Paris green (copper(II) acetate triarsenite or copper(II) acetoarsenite) is an arsenic- and copper-containing pigment. It is an emerald-green crystalline powder that is also known as Mitis green, Schweinfurt green, Sattler green, emerald green, Vienna green, emperor green or mountain green. It is highly toxic and has thus also been used as a rodenticide and insecticide. Its formula is Cu(C2H3O2)2·3Cu(AsO2)2. It was manufactured in 1814 to be a pigment to make a vibrant green paint, and was used by many notable painters in the 19th century. The color of Paris green is said to range from a pale blue-green when very finely ground, to a deeper green when coarsely ground. Due to the presence of arsenic, the pigment is extremely toxic. In paintings, the color can degrade quickly.
Preparation and structure Paris green may be prepared by combining copper(II) acetate and arsenic trioxide. The structure was confirmed by X-ray crystallography.
History In 1814, Paris green was invented by paint manufacturers Wilhelm Sattler and Friedrich Russ, in Schweinfurt, Germany for the Wilhelm Dye and White Lead Company. They were attempting to produce a more stable pigment than Scheele's green, seeking to make a green that was less susceptible to darkening around sulfides. In 1822, the recipe for emerald green was published by Justus von Liebig and André Braconnot. In 1867, the pigment was named Paris green and was officially recognized as the first chemical insecticide in the world. Because of its arsenic content, the pigment was dangerous and toxic to manufacture, often resulting in factory poisonings. The production of Paris green exposed factory workers in pigment production facilities to hazardous airborne arsenic compounds, leading to frequent cases of both acute and chronic poisoning. Because the pigment was handled as a fine powder, workers were especially vulnerable to inhalation and long-term internal exposure. These health risks made Paris green one of the most dangerous industrial pigments of the era. At the time, emerald green was praised as a more durable and vibrant substitute for Scheele's green, even though it would later prove to degrade quickly and react with other manufactured paints.
Pigment
In paintings, the pigment produces a rich, dark green with an undertone of blue. In comparison, Scheele's green is more yellow, and therefore, more lime-green. Paris green became popular in the 19th century because of its brilliant color. It was also called emerald green because of its resemblance to the gemstone's deep color.
Permanence The pigment has a tendency to darken and turn brown. The issue was already apparent in the 19th century. In a 1888 study, watercolors with the pigment were shown to darken and turn brown when exposed to natural light and air. Experiments at the turn of the 20th century gave mixed results. Some found that the Paris green degraded slightly while other sources said the pigment was weatherproof. This discrepancy could be due to the fact that each experiment used a different brand of Paris green. Paris green in Descente des Vaches by Théodore Rousseau has changed significantly.
Related pigments Similar natural compounds are the minerals chalcophyllite Cu18Al2(AsO4)3(SO4)3(OH)27·36H2O, conichalcite CaCu(AsO4)(OH), cornubite Cu5(AsO4)2(OH)4·H2O, cornwallite Cu5(AsO4)2(OH)4·H2O, and liroconite Cu2Al(AsO4)(OH)4·4H2O. These minerals range in color from greenish blue to slightly yellowish green. Scheele's green is a chemically simpler, less brilliant, and less permanent, copper-arsenic pigment used for a rather short time before Paris green was first prepared, which was approximately 1814. It was popular as a wallpaper pigment and would degrade, with moisture and molds, to arsine gas. Paris green was used in wallpaper to some extent and may have degraded similarly. Both pigments were once used in printing ink formulations. The ancient Romans used one of them, possibly conichalcite, as a green pigment. The Paris green paint used by the Impressionists is said to have been composed of relatively coarse particles. Later, the chemical was produced with increasingly small grinds and without carefully removing impurities. Its permanence suffered. It is likely that it was ground more finely for use in watercolors and inks.
Historical uses
Painting Paris green was widely used by 19th-century artists. It is present in several paintings by Claude Monet and Paul Gauguin, who found its color difficult to replicate with natural materials.
Insecticide In 1867, farmers in Illinois and Indiana found that Paris green was effective against the Colorado potato beetle, an aggressive agricultural pest. Despite concerns regarding the safety of using arsenic compounds on food crops, Paris green became the preferred method for controlling the beetle. By the 1880s, Paris green had become the first widespread use of a chemical insecticide in the world. The widespread agricultural use of Paris green as an insecticide also contributed to long-term environmental contamination, as arsenic compounds accumulated in soil and water systems after repeated spraying on crops and orchards. The compound did not break down easily, allowing toxic residues to persist in treated environments. It was also used widely in the Americas to control the tobacco budworm, Heliothis virescens. To kill codling moth, it was mixed with lime and sprayed on fruit trees. Paris green was heavily sprayed by airplane in Italy, Sardinia, and Corsica during 1944 and in Italy in 1945 to control malaria. It was once used to kill rats in Parisian sewers, which is how it acquired its common name. However, the manufacturing of the insecticide caused many health complications for factory workers, and in certain cases was lethal.
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