PAINTS. A paint is composed of a pigment, which is a solid substance 7round to a fine powder. mixed with a liquid of such a nature that when spread in a thin film and exposed to the air it will turn into an adhesive and more or tough solid substance, thus cementing the particles of pigment to each other and to the coated surface. The pigments used in making are of various ori7ins and conqiosition:. but all are of such a nature as to have little or no chemical action on the liquid component. This liquid may he watery, like the solution of glue used in kalsomine. or an oil. like linseed oil: or it may he any kind of varnish. In all eases this liquid part of the paint is. while liquid, called the vehicle, and when dry the binder. To the mixture of pigment and vehicle there is usually added a drier and a or thinner. paints, like paints and bottom paints. arc considered separately in ceeding sections.
The only ite pirpn, m's are white lead and white zinc. the former being a mixture of carbonate and hydrate of lead. and the latter an oxide of zinc. black pignants arc lamp black, boneblack. and graphite. Lampblack is mainly carbon. and result- from the imperfect combustion of oil or gas, the latter being also known as gas black and carbon black. black is the finest in texture of all,pigments, but different lots differ greatly in this respect. The finer grades are tile more valuable. It tains some peculiar oily matter, and retard- the drying of oil more than any other but it is, on the other hand, the most durable. The black pigment most commonly used (except in the special class of paintst is boneblack. known also as drop black. and in the finer grades as ivory black. This contains about 10 or 12 per cent. of free carbon. to NVIIICII it owes its color, the remainder hieing the mineral matter of the bone. 3 or 4 per cent. of bonate. and most of the rest phosphate of lime. Graphite. or mineral crystallized carbon. is tensively used in paint-: it is flaky in structure and in color; like all carbon pigments, it is extremely opaque: it is difficult to grind it to a fine powder. The most brilliant red uiym ts are vermilion and carmine. True vertnilion. or English vermilion. is a sulphide of mercury. It is a pigment of great opacity and beautiful color. and tolerably permanent in ordinary use. Carmine is the most brilliant red known. and is an organic eompound of alumina. such as is technically called a lake. It is rather transparent and is used as a finishing color. Some of the dyes also make red lakes of great permanence and beauty. These reds are the only pigments of importance deriv(d from colors. Various iron oxides form the ordinary and boprn some of these are of a purple shade: all ; re deep in color and have great opacity. TI hydrated oxides are brighter in color dem the anhydrous. .Many of these oxide pigments are made from ores containing clays. whirl wake them brown. or. in the ease of oehres.
Sienna. which. when roasted, i- exactly the color of old mahogany. and is used to stain light woods, is one of these earthy oxides. The most oininion gcllom pigment i- chromate of which .range yellow substance: the paler shades are made by the addition of sulphate of lead at the time of making the chromate. The
pure orange chromate of lead is made by the addition of a solution of liichromate of soda to a solution of nitrate or acetate of lead : by adding sulphate of soda to the bichromate solution. and then mixing this With tilf• lead solution. a mixed preeipitate of chromate and sulphate of lead is produced: the sulphate is. therefore. a proper ingredient in medium and light chrome yellows. By Prussian blue in a shill] tr man Iler with chromate of lead. ehrome greo 11 i- mole. Cadmium is a brilliant and valuable pigment. sulphide of cadmium: the chromate of -trontimttis known as perfect makes a dull and impure kind of yellow. C7 rol,• green is the principal green; it fades badly. Paris green is an arsenical compound of copper, very brilliant, hut not a very opaque pigment. Chronic oxide makes an olive green of a subdued but handsome color. It is probably the only permanent green. Prussian Lim. is a ferrocyanide of iron, dark blue, somewhat resembling indigo; but the most common blue is ultramarine, an artificial substance whose somewhat variable composition is known accurately only to its makers. It is only moderately permanent. The high price of cobalt blue prevents its extensive use; it is more permanent than other blues. The foregoing are the principal opaque body colors. Besides these there is a large class known as Mkes, which are made by precipitating the color ingredients of various dyestuffs with suitable chemicals, usually compounds of alumina, ba rium, or lead. These lakes :ire commonly used to impart a desired tone to the mono opaque pigments. Madder lakes are from madder, and may vary in shade from pink through red and yellow to purple and brown.
See 1.kiiinat.
VI:m(1.Es. Tim principal oil used as a vehicle is linseed. This is made by expression from flaxseed; the (Tilde oil is purified by settling, letting it stand two or three months in tanks at a temperature not lower than 70° F.; it is finally filtered. Linseed oil when spread in a thin film absorbs and combines with oxygen from the air, and is converted into a somewhat elastic leathery substance, commonly known as linoxym A few other oils ha ye this power in a less degree, but only mw equals linseed oil; this is known as tong oil or Chinese wood oil, and appears to excel linseed oil in this respect. It is, however, higher in price than linseed, and darker in color, so that it is not likely to be used.
Damns. Driers act by taking up oxygen from the air and giving it up to the nil. These driers are compounds of lead and manganese, in solution in the oil; these metals ha ye the power of form ing two sets of oxygenated compounds, the peroxidized ones having twice as much oxygen as the others. When in linseed oil they give up half their oxygen to the oil, then, being exposed to the air, they absorb a fresh equivalent of oxygen, which again the oil takes from them: in this way they act as carriers of oxygen from the air to the oil, acting, of course, only when the oil is spread out in a film and exposed to the air. Since the oil is thus converted into a solid dry subsfithee, these agents are called driers.