Synthetic · Late 18th to late 19th century
Historically fatal toxicity
Contains arsenic; widely documented 19th-century cases of illness and death linked to wallpaper, clothing dye and paint made with these pigments.
Banned or heavily restricted for consumer use in most countries. Historical wallpaper/textile samples should be handled with appropriate care.
Scheele's green is a copper arsenite, and emerald (Schweinfurt or Paris) green is copper acetoarsenite — a copper arsenite with acetate built into its crystal. In both, copper ions absorb in the red, so the pigments look green; the arsenite framework and, for emerald green, its crystalline order give a cleaner, more brilliant colour than the copper greens that came before. Arsenic plays no part in the colour itself, only in the structure — and in the toxicity.
Carl Wilhelm Scheele described his green in 1775, and emerald green followed in 1814 from manufacturers at Schweinfurt, both made industrially by precipitating copper salts with arsenic compounds. Cheap and vivid, they spread far beyond painting into wallpaper, printed fabrics, artificial flowers, paper and even toys. Their use declined through the later 19th century as poisonings were documented; Scheele's green was out of use as a pigment by about 1900, although arsenical greens continued as insecticides.
Neither pigment is as stable as its brilliance suggests. Both darken where they meet sulfur — from polluted air or sulfide pigments such as cadmium yellow — forming dark copper sulfides. Recent synchrotron work on emerald green in oil found two routes: light oxidises arsenic at the paint surface, while very high humidity makes arsenic trioxide crystallise through the layer, and evidence from an Ensor painting pointed to the light-driven route. On wallpaper, damp and mould historically raised the separate problem of volatile arsenic compounds.
XRF finds copper and arsenic together, which is itself strongly suggestive; Raman and infrared spectroscopy then distinguish emerald green (with its acetate bands) from Scheele's green and from other copper greens, and microscopy shows emerald green's characteristic round, radiating particles. Because arsenic is readily detected, historic wallpapers and textiles are often screened with portable XRF before handling or display.
Viridian (a hydrated chromium oxide) and later phthalocyanine green took over the bright green role in paint, and synthetic organic pigments and dyes in wallpaper and textiles. Viridian is cooler and more transparent; phthalocyanine green is far stronger. Both are stable in light and with sulfur and carry no arsenic, so they give a similar brilliance without either the darkening or the hazard.
FactModerate evidence
Emerald green is a copper acetoarsenite that darkens in contact with sulfur compounds such as cadmium sulfide; it was replaced by viridian and phthalocyanine green.
FactStrong evidence
In emerald green oil paint, light drives surface oxidation of arsenic(III) to arsenic(V), while very high humidity instead favours crystallisation of arsenolite throughout the paint.
Caveat: Based largely on laboratory ageing plus one painting; pathways in other binders may differ.
FactModerate evidence
Scheele's green, invented in 1775, tends to blacken with sulfides and had fallen out of use as a pigment by 1900.
Source: Scheele's Green — Wikipedia