, 2. The herein-described process for manufacturing lithopone of various grades and a by-product of sodium hydrosulfid, which consists in preparing separate solutions of zinc sulfate and barium sulfid, which solutions are mixed with each other and with that of sodium bisulfate, all in equivalent and calculated amounts to produce and precipitate the desired grade of lithopone and leave the so dium hydrosulfid in solution, substantially as described.
In 1970, Japanese scholars studied the phase diagram of iron oxide microcrystalline formation, which laid a theoretical foundation for the preparation method of iron oxide yellow crystal seed. According to the research results, iron yellow crystal seeds can be formed under acidic or alkaline conditions. Because iron yellow is a crystal structure, in order to crystallize into pigment particles, it must first form crystal nucleus and become crystal seed, and then the crystal nucleus grows into iron yellow. Otherwise, only thin and dim color paste can be obtained, which does not have pigment properties. Acid process can be divided into iron sheet process and drop addition process.