly does not relate to anypre-existing underlayer.Woman Asleep at a Table () (fig. a), yet

another depiction of Marie-Thérèse, shows her asleepat a table in the small country house ofTremblay-sur-Mauldre, near Paris, which Picassorented from the art dealer Ambroise Vollard (Dab-rowski d). Picasso’s minimal palette of blacks,whites, and shades of gray applied over a red-brownimprimatura layer, suggesting grisaille technique,complements well what appears to be a nocturnalscene. In this painting Picasso achieves yet anotherapproach to painting a composition. Unlike Harlequin,he did not execute Woman Asleep at a Table in a sys-tematic way. He alternated between outlining theelements both under and over the paint layer andworking wet-in-wet, utilizing the transparency of thepaint layer while making numerous changes in theprocess. All the changes, concentrated in the elementsof the background, are clearly visible through thepaint layer. He defined all outlines either with medium-rich black paint or by using the leaner and drier red-brown imprimatura layer in reserve. In particularplaces he also used charcoal to trace black lines ontop of the paint layer. Such final accents often leftgrainy graphite particles embedded in the fluid paintlayer, creating sharp textural contrast to the overallglossy paint layer. In this work, the paint layersexhibit all of the characteristics of an enamel-likepaint: highly glossy, medium-rich, fluid, and levelingflat on the imprimatura layer (figs. a, b). This paint-ing was never varnished, however a pronounced gloss,not customarily associated with an unvarnished tra-ditional oil paint layer, is especially evident when thepainting is viewed in specular light (fig. b). In areaswhere the artist let the fluid paint run freely, the thickdrips of paint seem to have congealed in place, mini-mally disturbing the underlying paint (fig. c).

. RESULTS

. FIRST GROUP

.. THE DREAMER ()A cross section prepared from a sample taken from an

area of consolidated loss at the bottom of the left edge ofthe painting revealed the complexity of the paint layer

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structure (fig. ). In this sample, at least paint layersmay be distinguished; in situ non-invasive XRF analysis,therefore, would not have provided insight into theelemental composition of the individual paint layers.SEM–EDS analysis of this sample indicated that the pig-ments are typical of those found in artist’s paints(table ), and that most, but not all of the paints,contain varying amounts of zinc white (zinc oxide,ZnO) and have sulfate fillers (gypsum or bariumsulfate). This could possibly represent Picasso’s use ofboth house (high ZnO content) and traditional artist’s(no or low zinc content) paints in a single artwork(Gautier et al. ; Standeven ). Notably, thegreen paints contain green pigments as opposed to a

mixture of blue and yellow pigments that is more typi-cally found in house paints (Gautier et al. ).

Analysis of the different layers in this cross sectionby ATR–FTIR, and of isolated layers by FTIR in thetransmission mode, showed the presence of heavymetal carboxylates. Heavy metal carboxylates(soaps) are compounds formed by heavy metal ions,such as lead, zinc, or copper, and fatty acids. In adried and aged paint film, these compounds resultfrom the reaction of the ions in the inorganic pigmentswith the fatty acids in the binder. Over time these com-pounds may aggregate and become visible as whitish,translucent inclusions. However, in the early stages ofthese reactions, they are detectable by analytical

FIG. . Details from The Dreamer: (a) glossy paint, (b) wrinkling, (c) pitting, (d) leveling. © The Metropolitan Museum of Art;Courtesy of The Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, New York.

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techniques but they may not be visible under opticalmagnification. In paint manufacture heavy metal car-boxylates can be added directly to the paint formu-lation to increase the drying rate of the paint orachieve other working properties. In the case of TheDreamer no inclusions with morphologies typical ofthose observed in saponified paints (Mahon andCenteno ; Centeno and Mahon ) arevisible in this sample. Metal carboxylates can form

during the aging process of the paint (Boon et al.; Robinet and Corbeil ; Nevin et al. ;Centeno and Mahon ) or can be deliberatelyadded to the original formulation of the paint – asdriers, for example (Mallegol et al. , ; vanGorkum and Bouwman ; Boon et al. ).While care was taken to isolate the different paintlayers, the binding media analysis took into accountthe presence of a consolidant identified by Py–GC–MS

FIG. . Pablo Picasso, Reading at a Table, . Oil on canvas, . × . cm, The Metropolitan Museum of Art, Bequestof Florene M Schoenborn, in honor of William S Lieberman, (..). Overall photograph taken in normal light (a)and a detail of thick paint (b). © Estate of Pablo Picasso/Artists Rights Society (ARS), New York; Courtesy of The Photo-graph Studio and The Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, New York.

FIG. . Pablo Picasso, Harlequin, . Oil on canvas, . × . cm, The Metropolitan Museum of Art, The Mr and MrsKlaus G Perls Collection, (..). Photograph taken in normal light (a) and under ultraviolet light (b), and x-rayradiograph of Harlequin (c). © Estate of Pablo Picasso/Artists Rights Society (ARS), New York; Courtesy of The Photo-graph Studio and The Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, New York.

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as n-butyl methacrylate (n-BMA). Analysis of the bulksample and of individual isolated layers by Py–GC–MSdemonstrated that the binder appears to be semi-dryingoil with a trace of natural wax (table ). No markersfor nitrocellulose or alkyd paints were found (Challinor; van der Weerd et al. ; Learner ). Whileall of the paints had similar binding media profiles,they were not identical. For example, relative to otherpaint layers, the black paint layer in this sampleappears to be the least dry (having the highest concen-tration of oleic acid, a monounsaturated free fatty acid)and the most medium-rich (having the highest glycerolcontent).

.. READING AT A TABLE ()The pigments identified in this painting are tra-

ditional artist’s pigments (table ). No zinc-containing

materials were detected in the samples analyzedalthough heavy metal carboxlyates and sulfates wereobserved by FTIR. As in the case of The Dreamer, nosoap aggregates are visible so it is not possible to deter-mine whether the presence of these heavy metal carbox-ylates is due to an incipient saponification process in thepaint or if they have been added as driers.

Results of the Py–GC–MS analysis indicate a possiblemixture of a drying and a semi-drying oil with traceamounts of a natural wax and resin. No markers fornitrocellulose or alkyd paints were found. This bindingmedia analysis took into account the presence of anearlier varnish, identified as n-BMA/iso-BMA (:) byPy–GC–MS, and a wax-lining adhesive that mayaccount for the natural wax detected. The trace resincomponent was found to be a mixture of diterpenoidand triterpenoid resins; the amount of this triterpenoid

FIG. . Pablo Picasso, Woman Asleep at a Table, . Oil and charcoal on canvas, . × . cm, The MetropolitanMuseum of Art, TheMr andMrs Klaus G Perls Collection, (..). Photographs taken in normal light (a) and specu-lar light (b). © Estate of Pablo Picasso/Artists Rights Society (ARS), New York; Courtesy of The Photograph Studio andThe Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, New York.

FIG. . Details fromWoman Asleep at a Table, (a) leveling paint showing rounded edges, (b) leveling paint lacking stiff brush-strokes, and (c) drips of paint congealed in place. © TheMetropolitanMuseum of Art; Courtesy of The Sherman Fairchild Paint-ings Conservation Center, The Metropolitan Museum of Art, New York.

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resin was extremely small and may be due to a contami-nation from the wax lining. The diterpenoid componentis also very small and may derive from the use of turpen-tine as paint thinner or from a siccative resin, although itis not possible to determine its origin with certainty.

. SECOND GROUP

.. HARLEQUIN ()During examination of Harlequin under ultraviolet

(UV) illumination, a strong green fluorescence wasobserved in distinct areas (fig. b): the light brownborder on the right and bottom edges and along partof the left edge, the light gray paint in the lower rightcorner, also filling the eyes, the mouth, and ear of thecentral figure, and the middle brown area suggestingthe upper back of the central figure. The painting wasx-ray radiographed (fig. c) to establish whether therewas any relationship between the strong green fluor-escence seen under UV illumination and the radio-opacity of those pigments.When the x-ray radiograph of the painting is com-

pared to both the normal light and UV-illuminatedphotographs (figs. a, b, c), there appears to be a cor-relation between the UV-induced visible fluorescenceand the location of less radio-opaque areas in thex-ray radiograph. XRF analysis of two similarmedium brown paints – one that fluoresces and onethat does not – showed that the fluorescent areas con-tained more zinc and less lead than the non-fluorescentpassages (fig. ). Therefore, the florescence appears tocorrelate with the presence of zinc white. It is not

FIG. . The Dreamer, paint cross section, visible illumina-tion, original magnification: ×. © The MetropolitanMuseum of Art; Courtesy of The Sherman Fairchild PaintingsConservation Center, The Metropolitan Museum of Art,New York.

TABLE . PIGMENTS AND BINDING MEDIA ANALYSES RESULTS FOR THE DREAMER ()

Paint color Pigments Binding mediumd,e

Light green Lead whitea,c,d, barium whitea, zinc whitea, chrome greena, heavymetal carboxylatesc

Not analyzed (NA)

Pink Zinc whitea, particles of cadmium reda NABlack Bone blacka,c,d, zinc whitea, heavy metal carboxylatesc Semi-drying oil, natural

waxLight green Zinc whitea,b, Pb-containing particlesa, barium whitea,b, chrome

greena, ultramarine bluea,b, heavy metal carboxylatesb,cDrying and semi-dryingoil, natural wax

White Zinc whitea, isolated Pb-containing particlesa, heavy metalcarboxylatesc

Drying and semi-dryingoil, natural wax

Light blue Zinc whitea, lead whitea,c,d, ultramarine bluea,c,d, gypsuma,c,d, heavymetal carboxylatesc

Drying and semi-dryingoil, natural wax

Dark blue Zinc whitea, lead whitea, ultramarine bluea, gypsuma, heavy metalcarboxylatesc

NA

Light blue Lead whitea, ultramarine bluea, gypsuma, Mg-Ca-containing particles(dolomite?)a, heavy metal carboxylatesc

NA

Green Lead whitea,c,d, chrome greena, Scheele’s or emerald greena, bariumwhitea,d, heavy metal carboxylatesc

Drying and semi-dryingoil, natural wax

a, SEM–EDS; b, Raman spectroscopy; c, ATR–FTIR; d, FTIR; e, TMAH–Py–GC–MS. Major components are indicated in bold.

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possible at the moment to state the origin of thisphenomenon. Studies of UV and also visible-inducedluminescence properties of materials in artworks haveshown that these properties are complex and thatthey may change with aging and upon mixing (de laRie ; Bottiroli et al. ; Miliani et al. ;Thoury et al. ; Claro et al. ; Nevin et al.; Melo and Claro ). More recently, takingadvantage of high energy sources at synchrotronfacilities, a UV-visible multispectral luminescencemicro-imaging study has shown the potential of sucha technique for identifying, localizing, and characteriz-ing semiconductor materials such as ZnO in hetero-geneous historical samples (Thoury et al. ).

The pigments identified in this painting are tra-ditional artist’s pigments and the paints also containcarbonate and sulfate fillers and heavy metal carboxy-lates (table ). No soap aggregates were observed, so

just as for the paintings discussed above, it is not poss-ible to identify the origin of these carboxylates. Bindingmedia analysis by Py–GC–MS showed the presence of adrying oil, possibly heat bodied, with a trace amount ofditerpenoid resin (possibly turpentine or siccativeresin). This media analysis took into account the pres-ence of a consolidant and of a residual varnish, n-BMA, and n-BMA/iso-BMA (:), respectively. Theonly compositional difference observed among thepaints analyzed was a small amount of natural waxpresent in a sample of a non-fluorescent brown paintfrom the right edge of the Harlequin’s hat.

.. WOMAN ASLEEP AT A TABLE ()Examination of Woman Asleep at a Table with the

unaided eye revealed Picasso’s technique as well asthe changes that he made to the composition. As men-tioned earlier, he built the painting by alternating

TABLE . PIGMENTS AND BINDING MEDIA ANALYSES RESULTS FOR READING AT A TABLE ()

Paintcolor

Pigments Binding mediumb,c

Black Carbon-based blacka,b, sulfatesb, lead whitea,b,heavy metal carboxylatesa,b

Drying oil and semi-drying oil, natural wax(trace), diterpenoid and triterpenoid resin (trace)

Orange Vermiliona, some particles of a carbon-basedblacka, sulfatesa,b, heavy metal carboxylatesa,b

Drying oil and semi-drying oil, natural wax(trace), diterpenoid and triterpenoid resin (trace)

a, Raman spectroscopy; b, FTIR; c, TMAH–Py–GC–MS. Major components are indicated in bold.

FIG. . XRF spectra of a fluorescent (green trace) and a non-fluorescent (blue trace) medium brown paint area in Harlequin,showing the higher zinc proportion in the fluorescent paint. For clarity, the scale of the spectra has been enlarged and, therefore,the lead L- and zinc K-lines are out of range.

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between outlining the elements under and over thepaint layer, going back and forth, working wet-in-wet,utilizing the paint transparency yet also making numer-ous changes. A few examples are illustrated in figure .However, neither x-ray radiography nor IRR revealedany additional information in regard to the paint’svisual characteristics.All of the paints analyzed contain significant

amounts of zinc white (table ) and the pigments ident-ified all appear to be traditional artist’s pigments. Theexception is the shiny black paint used, for instance,to outline the legs of the table, which contains theanatase form of titanium dioxide. Interestingly, eventhough the paints had high zinc content, similar to thefluorescent paints in Harlequin, none of the paints in

Woman Asleep at a Table fluoresced with the sameintensity. Carbonate or sulfate fillers were only detectedin the flat black paint but heavy metal carboxlyateswere found in all the paints except the red imprimaturaand the ground. As in the case of the paintings discussedabove, no soap aggregates were observed, so it is notpossible to state the carboxylates’ origins. Thebinding medium for all the paints analyzed was foundto be a drying oil with a trace amount of diterpenoidresin by Py–GC–MS. As above, the trace amount ofditerpenoid resin might be derived from the use of tur-pentine as paint thinner or even of a siccative resin.

. DISCUSSION

The characterization of the paints in all of these paint-ings illustrates the material complexity of artworksfrom the first half of the th century and the challengespresented in trying to make the distinction between tra-ditional artist’s paints and industrial or house paints.The customary approach to paint characterization bybinder and pigment identification is strained becauseearly industrial paints used oils and other materialssimilar to those found in artist’s paints. Even thoughthe repertoire of oils used in industrial paints expandedto include ester gum, Tung, perilla, soybean, dehy-drated castor, fish, and tall oils (Standeven ), notto mention the possibility of using oil mixtures, thecharacterization of these oils by semi-quantitativefatty acid analysis can be limited due to the similarityof fatty acid ratios within classes of oils and the lackof unique marker compounds in aged paint films (forexample, differentiating between soybean oil andsafflower oil [Schilling et al. ]).Furthermore, Standeven () reports that the

bodying of high gloss ready-mixed exterior paints

TABLE . PIGMENTS AND BINDING MEDIA ANALYSES RESULTS FOR HARLEQUIN ()

Paint color Pigments Binding mediumc,d

Light brown (right tanborder; fluorescent under UV)

Zinc whitea,b, lead whitea,b,c, carbon-basedblacka,b, calcium carbonatea,b,c, gypsuma,b,c,umber (Fe, Mn)a,b, heavy metal carboxylatesb,c

Drying oil (possibly heat-bodied),diterpenoid resin (trace)

Light gray* (square in lowerright; fluorescent under UV)

Zinc whitea,b, lead whitea,b,c, calciumcarbonatea,b,c, gypsuma,b,c, heavy metalcarboxylatesb,c

Drying oil (possibly heat-bodied),diterpenoid resin (trace)

Medium brown (right edgeof central figure’s upper back;fluorescent under UV)

Zinc whitea,b, lead whitea,b,c, calciumcarbonatea,b,c, gypsuma,b,c, umber (Fe, Mn)a,b,heavy metal carboxylatesb,c

Drying oil (possibly heat-bodied),diterpenoid resin (trace)

Medium brown (right edgeof hat; not fluorescent underUV)

Lead whitea,b,c, zinc whitea,b, carbon-basedblacka,b, calcium carbonatea,b,c, gypsuma,b,c,umber (Fe, Mn)a,b, heavy metal carboxylatesb,c

Drying oil (possibly heat-bodied),natural wax, diterpenoid resin(trace)

a, XRF; b, Raman spectroscopy; c, FTIR; d, TMAH–Py–GC–MS. Major components are indicated in bold.*Only particles of the white pigment present in the mixture were analyzed in order to investigate the fluorescence properties.

FIG. . WomanAsleep at a Table, photograph taken undernormal light with compositional changes outlined. © TheMetropolitan Museum of Art; Courtesy of The Sherman Fair-child Paintings Conservation Center, The MetropolitanMuseum of Art, New York.

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could be achieved by including zinc stearate, amongother methods. The addition of heavy metal soaps bymanufacturers could affect the fatty acid ratios usedfor quantitative analysis and significantly interferewith the accurate characterization of the oil componentin the binding medium. It has been reported that thepresence of high concentrations of ZnO in oil paintscan dramatically affect the drying mechanism of theoil leading to elevated levels of oleic acid concentrationseven in paintings over years old (Rogala et al. ;McCully ). Fully cured drying oil films typicallycontain little, if any, oleic acid as it is convertedthrough oxidation to azelaic acid. Thus high concen-trations of ZnO could affect the azelaic:palmitic acidratio commonly used for characterizing drying oils.Moreover, the presence of oleic acid may lead to theerroneous identification of semi-drying oil in theabsence of other differentiating ratios or compounds.

Pigment characterization may be able to give moreinsight. Not all traditional artist’s pigments were usedin house paints after the mid-th century (Standeven), so the absence of such pigments may indicatean industrial paint. Furthermore, it has been reportedthat house paints used combinations of pigments toobtain certain colors, for instance blue and yellow pig-ments were combined to yield green paints (Gautieret al. ). Also, ZnO was used in house paints as abulking agent or pigment, and carbonates and sulfatescould be used as bulking compounds. All of thesefactors may be significant in the distinction betweenan artist’s paint and an industrial paint, but even sothere is a limitation to what may be inferred. Forexample, high concentrations of ZnO may be inter-preted as an indicator of an enamel paint (a durable

paint made by grinding ZnO into a paste withvarnish or oil and then thinning the mixture with agum varnish or turpentine), a high gloss ready-mixedexterior or interior paint, or another industrial paint.Making the distinction between these house paints isproblematic and was deemed all but impossible asearly as due to the similar and ever changing for-mulations as well as the imprecise use of label nomen-clature (Standeven ). Furthermore, zinc whiteemerges as an artist’s pigment in the second quarterof the th century and its use increases simultaneouslywith the rise of the use of house paint use by artist’s inthe s. Artist’s paints tend not to have high concen-trations of carbonate and/or sulfate fillers; however,some house formulations do not either (Casadio andGautier ). Clearly, a combination of techniquesto identify pigments, fillers, and binding media can beused in an effort to unambiguously identify industrialpaints. However, the interpretation of the results mustbe guided by research of historic reference materialsand documentation.

. CONCLUSION

The investigation of these four paintings was performedusing equipment and instrumentation typically found incultural institutions. With the use of referencematerials, the identification of alkyd, enamel, and nitro-cellulose paints is possible; however, none of thesematerials was identified in the four paintings examinedfor this study in spite of having visual characteristicscommonly associated with such paints. All of thepaints analyzed for this study appeared to be essentiallyoil-based, both artist’s and possibly industrial paints.

TABLE . PIGMENTS AND BINDING MEDIA ANALYSES RESULTS FOR WOMAN ASLEEP AT A TABLE ()

Paint color Pigments Binding mediumc,d

Shiny white Zinc whitea,b, lead whitea,b,c, iron oxidea, heavy metal carboxylatesb,c Drying oil, diterpenoidresin (trace)

Matte white Zinc whitea,b, lead whitea,b,c, iron oxidea, heavy metal carboxylatesb,c Drying oil, diterpenoidresin (trace)

Flat black Lead whitea,c, iron oxidea, zinc whitea, barium whitea,c, calciumcarbonatea,c, heavy metal carboxylatesc

NA

Shiny black Zinc whitea,b, lead whitea,b,c, iron oxidea, carbon-based blackb, titaniumdioxide (anatase)b, heavy metal carboxylatesb,c

Drying oil, diterpenoidresin (trace)

Gray Zinc whitea,b, lead whitea,b,c, iron oxidea, carbon-based blackb, heavymetal carboxylatesb,c

Drying oil, diterpenoidresin (trace)

Brown Zinc whitea, lead whitea, earth pigmentsa, heavy metal carboxylatesc NARedimprimatura

Lead whitea, iron oxidea, zinc whitea, barium whitea NA

Ground Lead whitea,c, zinc whitea, iron oxidea, calcium carbonatec NA

a, XRF; b, Raman spectroscopy; c, FTIR; d, TMAH–Py–GC–MS. Major components are indicated in bold.

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Characterization of the oil component was based onsaturated and unsaturated fatty acid ratios and glycerolcontent: no marker compounds were found for castoror Tung oils. In paintings having a multi-layered paintcomposition, although care was taken in the isolationof the layers, contamination from other layers cannotbe ruled out and could affect the analyses.This study illustrates how the identification of paints

within this dynamic period through visual examinationalone is highly problematic. Analysis can provide moreinsight and, in order to make the most accurate identifi-cation of these house or non-traditional artist’s paints,multiple investigative tools must be used, including his-toric reference materials.

ACKNOWLEDGMENTS

The authors would like to express their gratitude to the fol-lowing colleagues: Lucy Belloli and Michael Gallagher fromThe Sherman Fairchild Paintings Conservation Center, TheMetropolitan Museum of Art (MMA); Mark T. Wypyski,Adriana Rizzo, and Marco Leona from the Department ofScientific Research, MMA; Gary Tinterow, Susan AlysonStein, Magdalena Dabrowski, Lisa M. Messinger, AsherEthan Miller, Marla Prather, Rebecca A. Rabinow, SabineRewald, Samantha Rippner, and Christel Hollewoet-Forcefrom the Department of Nineteenth-Century, Modern, andContemporary Art, MMA; Chris McGlinchey, The Museumof Modern Art; Tom Learner and Michael Schilling, TheGetty Conservation Institute; Gwénaëlle Gautier, formerlyat The Art Institute of Chicago.

APPENDIX .

INSTRUMENTATION AND TECHNIQUES

X-RAY RADIOGRAPHY AND IRR

The radiographs illustrated in this study were capturedwith a TFI “Hotshot” portable industrial x-ray unit, consist-ing of: Head and D Control, V, Hz, with arange of kV– kV, a . mm focal spot, and a . cmradiation beam. The films used were Kodak PPL oncologyfilm in ready-packs. They were processed using a refurbishedmedical Kodak X-Omat processor and were scanned and digi-tally assembled using Adobe Photoshop. Stretcher bars andhardware were digitally minimized to allow maximum legibil-ity of all underlying paint layers.

The paintings were examined with an Indigo SystemsMerlin Near Infrared camera with a solid-state indiumgallium arsenide detector sensitive to wavelengths from .to . µm. The camera was used in conjunction with a custo-mized macro lens optimized for this range. The resultingimages (infrared reflectograms) were digitally assembledusing Adobe Photoshop. These techniques were valuable inrevealing changes in the compositions but also on thespatial distribution of some of the materials used. X-ray radi-ography gave information on the presence and distribution ofheavy metal-containing pigments, particularly lead-based,

and IRR revealed the distribution of carbon-containing pig-ments often used in the underdrawings.

XRF SPECTROSCOPY

Qualitative non-invasive XRF analyses were performedusing an Artax unit equipped with a rhodium targetand a µm collimator. All spots were analyzed for equallive-times of seconds at kV and µA. The beamwas focused on the different spots using the camera attachedto the spectrometer.

RAMAN SPECTROSCOPY

Raman spectra were recorded with a Renishaw System spectrometer, using and nm lasers. The laserbeam was focused on the different layers in the paint cross-section or in the sample scrapings using a × objectivelens. Powers on the order of mW were used, with accumu-lation times between and seconds.

FOURIER TRANSFORM INFRARED MICROSPECTROSCOPY

Analyses were carried out on individual paint layers incross sections by attenuated total reflectance (ATR)–FTIRmicrospectroscopy or on scrapings of individual layers byFTIR in the transmission mode using a Hyperion micro-scope interfaced to a Bruker Vertex spectrometerequipped with a mercury cadmium telluride detector.ATR–FTIR measurements were performed using a germa-nium ATR × objective. The germanium crystal, with arefractive index of ., has an anvil design with an-μm tip. Spectra were acquired in the range –cm− at cm− resolution, with automatic background sub-traction. Between and scans were collected,depending on the dimensions of the area analyzed. Analyseswere performed on multi-layered paint samples embeddedin an acrylic resin (Technovit LC; Heraeus Kultzer,Germany). The embedded samples were dry-ground andpolished using polishing cloths of grades –,(Micro-Surface Finishing Products, USA). No furthersample preparation was necessary.

Samples for FTIR analysis in transmission mode of paintscrapings or isolated paint layers were crushed in a micro-compression diamond cell (Spectra-Tech, Oak Ridge, TN,USA) and analyzed through a × IR objective. The acqui-sition parameters were the same as for ATR and thenumber of scans ranged from to . Interpretation ofthe ATR and FTIR spectra was based on comparison withMMA and IRUG reference libraries (IRUG Spectral Data-base, Edition ) and with data reported in the literature.

PYROLYSIS–GAS CHROMATOGRAPHY–MASS SPECTROMETRY

Py–GC–MS without and with the derivitizing agent tetra-methyl ammonium hydroxide (TMAH–Py–GC–MS) pro-vided molecular information about the binders and somepigments. Analysis was performed on a Hewlett PackardN gas chromatograph equipped with a FrontierPY-iD Double-Shot vertical furnace pyrolyzer fittedwith an AS-E Auto-Shot autosampler. The GC wascoupled to a N single quadruple mass selective detector.

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Samples of µg– µg were weighed out in deactivatedpyrolysis sample cups (PY-ECF Disposable Eco-Cup LF)on a Mettler Toledo UMX Ultra Microbalance. Sampleswere then either pyrolyzed without derivatization or deriva-tized before pyrolysis. Derivatization took place in the samecup: – µl of % TMAH in methanol, depending on thepaint sample size, were added directly to the sample in thecup with a µl syringe and after minute, loaded onto theautosampler. The interface to the GC was held at °Cand purged with helium for seconds before opening thevalve to the GC column. The samples were then droppedinto the furnace and pyrolyzed at °C for seconds.The pyrolysis products were transferred directly to aDB-MS capillary column ( m× .mm× . µm) withthe helium carrier gas set to a constant linear velocity of. ml/minute. Injection with a :, :, or : split(depending on the sample size) was used. The GC oven temp-erature program was: °C for minute; °C/minute to°C; isothermal for minute. The Agilent N MSDconditions were as follows: transfer line at °C, MSQuad °C, MS Source °C, electron multiplier atapproximately V; scan range – amu. Forsamples run with TMAH, the detector was turned off until.– minutes to avoid saturation by excess derivatizingagent and solvent. Data analysis was performed on anAgilent MSD ChemStation D... and the NIST spectral libraries.

Saturated and unsaturated fatty acid ratios as well as gly-cerol estimation was used to characterize the oils in thebinding media. These values were compared against referencematerials of dried oils (linseed oil, tung oil, sunflower oil, etc.)and two Ripolin samples, one from – and the otherfrom the s–s, as well as a number of samples fromindustrial paint sample books spanning the first half of theth century from The Sherwin-Williams Co. (USA,Canada, and London, England), SoyOil Paint (Illinois FarmSuppply Co., Chicago, IL, USA), and Sargent SuperfineTung Oil Enamel paints (The Sargent-Gerke Co., Indianapo-lis, IN, USA) (McGlinchey ).

SCANNING ELECTRON MICROSCOPY/ENERGY-DISPERSIVE

X-RAY SPECTROSCOPY

SEM–EDS analyses were performed on samples previouslycoated with carbon using an Oxford Instruments INCAEnergy Microanalysis system attached to a LEO variable pressure SEM, operated under high-vacuum con-ditions with a target voltage of . kV.

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AUTHOR BIOGRAPHIES

JULIE ARSLANOGLU joined the Department of Scientific Research at The Metropolitan Museum in February as an associateresearch scientist after positions at the Victoria and Albert Museum, London and the Getty Conservation Institute, Los Angeles,among others. She holds graduate degrees in chemistry (The Pennsylvania State University) and paintings conservation (The

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Courtauld Institute of Art, London). Her primary role is the investigation of art and its materials with a focus on paintings andworks of art on paper. She specializes in the analysis of organic natural product and synthetic materials using spectroscopic, chro-matographic, mass spectrometric, and immunological techniques. Address: Department of Scientific Research, TheMetropolitanMuseum of Art, Fifth Avenue, New York, NY , USA. Email: julie.arslanoglu@metmuseum.org.

SILVIA A. CENTENO is a research scientist in the MMA’s Department of Scientific Research, where her main responsibilities includethe investigation of the material aspects of works of art, with a focus on paintings, works of art on paper, and photographs. Shehas lectured and published on a number of topics ranging from Medieval illuminated manuscripts and Renaissance paintings toth century drawings, early lithographic inks, photographic materials, and modern paints. Address: as for Arslanoglu. Email:silvia.centeno@metmuseum.org.

SHAWN DIGNEY-PEER is an associate conservator in the Paintings Conservation Department at The Metropolitan Museum of Art,where he specializes in the restoration of th century, modern, and contemporary paintings. Shawn received his postgraduateDiploma in the conservation and restoration of easel paintings from the Courtauld Institute of Art (London) in . Address:The Sherman Fairchild Paintings Conservation Center, The Metropolitan Museum of Art, Fifth Avenue, New York, NY, USA. Email: shawn.digney-peer@metmuseum.org.

ISABELLE DUVERNOIS is an associate conservator in the Paintings Conservation Department at The Metropolitan Museum of Art,where she has specialized in the conservation of th century, modern, and contemporary paintings since . She received anMA in art history and an Advanced Certificate in the conservation of works of arts from the New York University Institute ofFine Arts and the Conservation Center in . The Sherman Fairchild Paintings Conservation Center. Address: as for Digney-Peer. Email: isabelle.duvernois@metmuseum.org.

Résumé – L’exposition Picasso in The Metropolitan Museum of Art, tenue en , présentait une occasion uniqued’examiner la technique picturale et les matériaux des peintures de Pablo Picasso de la collection du musée, soittrente-quatre œuvres au total couvrant soixante années de carrière. Toutes les peintures ont été examinées et étu-diées en profondeur en utilisant la réflectographie infrarouge et la radiographie. Les peintures dont la surface pic-turale présentait des caractéristiques visuelles associées à l’alkyde, à la peinture-émail ou à la peinture de bâtimentont été analysées. Quatre d’entre elles, qui présentaient de façon marquée de telles caractéristiques, ont émergées dugroupe et constituent le point d’intérêt de cet article. Les résultats d’analyse des pigments et des liants indiquaientl’emploi possible de peintures non-traditionnelles, mais pas nécessairement l’emploi de peinture de bâtiment,d’alkyde ou de peinture-émail. La créativité sans cesse renouvelée de Picasso se reflète par le caractère expérimentalde ses matériaux. Entre autre, on doit prendre en considération sa façon de manipuler et d’altérer le liant à l’huile, cequi avait un impact directe sur l’apparence et la mise enœuvre de la peinture. Ultimement, les résultats de cette étudeillustrent la difficulté d’identifier par examen visuel seul les peintures de bâtiment, de bateau ou toute autre peintured’artiste non traditionnelle, tout autant que les défis posés lors de leur caractérisation analytique. Ces analyses indi-quent la présence de matériaux d’artiste traditionnels de cette période, mais n’identifient pas avec certitude les mar-queurs chimiques de peinture de bâtiment ou d’autres peintures d’artiste non traditionnelles.

Resumen – La exhibición ‘Picasso en el Museo Metropolitano de Arte,’ que tuvo lugar en el año , presentó unaoportunidad única de examinar las técnicas y los materiales usados por Pablo Picasso en las pinturas de la coleccióndel museo, treinta y cuatro obras en total que cubren un período de más de sesenta años. Todas las pinturas fueronexaminadas y estudiadas en forma exhaustiva usando reflectografía infrarroja y radiografía. Fueron analizadas laspinturas que presentaban superficies con características visuales generalmente asociadas con resinas alquídicas, conesmaltes o con pinturas para casas. Cuatro de estas pinturas fueron seleccionadas de este grupo y constituyen elenfoque del presente artículo. Los análisis de los pigmentos y de los medios aglutinantes indicaron que probable-mente fueron usadas pinturas artísticas no tradicionales, pero no necesariamente pinturas para casas, basadas enresinas alquídicas o en esmaltes. La creatividad infinita de Picasso se reflejó en la forma experimental con queusó los materiales. Deben ser tenidos en cuenta específicamente la manipulación y los cambios al aceite delmedio aglutinante que tienen un impacto directo sobre el aspecto de la pintura y sobre como deben ser trabajados.Los resultados de este estudio ilustran las dificultades que se deben afrontar durante la identificación puramentevisual de pinturas para casas, botes o de otras pinturas artísticas no tradicionales y los retos que presentan su car-acterización e identificación. Los resultados de nuestros análisis muestran la presencia de materiales artísticos notradicionales correspondientes al período, pero no identifican categóricamente marcadores químicos de pinturaspara casas o de otras pinturas artísticas no tradicionales.

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Resumo – A exposição “Picasso in The Metropolitan Museum of Art” de foi uma oportunidade única paraexaminar os métodos e materiais de trabalho de pinturas de Pablo Picasso nas coleções dos museus, um total de trabalhos cobrindo um período de mais de anos. Todas as pinturas foram extensamente analisadas e estuda-das com reflectografia de infravermelho e radiografia. Quatro pinturas com superfícies que apresentaram caracter-ísticas visuais associadas a tintas alquídicas, esmaltes ou caseiras se destacaram no grupo e são o tema desse artigo.Análises de pigmentos e meios ligantes indicaram a possibilidade de uso de tintas artísticas não tradicionais, masnão necessariamente caseiras, alquídicas ou esmaltes. A criatividade infinita de Picasso se refletiu na natureza exper-imental do seu trabalho com os materiais. Especificamente, a sua manipulação e alteração do meio em óleo, queimpactou diretamente a aparência e as propriedades de manuseio da tinta, devem ser levadas em conta. Finalmente,os resultados desse estudo ilustram a dificuldade na identificação de tintas para casas, barcos, ou outro material deuso não tradicional pelos artistas através apenas do exame visual e os desafios da sua caracterização analítica. Esseestudo mostrou a presença de materiais artísticos tradicionais do período, mas definitivamente não identificou mar-cadores químicos de tintas caseiras ou outros materiais não tradicionais.

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