Barium carbonate
From PyroGuide
Formula: BaCO3
Synonyms: Barium monocarbonate, Carbonic acid barium salt
Description: Barium carbonate is used both in white and green color compositions. When chlorine donors are present in a composition a green color will result from the formation of BaCl+ in the flame. Without chlorine donors BaO will be formed which emits white light. Barium carbonate is convenient to use in chlorate based color compositions since it will neutralize residual acid which reduces the risk of spontaneous ignition.
Hazards: Most barium compounds are very poisonous, especially the more soluble barium compounds such as the chlorate and nitrate. A dust mask should be worn at all times when working with barium carbonate. Unlike its soluble cousins which can be easily washed from the hands with lots of water the carbonate is not so easily removed and care to remove the powder from under finger nails is important before eating etc. Barium carbonate is soluble in stomach acid, and therefore a poison by ingestion.
Sources: Barium carbonate is cheaply available in kilogram quantities from ceramic supply shops. However, this material is often contaminated with small amounts of barium sulfide that are left over from the production process. Therefore, ceramics grade barium carbonate should never be used in mixtures incompatible with sulfides such as chlorate based mixtures. Barium carbonate is not easily made at home.