Verona Earth.—One kind of terre verte (see [p. 134]), is known by this name because it is produced in the neighbourhood of Verona.
Victoria Green.—This is a fancy name for the Brunswick greens compounded from Prussian blue, and already described on [p. 114.]
Vienna Green.—The aceto-arsenite of copper described under the heading of emerald green ([see pp. 121-125]), is sometimes called by this name.
Zinc Green.—The pigments described under cobalt green (see [p. 119]), as often pass by the name of zinc greens, and in fact they contain much more zinc than cobalt.
A handsome but not permanent green may be made by combining zinc with iron instead of cobalt, in the form of a double cyanide. The process is as follows:—Finely powdered Prussian blue is stirred into a concentrated solution of chloride of zinc, and put by to allow the decomposition to take place. After some time, the precipitated ferro-zinc cyanide is thoroughly washed, and dried out of reach of the light.
CHAPTER VI.
REDS.
Though the red pigments are an important class, they are not numerous, and, with the exception of a few lakes, they are drawn from the mineral kingdom. The most useful are compounds of the several metals, iron, lead, and mercury.
Antimony Vermilion.—This useful pigment is prepared by several methods, as follows:—
(1) One of the earliest successful processes was that introduced by Mathieu Plessy, which gives a scarlet product. He obtains the pigment, a modified sulphide of antimony, by decomposition of hyposulphite of soda in the presence of chloride of antimony. The two solutions of hyposulphite of soda and chloride of antimony, each at 25° B., being prepared, the next step is to pour into a stoneware vessel 4 gals. of the antimony chloride solution, 6 gals. of water, and 10 gals. of soda hyposulphite solutions. The precipitate caused by the water is rapidly dissolved in the cold by the hyposulphite. The stoneware vessel is then placed in a hot water bath, and the temperature of the contents is thus gradually raised. At about 86° F. the precipitation of the sulphide commences, showing orange yellow at first, but becoming darker subsequently. When the temperature has reached 130° F., the vessel is removed from the water bath, and the deposition of the precipitate proceeds rapidly. The supernatant liquor is siphoned off, and the solid residue is washed first with water acidulated by adding to it one fifteenth of its bulk of hydrochloric acid, and then with clean water. Finally the residue is collected on a filter, and dried. It is exceedingly brilliant while wet, but loses a portion of its brightness when dried.
Provision must be made for disposing of the sulphurous oxide gas driven off during the process of manufacture.