Copper (I) chloride
From PyroGuide
Formula: CuCl
Synonyms: Cuprous Chloride, Cuprous monochloride, Nantokite
Description: CuCl is a white or green powder, the green color comes from oxidized impurities. It is insoluble in water, but soluble in hydrochloric acid. It is almost never used in pyrotechnics.
Hazards: Toxicity: LD50: 140mg/kg
Synthesis: Method 1: Boil an aqueous solution of Copper (II) chloride together with powdered or granulated copper metal. The copper (I) chloride will form in the water as a green powder. Filter it and dry.
Method 2: Make a solution of Copper sulfate. Then add Sodium chloride and Potassium metabisulfite. When the reaction is finished you will see white Copper (I) chloride on the bottom of container. Then decant the supernatent solution to leave Copper (I) chloride. Wash it with Ethanol (water works well too) two or three times to obtain a purer product.
Method 3: Pure white Copper (I) chloride can be produced from red Copper (I) oxide (Cu2O)and a stochiometric quantity of Hydrochloric acid. This method also produces soluble Copper (II) chloride (CuCl2). Too much Hydrochloric acid will convert the CuCl to CuCl2. The two chlorides, if done well, can be separated by simple decantation. Wash with water then dry.
References
Wikipedia[1]
CopperColors blog[2]