Scheele's green, also called Schloss green, is chemically a cupric hydrogen arsenite (also called copper arsenite or acidic copper arsenite), CuHAsO3. It is chemically related to Paris green. Scheele's green was invented in 1775 by Carl Wilhelm Scheele. By the end of the 19th century, it had virtually replaced the older green pigments based on copper carbonate. It is a yellowish-green pigment commonly used during the early to mid-19th century in paints as well as being directly incorporated into a variety of products as a colorant. It began to fall out of favor after the 1860s because of its toxicity and the instability of its color in the presence of sulfides and various chemical pollutants. The acutely toxic nature of Scheele's green as well as other arsenic-containing green pigments such as Paris green may have contributed to the sharp decline in the popularity of the color green in late Victorian society. By the dawn of the 20th century, Scheele's green had completely fallen out of use as a pigment but was still in use as an insecticide into the 1930s. At least two modern reproductions of Scheele's green hue with modern non-toxic pigments have been made, with similar but non-identical color coordinates: one with hex#3c7a18 (RGB 60, 122, 24) and another with hex#478800 (RGB 71, 136, 0). The latter is the more typically reported color coordinate for Scheele's green.
Preparation
The pigment was originally prepared by making a solution of sodium carbonate at a temperature of around 90 °C (194 °F), then slowly adding arsenious oxide, while constantly stirring until everything had dissolved. This produced a sodium arsenite solution. Added to a copper sulfate solution, it produced a green precipitate of effectively insoluble copper arsenite. After filtration the product was dried at about 43 °C (109 °F). To enhance the color, the salt was subsequently heated to 60–70 °C (140–158 °F). The intensity of the color depends on the copper : arsenic ratio, which in turn was affected by the ratio of the starting materials, as well as the temperature. It has been found that Scheele's green was composed of a variety of different compounds, including copper metaarsenite (CuO·As2O3), copper arsenite salt (CuHAsO3 and Cu(AsO3)2·3H2O)), neutral copper orthoarsenite (3CuO·As2O3·2H2O), copper arsenate (CuAsO2 and Cu(AsO2)2), and copper diarsenite (2CuO·As2O3·2H2O).
Uses Scheele's green was used to color wallpapers, paper furniture linings, and textiles used in clothing and bookbindings, along with paints, wax candles, and even some children's toys. Modern researchers, including the University of Delaware's Poison Book Project, have identified numerous 19th-century cloth-case bindings coloured with Scheele's green, and they advise handling such books with care because the pigment can flake off as toxic dust. Scheele's green is more brilliant and durable than the then-used copper carbonate pigments. However, because of its copper content it tends to fade and blacken when exposed to sulfides, whether in the form of atmospheric hydrogen sulfide or in pigment mixtures based on or containing sulfur. Emerald green, also known as Paris green, was developed later in an attempt to improve Scheele's green. It had the same tendency to blacken, but was more durable. Despite evidence of its high toxicity, Scheele's green was also used as a food dye for sweets such as green blancmange, a favorite of traders in 19th-century Greenock; this led to a long-standing Scottish prejudice against green sweets. While sources may conflict with each other, one source accounts that the color Scheele’s green was used on posters for the Siege and commune of Paris. These “posters range in date from 1869–1887." Scheele's green was used as an insecticide in the 1930s, together with Paris green.
Toxicity In the 19th century, the toxicity of arsenic compounds was not readily known. Nineteenth-century journals contained reports of children wasting away in bright green rooms, of ladies in green dresses swooning, and of newspaper printers being overcome by arsenic vapors. There is one example of acute poisoning of children attending a Christmas party where dyed candles were burned. Although some European nations started banning arsenic-containing pigments in the 1830s and 1840s, Scheele's green did not completely fall out of favor until the 1860s. Publicity associated with the 1861 death of 19-year-old Matilda Scheueur as a result of her job dusting artificial foliage with the pigment increased public awareness of the toxicity of Scheele's green. An article "Pretty Poison-Wreaths" described her repeated illness from arsenic poisoning leading to her death, and detailed autopsy findings of eyes and fingernails turned green from the pigment. By the 1890s the last brand of wallpaper using it ceased production.
Illness associated with arsenic containing wallpaper
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