Method for the manufacture of a lead chromate-containing pigment having a low acid soluble lead content

A process for producing a lead chromate-containing pigment having an acid soluble lead content expressed as PbO of less than 5% by weight of the pigment and consisting essentially of mixed crystals of lead chromate, lead molybdate and from 1 to 3% of lead sulfate, said process comprising:

• forming an aqueous suspension of a coprecipitate of lead chromate, lead molybdate and from 1 to 3% of lead sulfate by contacting under acid conditions in the presence of chloride ions and in the absence of a buffering agent an aqueous chrome solution containing chromate, molybdate and sulfate ions with an aqueous solution containing sufficient lead ions to provide an excess of 0.01 to 0.10 mole of lead ions per mole of chromate, molybdate and sulfate ions during the coprecipitation;
• adding to the suspension a coating amount of a silicon compound and a trivalent antimony compound and precipitating said compounds as a surface coating on said coprecipitate;
• adjusting the pH of the resulting suspension to below 7;
• and recovering the coated coprecipitate as a pigment.