Copper carbonate (basic)
From PyroGuide
Formula: CuCO3.Cu(OH)2
Synonyms: Malachite
Description: A beautiful light blue to deeper blue powder, which sometimes is used as a pigment. Used as a blue flame colorant in low temperature class compositions of the potassium (per)chlorate base or in compositons of the ammonium perchlorate base. The resulting blue is weaker than that using Paris green or CuSO4.
Sources: Pyro suppliers, ceramic supply store (used for glazing, ceramic grade copper carbonate sometimes might contain acidic impurities left from production and should therefore be tested).
Synthesis: Method 1: Dissolve a soluble copper compound (Copper acetate, Copper (II) chloride, or Copper sulfate for example) in as little distilled water as possible. Make a seperate solution of Sodium carbonate or Sodium bicarbonate in as little distilled water as possible. Mix these two solutions slowly and Copper carbonate will precipitate out. (if you are using Sodium bicarbonate there will be a lot of fizzing) Filter, wash with distilled water, and allow to dry without heating it. (sunlight is OK)
Method 2: Add Copper hydroxide to Carbonic acid (tonic water) and Copper carbonate will precipitate out. Filter, wash with distilled water, and allow to dry without heating it. (sunlight is OK)
Hazard Symbols: Xn
References
Images from Keten used with permission. Thanks a lot!