THALLOUS OXIDE (Thallium (1) Oxide) has been used in the manufacturing of glass of a high coefficient of refraction for optical purposes (thallium flint glass) and for artificial gems. Thallium oxide is black in color and is the inorganic compound of Thallium and Oxygen. THALLOUS OXIDE compounds are typically insoluble in aqueous solutions (water) and extremely stable making them useful in ceramic structures as simple as producing clay bowls to advanced electronics (e.g. tablets) and in light weight structural components in aerospace and electrochemical applications such as fuel cells. THALLOUS OXIDE is toxic by ingestion. It has previously been used as rat poison and ant killer, but its use is prohibited since 1972.