oxide white pigments are known as "zinc white" or depending upon the manufacturing process.

"Zinc White" (ZnO) by the French Process

In the manufacture of zinc white by the "French" process, metallic zinc is melted, evaporated and oxidized in the vapor state to zinc oxide with air. If the starting materials insufficiently pure, the zinc has to be purified by evaporation and condensation prior to the oxidation step. The size and shape of the zinc oxide crystals can be controlled by the oxidation conditions. After combustion the ZnO is precipitated from the ZnO/air mixture in settling chambers, in which classification of the zinc oxide particles takes place according to their size.

Zinc Oxide by the American Process

The raw materials for the manufacture of zinc oxide by the "American" process are roasted ores, concentrates of zinc ores or more recently zinc hydroxide or zinc carbonate from the processing of scrap. These are reduced with coal and directly reoxidized to ZnO in the same reaction chamber. The purity of the zinc oxide is normally somewhat inferior to that from the "French" process. Grades of various purities can be produced by fractionation.

Zinc Oxide by the Wet-Chemical Process

Zinc is precipitated from purified zinc salt solutions as the hydroxide, basic carbonate or carbonate, which is washed, filtered and dried. The pigment is obtained by subsequent calcination. Pigments suitable for particular applications can be obtained by varying the precipitation and calcination conditions. At low calcination temperatures particularly fine particles are produced, so-called transparent zinc oxide, which is actually the basic carbonate. Wet-chemically produced zinc oxides are particularly pure, since very pure zinc salt solutions can be produced.