Barium nitrate is the most commonly used oxidizer to make green fireworks.
Barium nitrate tends to get hard over time due to absorption of moisture. This granular material and any hardened barium nitrate can be quickly milled to a very fine powder before use with either a coffee/blade mill or a ball mill.
Although they are not interchangeable with barium nitrate, other green coloring agents are barium carbonate, the oxidizer barium chlorate, and the salt barium chloride. Boric acid is used in some liquid fire formulas.