Brandi Lee MacDonald
Artists’ pigments have long been a point of interest for researchers in cultural heritage. In the 1960s, Gettens and Plesters described the need for a handbook of painting materials that could serve the interests of chemists, conservators, curators, and collectors in the field of art.[i] Their efforts resulted in a series of volumes dedicated to the description of pigments by experts from around the world. That series, and others like it, are excellent sources of information on the extensive historical documentation of pigment history. This essay reviews a selection of commonly used artists’ pigments, and while not intended to be an exhaustive list of all pigments and their histories, our scope includes those materials we have identified as having been used to create the works included in this exhibition. The purpose of technical research on artists’ materials lies in the information it can reveal about which pigments the painters chose to use, their technique, and their process of mixing and layering paints. Data on the chemical composition of pigments are also used by conservators and conservation scientists for determining strategies for the restoration, preservation, and handling of works of art. Artists’ pigments fall within one of two broad categories: inorganic or organic. Inorganic pigments are derived primarily from mineral origins and have an extensive history of human use. Some of the first mineral pigments used by humans include red, purple, orange, and yellow iron oxides; kaolin clays; charcoal; and manganese dioxide; the earliest documented use of these include rock art sites across the globe.[ii] Organic pigments are generally carbon based, and their vivid colours are often derived from plant or animal origins. They are made using methods such as pulverizing insect husks, or by drying and grinding plant roots, and some examples include carmine yellow, indigo blue, and madder red. While the artists did employ both inorganic and organic pigments to create the works studied for The Unvarnished Truth: Exploring the Material History of Paintings, this survey focuses specifically on the mineral pigments used to highlight some of their unique histories.
Early and Modern Pigments: Development and Manufacture
For centuries before the Industrial Revolution, pigments were sourced, produced, and prepared on a local, small-scale basis, or imported from afar through extensive trade networks. A handful of pigment manufacturers and importers existed, such as the East India Company, which provided raw materials such as lapis lazuli from Afghanistan or vermilion from China. During the eighteenth century, however, pigment manufacturing became a widespread industry across Europe, giving rise to a range of new, synthetically prepared materials becoming readily available to painters. This transition resulted in some pigments, whose raw materials were easier to acquire, being more economically viable to manufacture, thus reducing cost; they were also safer to handle.[iii] In some circumstances, these newer synthetic materials were created to mimic and replace existing pigments that were expensive to import or process, were in short supply, or were difficult to access. For example, lapis lazuli was ground to create the vibrant blue pigment ultramarine, popular in use during the Renaissance and Baroque periods. In the 1820s, a synthetic replacement, sometimes referred to as French ultramarine, was produced by heating and grinding components including clay, sodium, sulphur, and charcoal. For many pigments produced after the late 1700s, their histories are typically well defined. It is possible to trace back through a timeline of manufacture the dates and locations of their production, if they were available to artists, and where other notable uses of the same paints are present. In some circumstances, the pigments themselves can be used as temporal markers, and in combination with other lines of evidence can be used for the attribution (sometimes referred to as authentication) of works of art. The proliferation of pigment manufacture in the eighteenth century changed the landscape of availability and accessibility to artists’ materials at an unprecedented rate.
Earth pigments are primarily a group of iron and manganese oxides, as well as clays, ranging in colours from red to brown, yellow, orange, black, and white.[iv] They are known commercially by names such as ochre, umber, sienna, and green earth, and are some of the oldest pigments used in human history. Iron oxides (Fe2O3, FeO[OH]×nH2O), which are the foundation of ochres and umbers, are typically formed through the weathering of iron-bearing rocks. Umbers (Fe2O3+MnO2) are manganese-rich deposits of a similar form, and are often more black or violet in hue. Geologic sources of iron oxides are located on virtually every continent of the globe, however their quality and suitability for use as pigment is variable.[v] Historically, iron oxides have been some of the most inexpensive and longest-lasting pigments available to artists, and their presence in most works of art is ubiquitous. For most of the history of their use, earth pigments were used straight from the geologic source by grinding and mixing mineral ores; however, in the late nineteenth to early twentieth centuries, they were manufactured synthetically by oxidizing metallic iron via aqueous precipitation. Iron oxides were used in almost all of the paintings studied in The Unvarnished Truth, and examples from the old masters include a work in the manner of Tintoretto, and works attributed to Adriaen Brouwer, and Jan Gossaert. Figure 1 shows the use of earth pigments on Brouwer’s The Drinker / The Bitter Draught.
Lead and Chalk Whites
White pigments are perhaps one of the most significant materials used by artists as they were often employed both as a ground underneath the presentation layer and as an admixture to modify other hues. The ground layer is an important component of a painting’s composition as it primes the canvas or board for the application and buildup of pigment. White pigment is found in virtually every European oil painting and occurs primarily in two forms: lead white and chalk white. Lead white (2PbCO3×Pb[OH]2) is one of the oldest of all synthetically produced pigments,[vi] and written records describe its preparation during the Greek and Roman Empires, and in China.[vii] Chalk white occurs in three primary forms: chalk (CaCO3), anhydrite (CaSO4), and gypsum (CaSO4×2H2O), a hydrated form of anhydrite. Chalk is derived from limestone, which is composed of microscopic fossils, while gypsum and anhydrite are evaporite minerals associated with sedimentary geologic deposits.[viii] Lead and chalk whites were often mixed together to produce the imprimatura, or underpainting, creating the base upon which other pigments were applied. In the nineteenth century, lead and chalk whites continued to be used, but they were often mixed with kaolin (Al2Si2O5[OH]4), barytes (BaSO4), and zinc white (ZnO).
We identified lead and chalk whites in most of the paintings in this study. Using X-ray diffraction (XRD) and scanning electron microscopy (SEM-EDS) (described in greater detail in the essay “The Analysis of Inorganic Pigments Using Spectrometric Techniques” in this volume) on a tiny paint flake removed from the edge of a portrait of a man (Cat. #) in the manner of Tintoretto, we identified a mixture of lead, anhydrite, and gypsum minerals during our investigation of the faux frame, a built-up layer of pigments in the corners of the work (Fig. 2).
Cobalt blue (CoO×Al2O3) is derived from the heating of cobalt ore and aluminum oxide minerals. As an oil paint, it is often presented as a soft, cool light-blue pigment, commonly used for skies in landscapes. Historical records indicate that geologic sources of cobalt ore were located in the Saxony region of Germany as well as in Hungary, Burma, and Sweden.[ix] It was used for millennia to colour glass and for pottery glaze, and was employed extensively as an ingredient in Roman glassware manufacture. However, it was not isolated as a painter’s pigment until 1803–04 by Louis Jacques Thénard, at which point it was rapidly commercialized.[x] It dries slowly, but is stable to light, heat, chemical agents, and atmospheric chemical pollutants. It was used widely in European easel paintings, and using X-ray fluorescence we identified it in the section shown in Figure 3 in Untitled, A Frozen Waterway with Villagers Playing Kolf and Skating and a Horsedrawn Sleigh (Cat. X), attributed to Aert van der Neer.
Vermilion is the name given to the pigment derived from mercuric sulphide (HgS), also known as cinnabar. It has been used for millennia, and evidence shows it was used in eastern Asia, in the lands that made up the Greek and Roman Empires, and in areas of pre-European-contact North and South America. The pigment occurs geologically in many areas of the world, most notably in Russia, China, Germany, Italy, Croatia, Peru, Mexico, and in the American states of Texas and California.[xi] In seventeenth-century Europe, Amsterdam was the primary location for dry-processing vermilion until the advent of wet-processing in the mid- to late nineteenth century.[xii] Wet-processing involved the heating of vermilion ore in a solution of ammonium or potassium sulphide, which was more cost-effective than the dry-processing technique. Vermilion is still produced and used in Germany and England to this day. Vermilion was identified to some extent in every one of the paintings included in this study. Figure 4 shows the area of the Alexander Rodchenko work where vermilion, the only mineral pigment identifiable from the piece, was located via X-ray fluorescence.
Azurite and Copper Greens
Azurite is a green-blue pigment composed of copper carbonate [2CuCO3×Cu(OH)2], and the group of associated copper greens includes variants such as emerald green [Cu(CH3COO)2·3Cu(AsO2)2], malachite [CuCO3·Cu(OH)2], and verdigris [Cu(CH3COO)2·nCu(OH)2]. Azurite is often found mixed with yellows to create blues and greens, and red lakes to create violet. Its synthetic counterpart, known as blue verditer, is almost chemically identical, and is produced by adding calcium carbonate to copper sulphate. The raw mineral azurite is found in many parts of the world, including Hungary, France, and Sardinia, and is historically known to have been used extensively in Egypt, eastern China, and Japan, as well as by pre-European-contact indigenous populations in central America. It has been described as one of the most important pigments used during the Middle Ages, the Renaissance, and later.[xiii] Using a combination of XRD and SEM-EDS, we identified azurite in the portrait in the manner of Peter Paul Rubens (Fig. 5). The pigment is known to have long-term discolouration and stability issues as it often turns to malachite over time, or darkens in the presence of sulphur fumes.
Chrome and Zinc: Modern Yellows, Blues, and Greens
A group of pigments synonymous with the modern age of pigment manufacture is derived from chrome- and zinc-rich minerals. Chrome oxides (chrome oxide, Cr2O3, and hydrated chromium oxide, Cr2O3 ×2H2O) produce green and green-blue pigments, ranging from dull to vibrant,[xiv] while another rarer occurrence, chromblaugrün is a richer blue (Cr2O3·CoO·Al2O3). These were introduced to artists’ palettes around the first half of the nineteenth century, and were known by names such as viridian, Guignet’s green, and Scheele’s green. Chrome-derived greens were known to have been used by Van Gogh during the late 1880s,[xv] and in our examination of Untitled, Still Life: Ginger Pot and Onions using X-ray fluorescence, we identified chrome-derived green in the brighter area of the jar, indicated in Figure 6. Other green areas around the jar that are duller in appearance are copper-derived greens.
Another group of chrome-, zinc-, and lead-based minerals are used to create yellow pigments, known commercially as chrome yellow or lemon yellow [PbCrO4 or, PbCrO4×PbSO4], or zinc yellow (K2O·4ZnCrO4·3H2O).[xvi] Chrome yellow was first produced in France in 1797 by Louis Vauquelin, but widespread production and use did not begin until the second quarter of the nineteenth century in France and the United States. It was originally extracted from the mineral crocoite (PbCr4O), but new methods of production, such as the precipitation of chromite (FeO·Cr2O3), created the potential for increased production. Zinc yellow, while chemically different from the chrome greens, was often used in combination with them. It was first synthesized in 1800, however it was not used extensively until 1850.[xvii] In our analysis of Murnau Landscape with Three Haystacks by Alexej von Jawlensky (Cat. #), we noted the presence of zinc—which could be associated with zinc yellow or zinc white—in many areas of the piece. This is discussed in greater detail in the essay “The Analysis of Inorganic Pigments Using Spectrometric Techniques” in this volume. Further investigation using chemical analytical techniques, such as X-ray diffraction of a removed paint sample, would verify this.
Artists’ pigments are an important source of information, and their study and documentation can reveal much, not only about artists, their techniques, and decision-making but also about broader historical and socioeconomic circumstances related to pigment manufacture that played out over time. Typically, a combination of expertise in technical art history and methodologies for chemical analysis are needed to achieve this end. The development and enhancement of new and existing technologies, such as macro X-ray fluorescence, X-ray diffraction, and scanning electron microscopy, have enabled researchers to discover previously unknown characteristics of pigments and to add to the records of historical literature on recipes, treatises on paintings, and manuscript sources related to painting technologies and practices. The essay “The Analysis of Inorganic Pigments Using Spectrometric Techniques” in this volume delves deeper into the scientific investigation of pigments, describing their chemistry, and the qualitative and quantitative methods and techniques for their analysis.
[i] Richard Buck, “Identification of the Materials of Paintings,” Studies in Conservation 11, no. 2 (1966): 52–3.
[ii] H. Valladas, J. Clottes, J.-M. Geneste, M. A. Garcia, M. Arnold, H. Cachier, and N. Tisnérat-Laborde, “Palaeolithic Paintings: Evolution of Prehistoric Cave Art,” Nature 413 (2001): 479.
[iii] R. D. Harley, Artists’ Pigments c. 1600–1835 (London: Butterworth Scientific, 1982), 58–9.
[iv] Brandi Lee MacDonald, R. G. V. Hancock, Aubrey Cannon, and Alice Pidruczny, “Geochemical Characterization of Ochre from Central Coastal British Columbia, Canada,” Journal of Archaeological Science 38 (2011): 3620–30.
[v] B. L. MacDonald, R. G. V. Hancock, A. Cannon, F. McNeill, R. Reimer, and A. Pidruczny, “Elemental Analysis of Ochre Outcrops in Southern British Columbia, Canada,” Archaeometry 55, no. 6 (2013): 1020–33.
[vi] “Lead White,” CAMEO: Conservation and Art Materials Encyclopedia, (Boston: Museum of Fine Arts), last modified, January 21, 2014, http://cameo.mfa.org/wiki/Lead_white.
[vii] R. J. Gettens, H. Kühn, and W. T. Chase, “Lead White,” in Artists’ Pigments: A Handbook of their History and Characteristics, vol. 2, ed. A. Roy (Washington, DC: National Gallery of Art, 1993), 67–81.
[viii] N. Eastaugh, V. Walsh, T. Chaplin, and R. Siddall, ed. Pigment Compendium: A Dictionary and Optical Microscopy of Historical Pigments (Boston: Elsevier, Butterworth-Heineman, 2004).
[ix] A. Roy, “Cobalt Blue,” in Artists’ Pigments: A Handbook of their History and Characteristics, ed. B. Berrie, vol. 4 (Washington, DC: National Gallery of Art, 2007), 151–77.
[x] Cobalt Blue,” CAMEO: Conservation and Art Materials Encyclopedia, (Boston: Museum of Fine Arts), last modified, January 13, 2014, http://cameo.mfa.org/wiki/Cobalt_blue.
[xi] R. J. Gettens, R. L. Feller, and W. T. Chase, “Vermillon and Cinnabar,” in Artists’ Pigments: A Handbook of their History and Characteristics, vol 2, ed. A. Roy (Washington, DC: National Gallery of Art, 1993), 159–82.
[xii] “Vermillion,” CAMEO: Conservation and Art Materials Encyclopedia, (Boston: Museum of Fine Arts), last modified, August, 1, 2013, http://cameo.mfa.org/wiki/Vermilion.
[xiii] R. J. Gettens and E. W. Fitzhugh, “Azurite and Blue Verditer,” in Artists’ Pigments: A Handbook of their History and Characteristics, vol. 2, ed. A. Roy (Washington, DC: National Gallery of Art, 1993), 23–33.
[xiv] “Viridian,” CAMEO: Conservation and Art Materials Encyclopedia, (Boston: Museum of Fine Arts), last modified, July, 24, 2013, http://cameo.mfa.org/wiki/Viridian.
[xv] R. Newman, “Chromium Oxide Greens,” in Artists’ Pigments: A Handbook of their History and Characteristics, vol. 3, ed. E. W. Fitzhugh (Washington, DC: National Gallery of Art, 1997), 273–90.
[xvi] “Chrome Yellow,” CAMEO: Conservation and Art Materials Encyclopedia, (Boston: Museum of Fine Arts), last modified, January, 13, 2014, http://cameo.mfa.org/wiki/Chrome_yellow.
[xvii] H. Kühn and M. Curran, “Chrome Yellow and Other Chromate Pigments,” in Artists’ Pigments: A Handbook of their History and Characteristics, vol. 1, ed. R. Feller (Washington, DC: National Gallery of Art, 1986), 187–217.