Paris White.—Another name for the best brands of whiting, see below.
Permanent White.—This name is often bestowed upon baryta white (see [p. 170]), on account of its durability as compared with white lead.
Satin White.—There is a certain amount of confusion in the application of this term, for while it is sometimes referred to baryta white (p. 170), it is also a synonym for fine gypsum (see [p. 183]).
Spanish White.—The most carefully prepared samples of whiting (see below), are often known by this name.
Strontia White.—Though much less common than the closely similar sulphate of barium, the natural sulphate of strontium is equally suitable for employment as a pigment, and is prepared in exactly the same way as baryta white (see [p. 170]). The artificial product is also used. Both possess qualities remarkably akin to those of baryta white.
Terra Alba.—An old-fashioned name for levigated gypsum (see [p. 183]).
Whiting.—This material is simply prepared chalk. It should be soluble in hydrochloric acid with effervescence, leaving at the most but a small residue. Sometimes samples of whiting are found which are more or less alkaline or caustic in their properties. This is a serious defect for many purposes. It can be detected by treating the sample with water, and adding to the liquor a little phenolphthalein. If a brilliant red colour is obtained, caustic lime is present, and the sample should be rejected, if to be used for mixing with chromes or Brunswick greens, where a neutral product is required.
Chalk itself is too familiar to need any description beyond saying that it essentially consists of carbonate of lime, with always a small percentage of silica associated with it.
Its preparation consists in hand selection to exclude the silica which, occurs in the more pronounced form of flints, then grinding in several stages, levigation and drying. The levigation is effected by having a series of settling pits into which the ground material flows with water, and deposits according to its degree of fineness. The drying is performed in chambers provided either with pipes carrying steam or heated air, or by fires beneath the floor, and thoroughly ventilated so that the moist air can escape as fast as it is saturated. Finally the dried whiting is again ground very fine. The drying must be done with great care and at a low temperature, so as to ensure avoiding calcination, whereby the carbonate of lime is changed into oxide (quicklime).
Whiting is a permanent and useful pigment mixed with water in distempers, but is not applicable as an oil colour.