A covering of gold, when judiciously applied to the proper parts of any object adds greatly to its beauty, and in the case of metals, such as steel, copper, silver, etc., the gold, being capable of resisting the action of most chemical agents, proves a very perfect protector against corrosion. Metals are now generally gilt by means of the electrotype process, though the old method by means of an amalgam, is still used in some cases. Stamped goods, such as cheap jewelry, are also made out of sheets of metal which, after being heavily gilt, are rolled out thin, the gold being thus spread over an astonishing extent of surface. For gliding leather, wood, etc., gold in the form of leaf or powder is generally used.
There are various methods applicable, according to the different circumstances and the character of the objects to be gilded. Book-binders use gold-leaf in two ways - to gild on the edge, and to place gold letters on the binding. To gild on the edge, the edge is smoothly cut, put in a strong press, scraped so as to make it solid, and the well-beaten white of an egg or albumen put on thinly: the gold-leaf is then put on before the albumen is dry; it is pressed down with cotton, and when dry polished with an agate polisher. To put on the lettering, the place where the letters are to appear is coated with albumen, and after it is dry, the type to be used is heated to about the boiling point of water, the gold-leaf put on, either on the book or on the type, and then placed on the spot where the lettering is desired, when the gold-leaf will adhere by the heat of the type, while the excess of gold-leaf loosely around is rubbed off with a tuft of cotton.
To do printing with gold-leaf, the sheet to be printed on is pinned to the tympan of a hand-press, and it is first printed with ink of any color, or with varnish, and then the type is covered with a large sheet of paper, the gold-leaf laid on, and the tympan laid down again, slowly and carefully, so as not to disturb the gold-leaf by motions of the air; then the pressure is again applied, when the gold-leaf will stick to the printed sheet, and the surplus can be rubbed off with a tuft of cotton. Ordinary printing in gold, silver and bronze, however, is done with powdered metal and not with leaf. The printing is first done with a varnish specially made for the purpose; after the impression has been taken, the sheets are allowed to lie a short time so as to dry a little, but not completely, and while still tacky the gold, silver or bronze powder is sprinkled over the letters. The powder adheres to the varnish, and the surplus is easily removed by means of a tuft of cotton.
In gilding picture-frames with gold-leaf there are two methods; one with the ordinary gold size, the other with varnish. The latter method does not allow polishing, but is water-proof; the former is not. The main point is to have a well prepared ground-work of say white lead and drying oil, smoothed down properly; then follow several coats of calcined white lead in linseed oil and turpentine, with intervals of at least twenty-four hours between each coat, which must be carefully smoothed off with pumice-stone and fine emery-paper. Then the gold size is applied, which may be made from the sediment that collects at the bottom of the pot in which painters wash their brushes; this is thoroughly ground and strained. When the gold size coat is sufficiently dry so as to be a little sticky, apply the gold-leaf and press it on with cotton or a soft brush; after a few days' hardening it is varnished with spirits or oil varnish. This gives a water-proof gilding, but ordinarily picture-frames are gilded with a gold size containing no oil. It is made of finely ground sal ammoniac, to which is added a very little beef suet; this is mixed with a pallet-knife, with parchment size dissolved in water, so as to flow from the knife when Lot. The frame may be prepared first with a few coats of Paris white and glue-water, rubbed down smoothly, and finally apply the size, which must not be too thick, as then it will chip off, and if too thin it will not have sufficient body. The most difficult part in all these operations of gold-leaf gilding, is the application of the gold-leaf, which requires much practice, judgment, and great care, but with some attention to little details it can be easily learned. There ought to be no draught at the place of operation and the operator ought to avoid allowing his breath to blow upon the gold leaves, as they are so thin and tight that the least breath of air causes them to fly about - worse than feathers. Turn the gold leaves - one at a time - out of the book upon the leather cushion; with the gilding-knife you may lift any leaf and carry it to a convenient place to cut it into the sizes required. Blow gently on the center of the leaf, and it will at once spread out and lie flat without any wrinkles, then cut it by passing the edge of the knife over it until divided. Place the work to be gilded as near as practicable in a horizontal position, and with a long camels'-hair pencil, dipped in a mixture of water with a little brandy, go over as much surface as the piece of gold is to cover; then take up the gold from the cushion with a tip. Drawing it over the forehead and cheek will dampen it sufficiently to make the gold adhere. This must then be carefully transferred to its place on the work, and by gently breathing on it, it will adhere. Take care that the part to which it is applied be sufficiently wet, so that the gold-leaf will not crack. Proceed in this way, a little at a time, not attempting to cover too much at once. If any cracks or flaws appear, immediately apply another piece of gold-leaf over it - large enough to cover the crack. If occasionally the gold does not appear to adhere, on account of the ground having become too dry, run a wet pencil close to the edge of the gold, so as to allow water to penetrate under the gold-leaf. When the work is dry (say in ten or twelve hours), it may be burnished with an agate tool, taking care to first remove all the dust from the tool as well as from the gilded surface.
Ornamental lines of gilding may be painted on wood and other articles by means of a fine camel-hair brush, using shell gold, which may be had at the artists' supply stores. This forms a very good method of ornamenting work done by the scroll saw, or carved work, such as frames, etc.
Polished steel may be beautifully gilded by means of the ethereal solution of gold. Dissolve pure gold in aqua regia, evaporate gently to dryness, so as to drive off the superfluous acid, re-dissolve in water and add three times its bulk of sulphuric ether. Allow to stand for twenty-four hours in a stoppered bottle and the ethereal solution of gold will float at top. Polished steel dipped in this is at once beautifully gilded, and by tracing patterns on the surface of the metal with any kind of varnish, beautiful devices in plain metal and gilt will be produced. For other metals the electro process is the best.