Pigments for Decoration

Indigo Blue

is an ancient pigment of the na ture of a dye, obtained from herbaceous plants which grow in India and other hot countries, and is usually sold dry in the form of little knobs. In its color, qualities and appearance it somewhat resembles Prussian blue, but is very inferior to that pigment for oil painting. It is for water color purposes that indigo is valuable. It is one of the most useful pigments for distemper tints that we have, and is just as permanent in water as it is unreliable in oil—that is, if good and pure indigo is used. The price, however, prevents its use to any great extent in house painting, being about four times as expensive as French ultra marine.

Indigo is also obtained by an electrolytic process, which gives it in the purest form obtain able. The dried plants are steeped in water, which becomes yellow in color, and a current from copper electrodes is then made to pass through the liquid.

Prussian Blue

is made from the action of prussiate of potash upon iron, the cyanide of the potash uniting with the iron, producing the blue color. It is a blue of much beauty and strength, not quite so pure as ultramarine, possessing a slight tinge of green, which, however, makes it none the less useful and beautiful for the painter's use. Some writers on the subject credit Prussian blue with the property of fluctu ating—losing and gaining color—according to the preponderance of oxygen in the air, although under all ordinary conditions it is quite reliable for oil painting. It gives very fine tints of blue in admixture with white lead; added to black in small quantities, it makes that neutral appear still more black and intense; while its brilliancy and transparency make it very useful for glazing over gold and silver leaf—a process so much used at the present time in decorating modern relief wall-hangings. Some notion of the strength of Prussian blue as a staining pigment may be gathered from the fact that one-half ounce ground in oil would stain twenty pounds of white lead paint to a decided light blue. It is seldom used in water or distemper painting, as it does not show the same qualities of brilliancy and permanence as when used in oil. Its price is about that of good French ultramarine; it is always sold ground in oil or water, being too hard for the worker to grind or mix himself from its raw state.

Lime Blue, a cheap powder of somewhat similar color to ultramarine, comes next in order of usefulness, but far less pure and strong as a stainer. As its name implies, it is useful only for mixing with water preparations of chalk lime or whiting (carbonate of lime), and is much used by the paper-stainer for cheap goods. It is practically useless for oil paint.

Royal Blue is a finely-ground cobalt; that is, it is ground in a glass tinted with cobalt, which is disintegrated by plunging it while hot into cold water.

Ultramarine Blue is by far the purest and most costly of all pigments in our use and knowl edge, and has been known and used from the time of the first Pharaohs. Its name is derived from the Latin "ultra,"' beyond, and "mare," the sea; and by the ancient Greeks it was known as Armenian blue. The real color is made from a precious stone, which is, however, destroyed in the process. This stone, called lapis-lazuli, is of a beautiful azure color, marked with fine golden veins, and is obtained chiefly from Persia and Siberia.

A comparatively cheap form of so-called "ultramarine" is prepared artificially in a great number of qualities. It is always sold in the form of a fine powder. It is a most useful pig ment, possessing much purity and brilliancy, is permanent, and can be mixed with either oil or distemper paints.

Vandyke Brown is an earth, consisting of iron and bituminous coal. It is a deep rich brown, useful to a degree in pictures or in grain ing; with oil it is a bad drier. It is not a very permanent color, and is rather mischievous to other colors.

Chrome Yellow is made by mixing bichro mate of potash with acetate of lead, or, as it is commercially called, sugar-of-lead. It is also made commercially by staining whiting with the bichromate. This is done to give it a body; the lead is boiled in bichromate of potash. On the duration of time of the boiling, depends whether it is lemon, deep or middle chrome. Soda is also used in the above process to produce red chrome. It is easy to see that this color should not be used with zinc-white. Chrome tints look very rich with browns or purples, but chrome colors are fugitive.

Yellow and Orange Chromes are very often adulterated. In the pure state they consist of chromate of lead or chromate and sulphate of lead.