Chemistry, Color, and Art - Journal of Chemical Education (ACS

Chemical Education Today

NCW 2001: Celebrating Chemistry and Art

Chemistry, Color, and Art by Mary Virginia Orna

Photo by Jerrold J. Jacobsen and Randall J. Wildman


Figure 1. Artists’ Pigments Used in Ancient Times: Verdigris [Cu(C2H3O2)2ⴢ2Cu(OH)2], Chinese Vermilion (HgS), and Venetian Red (red iron oxide, Fe2O3). All three are mentioned in Pliny the Elder’s 1st century work, Historia Naturalis.

Figure 2. A natural colorant, cochineal, is derived from the bodies of the female insect Coccus cacti, shown here. This material could be used either as a pigment when applied with a medium such as tempera or oil, or as a dye. It is most famous as the red dye used for 18th century British military uniforms, the famous “Redcoats.” The chemical identity of the red color is carminic acid.

JChemEd.chem.wisc.edu • Vol. 78 No. 10 October 2001 • Journal of Chemical Education


Sight is the primary sense and the first to be mentioned in antiquity. According to the Judeo-Christian religious tradition, God did not say “Let there be sound”, nor “Let there be odors”, but “Let there be light.” And so it was. The theme reappears in the bow of color across the sky signifying a covenant between God and humankind. As Michael Freemantle observed in his February 26, 2001, article in the Chemical and Figure 3. An array of modern pigments first manufactured and used in the 20th century. Artists now use many synthetic pigments such as these because they are stable, have uniform Engineering News, “color is the most properties, and are widely available. Top row, from left: cobalt silicate blue; cobalt violet phosvisual, pervasive example of the phate; zirconium vanadium blue zircon; cobalt titanate green spinel; titanium vanadium importance of chemistry to our lives” antimony gray rutile. Bottom row, from left: nickel antimony titanium yellow rutile; zinc ferrite (p 50). The purpose of this article is brown spinel; cadmium orange (CdS × CdSe); cadmium light red (CdS × CdSe); cadmium to connect artists’ colors and all that dark red (CdS × CdSe). their uses imply to this theme. Pigments and artists’ colors came along quite a bit later in common use (1). From about the late 15th century up to than the moment of creation. Palettes for grinding and mixour own time, dozens more pigments were synthesized. The ing face powders and eye painting unearthed from Egypdates when most of these pigments entered the artists’ paltian tombs date back to only 6000 B.C.E. Egyptian Blue ette is well-known and documented (2), a fact that enables (copper tetrasilicate, CaCuSi 4 O 10 ) and vermilion both scientist and historian to determine whether pigments (mercury(II) sulfide) were among the earliest of the manupresent in certain works are historically correct or anomafactured pigments. In addition to these and the naturally lous. Some naturally-occurring coloring matter is also derived occurring iron and manganese earth pigments, the Egypfrom plants and animals, although their use by artists has been tians, by 3000 B.C.E., had succeeded in expanding the artlimited because of their instability. Two of the most famous ists’ palette to red lead (Pb3O4), malachite (basic copper carof these colorants are indigo and cochineal (Fig. 2). Since bonate), orpiment (arsenic trisulfide), charcoal (carbon), and the development of modern chemical industry, hundreds red madder (from the root of the perennial Rubia more pigments have become available for many industrial, tinctorum). Figure 1 shows three important pigments from household, manufacturing, and artistic uses (Fig. 3). times past: verdigris, a name used to designate several copRobert Feller (3) has listed four purposes for identifying per compounds including the normal acetate, the dibasic by scientific examination the pigments that artists used: obacetate, and several carbonates; vermilion, also called Chijective description of method, restoration, conservation, and nese Vermilion; red iron oxide, called Venetian Red some authentication. Although most such work centers on the first time after the 14th century, one of the earliest known and three objectives, it is the latter that has captured the imagimost widely used pigments. nation of the public. As time went on, other pigments were added (see Table When I first entered the field of pigment identification, 1). By 1300, the list stood at about three dozen pigments it was in order to understand an artist’s method and, with a

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Figure 4. Portrait of St. Mark, p 188, Glajor Gospel Book, UCLA Special Collections. Used with permission of Department of Special Collections, Charles E. Young Research Library, UCLA. (Image not available for electronic version.)

little bit of luck, to be able to distinguish among the hands of several artists by noting possible differences in their palettes. My work on the Glajor Gospel Book (4) involved sampling of microscopic particles taken from the spectrum of hues used by each of the five artists known to have contributed to this massive 14th century work. The results of the X-ray diffraction analysis and chemical microscopy indicated a distinct difference in the palettes used by the two different workshops to which the five artists belonged. For example, the individual we called the Evangelist Painter used azurite, 2CuCO3ⴢCu(OH)2, a commonly used blue pigment, in the portrait shown in Figure 4, whereas his assistant, whose work faces Figure 4 in the original manuscript, typically used good quality ultramarine as the blue pigment. Members of the second workshop consistently used poorer quality ultramarine in their work (5).

Figure 5. El Arcángel Gabriel. 18th centur y Ecuador bulto. Stapleton Collection, National Museum of American Histor y, Smithsonian Institution. Photograph by Donald Hurlbert, Smithsonian Institution Office of Imaging, Printing and Photographic Services. Used with permission.

While such analysis provides an objective description of the work, the knowledge gained can also lead to conservation and/or restoration. For example, analysis of numerous manuscripts of Armenian and Byzantine origin that date between the 10th and 13th centuries revealed the fact that the Armenian palette, with one exception, consisted of mineral pigments, while the Byzantine palette consisted largely of pigments of plant and animal origin (6). (The exception is madder, a red pigment composed mainly of alizarin and extracted from the root of the madder plant, Rubia tinctorum.) Since organic pigments are not lightfast, knowledge of the respective palettes dictated immediately how these manuscripts were to be conserved with respect to display and exposure to light. Chemical analysis can also lead to restoration of a work of art so that it can be viewed as the artist had originally intended. An example is the restoration of “St. Sebastian”

Table 1. Common Artists’ Pigments Used from Early Times Common Name

Chemical Identity

Starting Date

Comments

Charcoal

Elemental Carbon

Before 1300

Also called carbon black. Produced by dry distillation of wood in a closed vessel.

Cochineal

Carminic acid, a glucopyranose derivative of alizarin

First described in 1549, but possibly used at least from the conquest of Mexico in 1523

Made from the bodies of the female cactus insect, Coccus cacti

Egyptian Blue

Calcium copper tetrasilicate, CaCuSi4O10

IV Egyptian Dynasty, or before

Crystalline compound containing some glass impurity

Indigo

Indigotin, C16H10N2O2

From prehistoric times; probably the oldest colorant known

Derived from different plants of the genus Indigofera

Iron oxide, red

Fe2O3

From prehistoric times

In continuous use in all geographic regions and time periods.

Madder

Alizarin; 1,2-dihydroxyanthraquinone


Extracted from the ground root of the madder plant, Rubia tinctorum

Malachite

Basic copper carbonate, CuCO3ⴢCu(OH)2


Oldest known bright green pigment

Orpiment

Arsenic trisulfide, As2S3


Derives its name from a corruption of auripigmentum, meaning gold color

Red Lead

Lead tetroxide, Pb3O4

From antiquity

Bright scarlet pigment with good hiding power; also known as minium

Verdigris

Dibasic acetate of copper Cu(C2H3O2)2ⴢ2Cu(OH)2

From antiquity

Other copper compounds, including carbonates, are also called verdigris

Vermilion

Cinnabar, HgS

From antiquity

One of the oldest synthetic pigments known


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Figure 6. Workshop of Daniel Miguel Sánchez. José Luis Valentín, 1996, Puerto Rico bulto from the collection of Nitza and Paco Toste. Photograph by Donald Hurlbert, Smithsonian Institution Office of Imaging, Printing and Photographic Services. Used with permission.

by Tanzio da Varallo that was accomplished by conservation chemist Barbara H. Berrie at the National Gallery of Art (7). Berrie’s analysis showed that two layers of overpainting applied much later to this early 17th century work could be safely removed to reveal “a pulsating yellow color [and] the sensuous folds of…drapery as Tanzio originally painted it.” Closer to home, a recent exhibit, “Santos: Substance and Soul,” mounted by the Smithsonian Center for Materials Research and Education, (8) focuses on the scientific study of the techniques and materials used by artists steeped in the tradition of santo-making throughout the Hispanic Americas from the 17th through the 20th centuries. Figure 5 depicts a typical santo, an 18th century bulto, or sculpture, from Ecuador. The exhibit documents how analysis of these works of art by a wide variety of instrumentation familiar to most chemists—X-ray diffraction, X-ray fluorescence, ultraviolet, visible, infrared, and mass spectroscopy, chromatographic methods, and scanning electron microscopy—has provided information about the evolution of this art form in separate areas where local traditions of materials usage developed. For example, wood analysis showed how artists in Puerto Rico

Figure 7. “San Rafael,” bulto. José Armijo, Española, New Mexico, 1999. Collection of Taylor Museum, Colorado Springs Fine Arts Center, Colorado Springs, CO. Used with permission.

used not only wood from native trees but also recycled wood from various sources, including shipping crates (from the 17th century, when the santos began to be created, until the present time), whereas New Mexican artists working during this same period tended to confine themselves to the use of local woods. Pigment analysis showed that the Puerto Rican artists tended to use conventional oil paints, but New Mexican artists made their own paints from locally available materials. Figure 6 is a modern work showing a Puerto Rican santero in his workshop, possibly using colorants imported for his use. Figure 7, on the other hand, is a work by José Armijo, a practicing santero from Española, New Mexico, whose practice bears out the analytical conclusions of the Smithsonian Institution. In recent correspondence, Armijo indicated that with few exceptions he uses local materials listed in Table 2. Figure 7 shows a work created from the local New Mexican materials used by Armijo. Rarely does one have the opportunity to verify by analysis the materials that an artist deliberately chooses, but even so, some of the materials that Armijo uses almost defy analysis. While there is a limited number of possible chemical identi-

Table 2. Sources of Colors Used by New Mexican Santero, José Armijo Color

Source

Processing

Yellow Yellow Green

Chamisal bush Yellow ocher from stone Clay from Placitas, NM

Boil the leaves

Red Blue Blue

Clay from Questa, NM Azurite purchased locally Indigo purchased from a pigment supply house Cochineal beetles obtained locally Black walnuts gathered locally Chimney soot gathered locally Rabbit skin glue plus gypsum 1 part piñon sap; 5 parts ethanol 1 part marble dust; 1 part yellow ocher; 1 part red clay Pine, aspen, cottonwood root, jelutong wood

Purple Brown Black White Varnish Flesh Colors Woods

Grind smooth with a glass muller on a marble slab and strain through cheesecloth Processed like the green clay Processed like the clays Processed like the clays Processed like the clays Boil hulls for hours; strain through cheesecloth

Must remain in contact for one week


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NCW 2001: Celebrating Chemistry and Art Figure 8. The miniature shown is from the Archaic Mark, a purported 12th century Byzantine Gospel of Mark that was written in an archaic form of Greek. Analysis of the blue pigment in this manuscript indicated that it belonged to a more modern period, possibly even the 20th century. Used with permission of the Department of Special Collections, University of Chicago Library.

ties to red clay, which normally contains a high percentage of iron oxide, green clay can present problems. One might guess that a close relative would be terre-verte, a complex mixture of the minerals glauconite and celadonite. At least Table 2 can point the analyst in the right direction—ultimately with the triple goal of objective description of method, restoration, and conservation. For a more complete account of the

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results of the santos featured in the Smithsonian exhibit, please visit the Web site (8), http://www.si.edu/scmre/santos. Robert Feller’s fourth stated purpose for the scientific examination of works of art is authentication. I like to think of this activity as “de-authentication” since one is more likely to be able to prove that a certain object is a fake rather than genuine. Two examples illustrate how an analytical tool can work in favor of the insurance agent. In the first instance, I was involved with a project some years ago that eventually showed that a purported 12th century Byzantine manuscript, the “Archaic Mark,” shown in Figure 8, was more than likely a modern forgery. This work housed in the Special Collections at the University of Chicago was found by chemical microscopy to contain large amounts of Prussian blue, a pigment that was first synthesized in the 18th century (6, 9). Another method, among many, that has entrapped would-be forgers of ceramic pieces is thermoluminescence dating. All clay materials contain radioactive materials that emit energy as they decay and some of this energy gets trapped in the clay body. When the clay is fired, the energy is released and the clock is reset, so to speak, so that the age of the piece can be measured from the time of firing by its thermoluminescent output. This method was first applied successfully (10) to the identification of numerous forgeries found among the 6th millennium B.C.E. Haçilar pottery pieces from southeastern Turkey (Fig. 9). Many other methods have been applied to famous and not-so-famous works of art to determine their authenticity and origin and some of their stories have appeared in this Journal (11). Attention is so often focused on how chemistry can examine a work of art that we seldom allude to the fact that chemistry itself has been the subject of artists from at least the time of the later alchemists (15th century). Figures 10 and 11 are two delightful paintings from the Fisher Collection depicting alchemists in their laboratories. Now housed at the Chemical Heritage Foundation in Philadelphia, these works portray alchemists working as metallurgists, physicians, dentists, and pharmacists. Plans are now underway to study these paintings comprehensively from the outside in and from the inside out. From the outside in, they will be examined for the materials they contain and the methods by which they were produced with a view to maximizing their conservation and preservation; they will be examined from the inside out, that is, by their subject matter, by Lawrence Principe of The Johns Hopkins University so that we can learn more about the chemistry that went on at the time of the paintings’ origins. This short paper has given a quick overview of some of chemistry’s relationships to the practice of art. For more information please see several articles from this Journal on artist’s colors (12) and the delightfully informative book recently published by Heinrich Zollinger, a renowned Swiss dye chemist, who deals with color in all of its aspects and especially as it touches the world of art (13).

Journal of Chemical Education • Vol. 78 No. 10 October 2001 • JChemEd.chem.wisc.edu


Figure 9. Counterclockwise from right. Genuine anthropomorphic vessel, 6th millennium B.C.E,; fake “Haçilar” doubleheaded vessel; fake “Haçilar” figurine; fake “Haçilar” snake. © Copyright The British Museum. ((Image not available for electronic version.)

Figure 10 (above). The Alchemist. Mattheus van Hellemont (1623–1674). Photo by Will Brown, Fisher Collection, Chemical Heritage Foundation, Philadelphia, PA. Used with permission. Figure 11 (at right). The Medical Alchemist. Franz Christoph Janneck (1703–1761). Photo by Will Brown, Fisher Collection, Chemical Heritage Foundation, Philadelphia, PA. Used with permission.

Literature Cited 1. Orna, M. V.; Goodstein. M. Chemistry and Artists’ Colors; Union Press: Wallingford, CT, 1998; p 283. 2. Gettens, R. J.; Stout, G. L. Painting Materials: A Short Encyclopedia; Dover Publications: New York, 1966. 3. Feller, R. L., Ed.; Artists’ Pigments: A Handbook of their History and Characteristics, Vol. I (of three); National Gallery of Art: Washington, DC, 1986. 4. Mathews, T. F.; Sanjian, A. K. Armenian Gospel Iconography: The Tradition of the Glajor Gospel; Dumbarton Oaks Research Library and Collection: Washington, DC, 1991; pp 48–51 and 227–230. 5. Orna, M. V.; Mathews, T. F. Studies in Conservation 26, 1981, 57–72. 6. Orna, M. V.; Lang, P. L.; Katon, J. E.; Mathews, T. F.; Nelson, R. S. Applications of Infrared Microspectroscopy to Art Historical Questions about Medieval Manuscripts. In Archaeological Chemistry–IV; Allen, R. O., Ed.; American Chemical Society Advances in Chemistry Series 220, American Chemical Society: Washington, DC; pp 265–288. 7. Ember, L. Science in the Service of Art. Chemical and Engineering News (April 16, 2001), p 9. 8. Santos: Substance and Soul, Smithsonian Center for Materials Research and Education. http://www.si.edu/scmre/santos/ mainmenu.asp (accessed Aug 2001). 9. Orna, M. V. J. Chem. Educ. 1997, 74, 373–376. 10. Jones, Mark, Ed. Fake? The Art of Deception; The University of California Press: Berkeley and Los Angeles, 1990; p 286. 11. See for example the papers by Rogers, F. E. J. Chem. Educ. 1965, 42, 619 and J. Chem. Educ. 1972, 49, 418. 12. Orna, M. V. Chemistry and Artist’s Colors, Parts I, II, III. J. Chem. Educ. 1980, 57, 256–267. 13. Zollinger, H. Color: A Multidisciplinary Approach; Wiley-VCH: New York, 1999.

Mary Virginia Orna is a member of the Department of Chemistry, College of New Rochelle, New Rochelle, NY, 10805; [email protected]. JChemEd.chem.wisc.edu • Vol. 78 No. 10 October 2001 • Journal of Chemical Education

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Chemistry, Color, and Art - Journal of Chemical Education (ACS

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