Cliffstone Paris white is sold in both lump and pulverized form and is largely used in potteries for making the white glaze with zinc oxide. For admixture with fine grades of paint and in the manufacture of paste driers for plate printing inks, etc., it is preferred to any-other grade, because when properly prepared it does not contain more than traces of grit. The method of its manufacture is similar to that of any other grade, with the exception that this and any other grade known as Paris white is levigated and floated. The crude lump chalk is broken up into small pieces in crushers, and the pieces of hard flint that occur in the chalk are removed as carefully as possible, as they play havoc with the mills, and the remainder of flinty substance not removed by picking is removed in the levigation and floating process, when the coarser particles settle to the bottom of the tanks and are known as tailings. The tailings are removed from the tank and disposed of before a new batch of the ground pulp is put in for levigation and floating, while the fine material is placed on steam drying pans in order to evaporate the water. In this process the chalk is ground with water, and the so-called bolted English cliffstone white, as well as the bolted American Paris white, are really the pulverized lumps, as they come from the drying apparatus, put through a disintegrator or pulverizing apparatus. The average English cliffstone Paris white will show one-quarter of 1 per cent of quartz or silica, while American Paris white will be found to contain from 1 to 2 per cent of that substance, the balance being calcium carbonate in the form of chalk.
Common or commercial whiting is obtained by powdering the crude chalk without paying any attention to picking out the flinty material or to levigation and floating. This grade of whiting will show as much as from 8 to 12 per cent of grit in the form of silica (sand). It is mostly used for making glaziers' putty.