Production of iron oxide pigments

Claim 1

A METHOD OF PRODUCING A CRYSTALLINE IRON OXIDE PIGMENT OF IMPROVED COLOR WHICH COMPRISES ADDING A WATER-SOLUBLE FERROUS SALT TO AN AQUEOUS SOLUTION CONTAINING AT LEAST 130% OF ITS STIOCHIOMETRIC EQUIVALENT OF AN ALKALI-FORMING METAL HYDROXIDE AT A TEMPERATURE BELOW 40* C. THEN OXIDIZING THE RESULTING SUSPENSION AT A TEMPERATURE BELOW 40* C. AND WITHIN A PERIOD OF TIME OF FROM ABOUT 15 MINUTES TO 30 HOURS UNTIL SUBSTANTIALLY ALL OF THE IRON CONTENT OF SAID SUSPENSION IS CONVERTED TO FERRIC STATE, THEREAFTER COATING THE RESULTING IRON OXIDE PIGMENT PARTICLES WITH FROM 5% TO ABOUT 40% OF THEIR WEIGHT OF AN ORGANIC LYOPHILIC COATING AGENT AS A SUBSTANTIALLY MONOMOLECULAR LAYER OF THE ORGANIC LYOPHILIC COATING AGENT, AND THEN CALCINING THE TREATED PIGMENT PARTICLES AT 200* C.-400* C. FOR A PERIOD OF TIME NOT GREATER THAN ABOUT 3 HOURS