Copper acetoarsenite
From PyroGuide
Synonyms: Paris Green
Formula: Cu3As2O3Cu(C2H3O2) 2
Description: Copper acetoarsenite is a green powder which is used in blue color compositions. It can produce great blues but it is also very poisonous and is used less and less for that reason. Today alternatives are available that will produce deep blues with less poisonous and cheaper compounds.
Hazards: Copper acetoarsenite is very poisonous and should only be handled wearing a dust mask. Smoke from compositions containing this compound should not be inhaled. It is best to avoid the use of this compound altogether as several safer alternatives have become available in the past decades.
Sources: Copper acetoarsenite was used in the past as a pigment known as emerald green, kings green or vienna green. Nowadays it is no longer used and it is very hard to find a paint supplier that still has it. It can be prepared at home but extreme caution must be excercised since arsenic compounds are very poisonous. The following preparation originates from Shimizu: "300 g of copper sulphate is dissolved in 1000 ml water, to which 250 g of glacial acetic acid is added; This solution is named 'A'. Then 200 g of sodium carbonate and 200 g of arsenious acid (comment: note that this is an aqueous solution of arsenic-III-oxide, which is a strong poison) are added to 1000 ml water and boiled to form a solution, this is named 'B'. B is added little by little to A with constant stirring. Carbon dioxide gas is generated with active bubbling. When all the solution B has been added, it is boiled for about 30 minutes, when copper acetoarsenite appears gradually as green particles in the solution. The mother liquor is removed by vacuum filtration, and then green substance, copper acetoarsenite, is washed with water untill the sulphate ion dissapears; it is then dried. The yield is about 180 g."