(Also known as Paris green). Emerald green is an arsenic-based organic pigment (copper acetoarsenite). It became available commercially in 1814. Its brilliant color was a favorite of Post-Impressionist painters Vincent Van Gogh and Paul Gauguin. The pigment largely went of use in the early 20th century, as awareness of its lethal toxicity grew and less toxic alternatives became available. Web resource here.

Vincent van Gogh. Self-portait dedicated to Paul Gauguin. Oil on canvas. 1888. The Fogg Museum, Harvard Art Museums, Cambridge, MA.