Abstract: A fine, largely beta phase calcium pyrophosphate powder for, e.g., a diffuser coating for the interior surface of lamp envelopes. The powder is useful for electrostatic deposition of such coatings under varying conditions of environmental humidity. A process for the synthesis of the calcium pyrophosphate is also disclosed. Dibasic calcium orthophosphate (monetite) is dissolved in a dilute aqueous hydrochloric acid solution and spray-dried to form a calcium phosphate powder of spherically shaped hollow particles. The calcium phosphate powder is fired in air to convert the calcium phosphate powder to a spherical calcium pyrophosphate powder including the beta phase as a major component and the gamma phase as a minor component. For a diffuser coating, the poder is sonicated to fragment a portion of the hollow particles.