Victoria Red.—One of the fancy names for Derby red. ([See p. 145.])
CHAPTER VII.
WHITES.
In the whole range of pigments there is no more important class than those to be described in this chapter. Not only are the white pigments largely employed for the sake of their distinctive colour, but they are probably even more extensively applied as a basis of other pigments, both as an ingredient in the composition of the other coloured paints and for ground coats where the final coat is to be of a delicate shade. They are among the cheapest and most permanent pigments, and possess as a whole remarkably good covering powers.
Baryta White.—Barytes or sulphate of baryta, the most important of the salts of barium, is found native in large quantities, forming the species of mineral termed barites or barytes, and commonly known as heavy-spar, on account of its weight (sp. gr. from 4·3 to 4·7). It is found in Derbyshire and Shropshire, and often occurs in fine tabular crystals. The massive variety found in the mountain limestone of the above counties is sometimes called “cawk”; it is more frequently found in white or reddish-white masses. In Saxony it occurs as the mineral stangen-spath, in a columnar form; and at Bologna, a nodular variety is found, called Bologna stone, which is notable for its phosphorescent powers when heated.
The pure salt may be prepared artificially for use as a pigment, by adding dilute sulphuric acid to a solution of chloride of baryta, when a white precipitate is formed; this is well washed and dried. It is a heavy, white powder, insoluble in water and nearly insoluble in all other menstrua. It may also be prepared by heating the native mineral, grinding it to powder, and well washing it, first in dilute sulphuric acid, in order to remove any traces of iron, and afterwards in water; the white powder is afterwards thoroughly dried. This process is employed at several works in the neighbourhood of Matlock Bath, in Derbyshire, but much larger quantities could be produced in different parts of the country if the demand for the article rendered its production more profitable. The principal use of sulphate of baryta is to adulterate white lead, and to form the pigment known as blanc fixe, or permanent white. For these purposes, the native mineral, ground and washed as described above, is commonly employed.
Improvements in machinery and in the process of treating natural barytes have overcome many of the objections which formerly existed to its utilisation, and considerable attention is now being given to the localities in the United States where it is found. The mineral, in order to be available for the uses to which it is put, must be fairly free from quartz grains, the stain of iron rust, and other impurities. If the barytes is stained to any extent, it is practically valueless, as a good white colour is essential to its usefulness. Quartz grains or other hard substances with which it is apt to be associated injure the machinery in grinding. The purest barytes so far produced in America comes from Missouri, though a very fair grade is now being mined in considerable quantities in Virginia.
The returns from all producers of crude varieties show a product in the United States, for 1889, of 21,640 short tons, valued at 106,313 dols., against 20,000 short tons in 1888, valued, approximately, at 110,000 dols. The product was limited to four States, as shown in the following table:—
| Short tons. | Value. | ||
| Illinois | 200 | $1,300 | |
| Missouri | 7,558 | 32,715 | |
| North Carolina | 3,000 | 15,000 | |
| Virginia | 10,702 | 57,298 | |
| Total | 21,460 | $106,313 |
Blanc Fixe.—This name is given to baryta white when it has been artificially prepared by adding sulphuric acid to a solution of chloride of barium. ([See p. 170.])