The paint maker who uses large quantities of whiting will be discriminating in the selection of the material, and most likely find it to his advantage to carry several grades in stock, as he would hardly care to use common whiting for anything but the making of glaziers' putty. Whiting, even the better grades, is mostly slightly alkaline, and therefore unfit to be used in admixture with Prussian or Chinese blue and other colors affected by alkalies. The litmus paper test is sufficient to determine the presence of lime. Sometimes by-products of chemical works are offered as whiting that are very alkaline, and although much better in whiteness than the whitings prepared from chalk direct, are unfit for use in paint. Whiting is sometimes colored with iron rust, and while this will not be harmful in many instances, it will not serve its purpose when mixed with a pigment of pure whiteness.
Whiting should be tested for fineness in the same manner as barytes, i. e., diluted with spirits of turpentine and spread on a strip of glass with a spatula, comparing its texture with a standard of known quality. Its absence of color can be determined by placing the standard whiting side by side with the samples in small hillocks, wetting these with spirits of turpentine or making rubouts in bleached oil. The material is so low in price as compared with other pigments that it would hardly be possible to find anything to use in admixture, excepting perhaps the by-products of chemical works referred to above.