StudioMara - History of Pigments

ARTISTS' PIGMENTS 1780-1880: HISTORY AND USES

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The nineteenth century was more important than any other in the development of artists' colors was. It was an outgrowth of the flourishing field of chemistry that began in the eighteenth century. Chemists and colormakers began working side by side to develop new formulas for pigment production. Totally synthetic pigments were produced for the first time. The discovery of previously unidentified minerals opened up a range of brilliant and permanent pigments the likes of which had never been known before.

The artists' palette was lacking in yellows and greens more than any other hue by the end of the eighteenth century. A new hue was also needed to replace the costly ultramarine, genuine. The discovery of Cobalt, zinc, chrome and metallic cadmium early in the century made the necessary additions possible.

In the later part of the century, improvements were made to some of the ancient dye colors and known minerals were developed for artists' use. Zinc, for example, had been known since antiquity when it was melted with copper to form brass. Many pigments, including zinc, are found in the medical profession. It was employed then, as it is today, as a medicinal ointment (Paint and Painting [1982], 19).

The first part of this discussion of nineteenth century pigments will describe the most notable ones in the order that they were discovered. It will be concerned with the following issues:

1. The circumstances of their discovery and means of fabrication will be analyzed. Their method of manufacture falls into two groups. The 'wet process,' used for pigments such as Aureolin, chrome colors and emerald green, involves substances that are oxidized with water or mixed with chemicals and usually heated. Their pigment particles are generally crystalline in structure and tend to be less permanent than 'dry process' pigments. The latter, such as artificial ultramarine, cadmium and cobalt colors are generally made in a furnace with extreme heat (Blockx 1910, 53).

2. The characteristics of each pigment will be discussed. Pigments are inherently either opaque or transparent. The former would be more appropriate as a tinting or body color; the latter being better suited for a glaze color. Some pigments are lightfast and unchanged by impure air. In the nineteenth century there was a particularly high level of sulfur in the air that damages certain pigments. The cause of sulfur-bearing air was due to the use of coal and gas for heat and light in the artists' studio as well as in the gallery. Sulfur is a by-product of the combustion of coal and gas (Field 1885, 88).

3. The opinions of important colormakers and writers will be mentioned. In particular, George Field (1777?-1854), British colormaker and Jacques Blockx (1844-1913), Belgian colormaker will be mentioned as they tested and sold the pigments under discussion.

4. The identification of the pigments, both microscopically and chemically will be analyzed. This information becomes important when the palettes of artists are not known and is useful for dating paintings on the basis of pigment availability. The process involves the removal of a very small fragment of dried paint from the painting. It is first examined under the microscope and then subjected to a variety of chemicals. By comparing the results to known pigment samples, identification can be made.

The latter part of this paper will analyze the palettes of some of the key nineteenth century painters. It will begin by discussing developments in the artists' colorman's trade, which were responsible for bringing the new pigments to the marketplace.

The middle of the century was marked by the publication of books on color theory and test results on the new pigments. The invention of the collapsible metal tube brought the artist out of the studio and into the landscape. The beginning of Impressionism was a result of these developments. Painting was revolutionized in the third quarter of the nineteenth century. It would have been quite a different story had the artists not capitalized on all that was happening.

The first modern, artificially manufactured color was Prussian blue. It was made by the colormaker Diesbach of Berlin in about 1704. Diesbach accidentally formed the blue pigment when experimenting with the oxidation of iron (Gettens and Stout 1966, 149-151). The pigment was available to artists by 1724 (Mayer 1970, 64).

Fifty years passed before the Swedish chemist Carl Wilhelm Scheele discovered the next new pigment in 1775. Scheele developed a green pigment while investigating the nature of arsenic. Scheele's green, as it would be known, was the first to virtually replace the ancient copper carbonate greens by the end of the nineteenth century.

Scheele's green was copper arsenate (CuHAs03); the first pigment to contain arsenic. Scheele mentioned it in 1777, in a letter to another scientist. In this letter Scheele discussed the highly toxic nature of the pigment. He also sought to protect himself from anyone else claiming the discovery. In 1778, the Stockholm Academy of Sciences published his detailed instructions for making it. First, potash and powdered arsenic sulfide (As203) were dissolved in water and heated. The alkaline solution that resulted was added, a little at a time because of foaming, to a warm solution of copper sulfate. When allowed to stand, the green pigment would settle out. The liquid was poured off and then the pigment was washed and dried on low heat (Harley 1970, 75-76).

The great exchange of scientific information at the end of the eighteenth century made Scheele's green widely known. It was described in 1795 in the Practical Treatise on Painting in Oil, London. In 1812, its method of manufacture and range of variations were patented in England (Harley 1970, 76). Its yellowish-green color faded rapidly and sulfur-bearing air and sulfide blackened it pigments (Gettens and Stout 1966, 155). However, Field and Laurie considered it superior to other copper greens for its brilliance and durability, such as it was. Field also mentioned that an olive green could be made by burning either verdigris or Scheele's green (Hartley 1970, 76).

Scheele's green can be identified under the microscope as small and large irregular-shaped green flakes that are slightly transparent (Gettens and Stout 1966, 155). Laurie suggests that it can be identified by comparing it to copper carbonate greens under the microscope. He also discussed one method for chemically identifying arsenic compounds with a stannous chloride test. A sample of verditer (a copper green), a known sample of Scheele's green and an unknown sample are placed on a glass slide. The samples are coated with collodion and immersed in a bath of stannous chloride dissolved in a strong hydrochloric acid. It is then heated to 60°C. The verditer will dissolve and the arsenic green will turn a brownish-black (Laurie 1914, 52).

A few years before he discovered his green, Scheele discovered a process for preparing compounds of sodium; lead oxychloride was a by-product. Although he published his findings for a new yellow pigment of lead oxychloride in 1775, he did not continue to develop it. Patent yellow, also known as Turner's yellow (PbC12. 5-7PbO) was patented by James Turner of England in February 1781, hence its name. Turner noted Scheele's discovery as applicable for, "a method of producing a yellow colour for painting in oil or water, making white lead, and of separating the mineral alkali from common salt, all to be performed in one single process" (Harley 1970, 91-92). The yellow pigment was made by grinding together, in water, two parts of lead (either red lead or litharge) and one part of sea salt. The mixture was allowed to stand for twenty-four hours. A caustic soda solution was poured off and the remaining white substance was heated (and dried) until it reached the desired shade of yellow.

Turner's patent did not prevent other manufacturers from copying his process. He sued one competitor and won the case on appeal in 1787. The case was published in books on patent law because it was won on a ruling that stated that if a patentee claimed to do several things by one process and one failed; the whole patent was void. In fact, Turner had listed several different names for lead and for the type of salt that could be used. Turner's competitor could not prove definitively that variations in the raw materials would not produce the pigment and Turner retained his patent.

A statute ordered by an Act of Parliament extended the time allowed to Turner as the sole manufacturer because competitors had taken his rightful income. It went on to state that Turner's yellow was superior and less costly than orpiment. It contributed to the National income of England and to the salt tax in that it was made from native raw materials.

Turner's yellow was widely used in England and regarded as durable and bright. It was sold at one shilling per watercolor cake in spite of a known tendency to blacken. Field claimed that it worked well in both oil and watercolor but noted its impermanence in sunlight.

In spite of the introduction of more permanent yellows in the nineteenth century, it was produced on a large scale. C. T. Kingzett, author of The History, Products and Processes of the Alkali Trade, 1877, recorded its production at a soda factory at Walker-upon-Tyne, England, where it was sold as Turner's Patent Yellow. At the Great Exhibition of 1851, an example of its use in oil was provided by the Washington Chemical Company of Washington, Durham, England (Harley 1970, 91-92).

Schweinfurt green or emerald green was developed in an attempt to improve Scheele's green. This copper aceto-arsenite (Cu(CH3COO)2.3Cu(AsO2)2) pigment was first produced commercially by the firm of Wilhelm Sattler at Schweinfurt, Germany in 1814 (Wehlte 1982, 131). Justus Von Liebig and Andre Bracconot separately published papers on its method of manufacture. Von Liebig's paper "Sur une couleur verte" was published in 1823 in Annales de chimie XXIII (pp. 412-3). Verdigris (or acetic acid) was dissolved in vinegar and warmed. A watery solution of white arsenic was added to it so that a dirty green solution was formed. To correct the color, fresh vinegar was added to dissolve the solution. The solution was then boiled and bright blue-green sediment was obtained. It was then separated from the liquid, washed and dried on low heat and ground in thirty- percent linseed oil. The pigment was considered a good drier (Harley 1970, 77).

Schweinfurt green had brilliance unlike any other copper green. Field considered it a more durable pigment than Scheele's green but it had the same tendency to blacken on exposure to sulfur-bearing air (Harley 1970, 77). Romanesque murals are known to contain the natural mineral emerald green and have held the color well. The old Masters, who used verdigris and copper greens due to a lack of more durable options, isolated the pigments in between coats of varnish that helped to alleviate changes. Schweinfurt green was also made more stable in a varnish medium (Doerner 1931, 83). It could not be mixed with sulfur-containing colors, such as cadmium yellow, vermilion or ultramarine blue because they acted chemically on it to produce a deep brown color (Laurie 1926, 93). Field considered its use to be limited as it was not a green that occurred in nature (Harley 1970, 77). The arsenic content made it extremely poisonous and it was blamed for deaths when employed as a wallpaper color (Pavey 1984, 24).

Microscopically, it appears as small rounded grains that are uniform in size making it readily distinguishable from Scheele's green. At high magnification, the grains are radial in structure and a dark spot can be seen in the center (Gettens and Stout 1966, 113). It can be identified chemically by the stannous chloride test described for Scheele's green and has the same reaction for arsenic. In potassium hydroxide, it turns into an ochre color and in weak sulfuric acid it dissolves and turns blue (Doerner 1934, 83).

Until the nineteenth century, the painter's palette was lacking in a permanent, bright yellow more than any other primary hue. In painting and illumination of antiquity, gold leaf often served to balance the palette. Orpiment, a pale, lemon yellow was extensively employed as well. It lacked brilliance and was not mixable with most other pigments. Therefore, Turner's yellow gained popularity very quickly. Another new yellow, Indian yellow, had the same rapid introduction. This research has not uncovered a known date of its introduction but Wehlte notes its appearance in the middle of the eighteenth century (Wehlte 1982, 95).