Strontium carbonate
From PyroGuide
Formula: SrCO3
Description: White to pale pink powder. Strontium carbonate is used in combination with chlorine donors to produce red colors. It also acts as an acid neutraliser, for which reason it is prefered in chlorate based compositions (which may spontaneously ignite when traces of acid are present).
Hazards: Strontium carbonate is not particularly dangerous or toxic.
Sources: Strontium carbonate is cheaply available in kilogram quantities from ceramic supply shops. However, this material is often contaminated with small amounts of strontium sulfide which are left over from the production process. Therefore, ceramics grade strontium carbonate should never be used in mixtures incompatible with sulfides such as chlorate based mixtures. Strontium carbonate is not easily made at home.