For most of art history there have been no reliable green pigments. The best for a long time was Malachite which tended to be variable in quality and permanence. Various colors made from plant extracts were very impermanent. In old master days the only reliable way of using green was from mixtures or glazing blue over yellow. Green Earth was rare and considered too weak to be of much use anyway. Starting in the late 18th century green pigments started to be discovered with regularity. Popular because of its beauty, Emerald Green was poisonous (and a favourite of Van Gogh). Virdian, discovered in 1838 and then Pthalo Green in 1938 finally provided artists with the perfect deep greens.