Thermally developable materials such as thermographic and photothermographic materials include a co-precipitate comprising first and second organic silver salts, the first organic silver salt comprising a silver salt of a nitrogen-containing heterocyclic compound containing an imino group, and the second organic silver salt comprising a silver salt of a mercaptotriazole. The first organic silver salt can be used in the imaging process as a source of reducible silver ions, and the second organic silver salt can be a source of a toning agent. The co-precipitate can be prepared using double-jet precipitation techniques to provide an aqueous dispersion that can be used in imaging formulations.