is exposed to the action of carbonic acid and water, more or less of the zinc oxide is converted in time into zinc carbonate, which is more obviously crystalline and more bulky than the oxide ; therefore, such a paint would lose its hiding power, and increase in volume, causing motion in the dried paint. The remedy for the defects in zinc oxide is to combine it with other pigments that will improve it.

The varieties of zinc oxide sold are of two essential kinds: First, that from the oxidation of metallic zinc; second, that obtained from the sublimation of zinc ores. The former are more dense and better paint pigments than the latter. (Occluded gases.)

The particles of zinc oxide are "needle-formed," like snow. The objectionable features in oxide of zinc may be largely overcome  by  tempering  and  combining it