A special form of gold leaf is known as rib bon gold. This is thicker than the ordinary leaf and consequently more expensive. It is put up in long ribbons or strips of uniform width, rolled with a continuous strip of paper in a similar manner to rolls of silk ribbon. This gold is used for striping, and is applied by means of a small machine that is known as the gilding wheel.
Silver leaf tarnishes very readily, being af fected by the sulphur gases in rooms lit by ordi nary illuminating gas or heated by coal fires, and is therefore very little used. Its place is now usually supplied by aluminum leaf, which does not discolor under ordinary conditions, although its luster is slightly inferior and its color grayer.
Copper leaf turns a deep rich red or brown unless protected by lacquer or varnish.
Operation of Gilding. One of the greatest difficulties connected with the application of gold leaf is its tendency to stick to any moist sur face. The workman dare not even touch the gold leaf with his hands when loose gold leaf is used, or the sheet will adhere to them and be ruined. The knives and other tools used in gilding must be kept very clean and perfectly dry, for the same reason.
The first thing necessary to do in gilding is to coat the exact surface to which the leaf is to be applied, taking care to keep the outlines sharp, with a size of some kind depending on the nature of surface. The most usual size is
known as oil gold size or fat oil. This is made by allowing linseed oil to stand in an open jar until it becomes partially oxidized, from time to time carefully skimming off the thick skin which forms on its surface. It takes from six to twelve months before the oil is ready to use. Another oil size is made by boiling the oil. A quick-dry ing oil varnish known as gold size japan is also used. The advantage of this size is that it is ready for gilding in from ten minutes to a half hour after application, but it is by no means as durable and loses its elasticity. For this reason the oil gold size should always be used for out side work on wood or metal. In gilding upon these materials the surface should ordinarily be prepared by giving it several coats of paint, the last one being flat and sandpapered perfectly smooth. A trifle of chrome yellow is usually mixed with the gold size in order that it may show more distinctly and enable the painter to see that the surface is thoroughly covered and that the outlines are sharp. Gilding can also be done upon varnish, the main thing being to have a smooth surface as nearly non-absorbent as pos sible, to which the gold size will adhere.
Gilding on glass, such as the signs on sho \\ windows, requires a special treatment. The gold leaf is applied on the inner side of the window, showing through the glass, and for this reason a perfectly clear size must be used. That which is usually employed is a very weak solution of the finest Russian isinglass in boiling water. Special sizes are also made for gilding picture frames and for other purposes.
For gilding lines or stripes the ribbon gold is preferable to the leaf. The stripe is first care fully drawn with a special form of brush known as the striping pencil. This requires a very ex pert workman. A small striping wheel may be used, which mechanically feeds the color or gold size to a rubber and cloth disk, the width of which can be varied at will. By using this striping wheel and ribbon gold on the gilding A wheel, mechanically perfect gilded stripes can be produced in one-tenth the time (or even less) that would be required by ordinary methods.