Painterwork accomplishes two things, namely the preservation and the coloration of the material which is painted. The compounds used for painting, taking the word as meaning a thin protective and/or decorative coat, are very numerous, including oil paint of many kinds, distemper, whitewash, tar; but the word paint is usually confined to a mixture of oil and pigment, ground together in a process that thoroughly coats every small particle of pigment in oil, together with other materials which possess properties necessary to enable the paint to dry hard and with a degree of flexibility and to varying degrees of opacity/translucency. Oil paints are made up of four parts, the base, the vehicle, the solvent and the driers. Pigment may be added to these to obtain a paint of any desired color. There are several bases for oil paint, those most commonly used for building work being white lead, red lead, zinc white and iron oxide.
White lead is a base for paint. It is poisonous, and must be used with care, if used at all. When pure it consists of about 75% lead carbonate and about 25% of lead hydrate. It is mixed with 6 or 7% by weight of pure linseed oil, and in this form is supplied to the painter. Sulfate of baryta is the chief adulterant used in the manufacture of white lead. White lead has greater covering properties and is more durable than the other bases. It should therefore always be used in external painting. Paints having white lead for a base darken with age, and become discolored when exposed to the fumes of sulfuretted hydrogen, which exists to a greater or less extent in the air of all large towns. Zinc white, an oxide of zinc, is of a purer white color than white lead. It is lighter, and does not possess the same durability or covering power. It is, however, useful in internal decoration, as it retains its color well, even when subjected to the action of gases. Red lead is a lead oxide. It is used chiefly in the priming coat and as a base for some red paints.
Like white lead, it is injured if exposed to acids or impure air, which cause discoloration and decay. Oxide of iron is used chiefly as a base in paints used for covering ironwork, the theory being that no destructive galvanic action can be set up, as might be the case with lead paint when used on iron. A variety of red pigments are made from oxide of iron, varying in hue from a pale to a deep brownish-red. They are quite permanent, and may be used under any conditions. The vehicle is a liquid in which the particles of the base are held in suspension, enabling a thin coat of paint to be formed, uniform in color and consistency, and which on drying forms a kind of skin over the surface to which it is applied. For oil paint the vehicles used are oils; for distemper water is employed. The oils used as vehicles are chiefly linseed oil, raw and boiled, and poppy-seed oil. Nut oils are occasionally used for inferior work because they are much cheaper. Linseed oil, the one most commonly used, is obtained from the seeds of the flax by warming it and squeezing out the oil under hydraulic pressure. The resultant, which is of a transparent amber color, is known as raw oil. It is used principally in interiors for light, bright colors, drying somewhat slowly and giving a firm elastic coat. The oil improves by keeping, and is sometimes refined with acids or alkalis.
Boiled oil is the raw oil heated with driers, such as litharge or red lead, to a temperature from 350° to 500°F, at which it is maintained for three or four hours. It is thick and much darker in color than the raw oil, drying much more quickly, with a coat hard and glossy but less elastic than that produced by raw oil. Poppy-seed oil is expressed from the seeds of the poppy plant. It does not possess the tenacity and quick-drying powers of boiled linseed oil, but being of a very light color it is used for delicate colors. Turpentine is used as a solvent, diluent, or thinner, to bring the paint to a proper consistency so as to allow it to be spread in a thin even coat. When a flat dull surface is desired, turpentine alone is used with the base and the oil is omitted. The best turpentine comes from the pine forests of America. French turpentine is next in quality. Russian turpentine is the cheapest, and has usually a strong and unpleasant odor that renders it objectionable to work with. In consequence of the high price of turpentine of good quality, and the increasing difficulty of obtaining it, substitutes are coming into general use. Driers are substances usually added to paint to hasten the process of oxidation, i.e. the drying, of the oil. Some pigments possess this quality, as red lead and white lead.
The most notable driers are litharge, sugar of lead, patent driers, sulfate of zinc and manganese dioxide. Liquid driers, such as terebene, are also in use. Litharge, an oxide of lead, is in most general use. Sugar of lead is used, ground in oil, for light tints. Sulfate of zinc and manganese driers are used for paints in which zinc white is the base, which would be injured by lead driers. Pigments are preparations of metallic, earthy or animal origin mixed into paint to give it color. For oil paint they are usually ground in oil; for distemper they are sold as a finely ground powder. The ordinary pigments are white lead, zinc white, umbers, siennas, ochres, chromes, Venetian red, Indian red, lampblack, bone black, vegetable black, ultramarine, Prussian blue, vermilion, red lead, oxide of iron, lakes and Vandyke brown. The term enamel paint was first given to a compound of zinc white, petrol and resin, which possessed on drying a hard glossy surface. The name is now applied to any colored paint of this nature. Quick-drying enamels are spirit varnishes ground with the desired pigment. For slow-drying enamels oil varnishes form the vehicle.
Woodwork is often treated with a thin transparent-colored liquid that changes the color of the work without hiding the grain of the wood, and if the latter is good a very fine result is obtained. Sometimes the stain is produced by the combination of two or more chemicals applied separately, or soluble pigments may be mixed with a transparent vehicle and applied in the usual way. The vehicles for the pigments vary considerably, and include water, methylated spirit, size, turpentine and clear raw linseed oil. Varnish is made by dissolving certain gums in linseed oil, turpentine, spirit or water. They give a transparent protective coat to painted and stained surfaces or to wallpaper or plain woodwork. Varnishes usually dry with a very smooth, hard and shiny surface, but flat or dead surfaces that are without gloss may be obtained with special varnish. The gums used for hardwearing or carriage varnishes, such as those to be exposed to the weather and frequently cleaned and polished, are amber, copal and gum anime. Amber is a yellow transparent or clouded gum found on the coasts of the Baltic, and particularly in Prussia. It makes a hard, durable and slow-drying varnish that does not darken with age. Copal gum is brought from the West India Islands and also from the East Indies. It makes the most durable varnish, and being tough and hard is generally used for external work. Gum anime, is a variety of copal found in the sandy soil of the East Indies.
It is hard, durable and quick drying, but unless the varnish is carefully made it is liable to crack. Varnishes for inside work, or cabinet varnishes, are made with a variety of resins dissolved in linseed oil and turpentine. The resultant gives a hard, lustrous surface, somewhat less durable than that of carriage varnishes. Turpentine varnishes are made from soft gums, such as dammar, common resin and mastic; they are light in color, cheap and not very durable. Lacquers or spirit varnishes are made from very soft gums, such as shellac and sandarach, dissolved in methylated spirit. They are used for internal work, drying quickly, and becoming hard and very brilliant. Surfaces formed with such varnishes are liable to chip easily and scale off. Oil paint is very much improved by the addition of some varnish; it causes it to dry harder and more quickly and with a fine lustrous surface. The driers used for varnish are generally acetate of lead or litharge. An excess of driers makes the varnish less durable and causes cracking. There are many kinds of French polishes, mixed in different ways, but most are composed of shellac and sandarach dissolved in spirit. It is applied to the perfectly smooth surface of hard woods with a pad of flannel or wadding wrapped in linen, and well rubbed in with a circular motion.
A dull polish is procured by rubbing beeswax into the wood. It must be thoroughly rubbed in, a little turpentine being added as a lubricant when the rubber works stiffly. If paint were applied over the bare knots of new wood it would be destroyed, or at least discolored, by the exudation of resin from the knots. For the purpose of obviating this the knots are covered with two coats of a preparation called knotting, made by dissolving shellac in methylated spirit. Putty is required for stopping nail-holes and small crevices and irregularities in woodwork. It is made of powdered whiting and linseed oil mixed together and kneaded into a stiff paste. For light work hard stopping, made of white lead and whiting, should be employed. The tools and appliances of the painter are mixing pots, paint kettles to hold the color for the painter at work, strainer, palette knife, scraping knife, hacking, stopping and chisel knives, the hammer, sponge, pumice, blow-lamp for burning off, and a variety of brushes, such as the duster, the ground brush, the tool, the distemper brush, the fitch and camel-hair pencil for picking out small parts and lines, the sable and flogger for gilding, the stippler; for grained work several steel graining combs with coarse and fine teeth, graining brush of hogs' hair, pencil over-grainer, and other special shaped brushes used to obtain the peculiar characteristics of different woods. It is absolutely necessary for good work to use brushes of a fine quality, and although expensive at first cost, they are undoubtedly cheapest in wear.
New woodwork requires to be knotted, primed, stopped, and in addition painted with three or four coats of oil color. The priming coat is a thin coat of white lead, red lead and driers mixed with linseed oil and turpentine. Work should always be primed before the stopping is done.
The second or lead coat is composed mainly of turpentine, linseed oil and white lead. The third coat is the ground for the finishing color, and is made of white lead and linseed oil and turpentine, with enough pigment to bring it to a tint approaching the finishing color. The remaining coat or coats is of similar composition. A flatting coat is made of white lead and turpentine with the desired pigment. One pound of color will cover 4 square yards in the first coat and 6 square yards in the additional coat.
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