(a) Drinking and other glasses are sometimes gilt on their edges. This is done either by an adhesive varnish or by heat. The varnish is prepared by dissolving in boiled linseed oil an equal weight either of copal or amber. This is diluted by a proper quantity of oil of turpentine, so as to be applied as thin as possible to the parts of the glass intended to be gilt. When this is done, which will be in about 24 hours, the glass is to be placed in a stove, till it is so warm as almost to burn the fingers when handled. At this temperature the varnish will become adhesive, and a piece of leaf gold, applied in the usual way, will immediately stick. Sweep off the superfluous portions of the leaf, and when quite cold it may be burnished, taking care to interpose a piece of very thin India paper between the gold and the burnisher. If the varnish is very good, this is the best method of gilding glass, as the gold is thus fixed on more evenly than in any other way. (b) It often happens when the varnish Is but indifferent, that by repeated washing the gold wears off; on this account the practice of burning it in is sometimes had recourse to.
For this purpose, some gold powder is ground with borax, and in this state applied to the clean surface of the glass by a camel-hair pencil; when quite dry, the glass is put into a stove heated to about the temperature of an annealing oven: the gum burns off, and the borax, by vitrifying, cements the gold with great firmness to the glass; after which it may be burnished. The gilding upon porcelain is in like manner fixed by heat and the use of borax.
(c) The glass must be thoroughly cleaned and polished. A size must be prepared as follows: - Isinglass 1 oz., dissolve in just sufficient water to cover it; when dissolved, add 1 pint rectified spirit of wine, then increase the quantity to 1 qt. with water; keep-tightly corked. Or, take best rum 1/2 pint, isinglass, 1/4 oz. Dissolve the isinglass in the rum at a low temperature, then add 1/2 pint distilled water and filter through a piece of old linen. Place the glass fiat on a perfectly level table, then with a clean brush flood the glass with the size to the depth of 1/8 in., raise the gold leaf with a tip and lay it flat on the size; it will almost instantly adhere to the glass; in 5 minutes afterwards place the glass endways at a slight angle against a wall, that the surplus size may drain off. Allow the glass to remain in that position for 24 hours, by that time it will be perfectly dry. Draw the pattern or letter on a piece of paper, and with a thick needle pierce holes on the lines at the distance of 1/16. in. apart; place the pounced paper on the gold surface, then dust some powdered whiting well on the paper that it may penetrate the holes; remove the paper carefully, and there will remain a correct copy of the design on the gold.
Now fill up the outlines of the design with oil gold-size in which has been ground some orange chrome, thin it with a little boiled oil and turpentine. When thoroughly dry, wash off the surplus gold with water and a piece of cotton-wool. Back the glass with any suitable colour.
The gold used is the ordinary gold leaf. Procure some fine isinglass, and place about as much in a tea-cup as will coyer a sixpenny piece, and then pour on it about half a cupful of boiling water, which will dissolve the isinglass. Before the water is cold add about as much spirits of wine as there is water in the cup; then strain the whole through a clean silk handkerchief, and the mordant is ready for use. The addition of the spirits of wine is most material, as without it the gilding cannot be satisfactorily accomplished. Whatever may be the design or lettering, it must first be set out on a sheet of white paper, and painted with Brunswick black, so that it can be seen on the reverse side. This paper with the writing reversed should be fixed at the edges or corners to the glass, the writing, of course, appearing backwards. The glass having been thoroughly cleansed and rubbed with a silk handkerchief, the gilding may be commenced, the gold leaf being laid on the reverse side to that to which the paper is attached. It is usual to place the glass in a slanting position on an easel, the lines of lettering not being horizontal, or reading from left to right, but perpendicular, reading from top to bottom.
The mordant is put on with a large soft camel-hair pencil, and the gold leaf is lifted from the cushion and placed on the mordant with a tip, after having been cut to the required dimensions. If the line of writing is less than 3 in. high, it is advisable to gild the whole line, without paying any regard to the shapes of the letters, so that when the line is finished it will be a solid piece of gilding about the same height and length as the letters. The first piece of gold leaf should be placed at the beginning of the line, which is the top of the glass, and each succeeding piece below it, the different pieces just overlapping each other. It is necessary to be particular in this, for if the pieces of gold do not meet, the interstices will probably show when the work is completed, and will prevent the uniformity of burnish. For letters larger than 3 in. high, the gilding may be made to cover each letter, leaving the spaces between untouched.
As soon as this part of the gilding has been completed, it should be left to dry in a warm room, or placed before the fire, in which case it will be dry in a few minutes. When the gilding is perfectly dry and bright, it should be rubbed over very gently with a piece of cotton-wool. This will heighten the burnish of the gold, and remove the loose pieces which do not adhere to the glass. After the gilding has been treated as described, a flat soft camel-hair brush charged with the isinglass size should be passed lightly over the work; but not worked too and fro, or it will remove the gold leaf. The size should he flowed on freely and rapidly, and if any small pieces have been omitted, no attempt should be made to retouch them while the size is wet. When it is dry, the gilding will resume its brightness. In order to complete the burnish of the gold, sometimes hot water is poured over the gilding, and this not only washes out any little specks which may appear on the front of the gold, but enhances its brilliancy considerably. The hotter the water poured over the work, the brighter does the gilding become, but care must be taken, as beyond certain degrees of heat the water will break the glass.
The hot-water bath now is often dispensed with, and the size coated over the gilding is applied hot. This method is not quite so effective but it is much safer. The whole of the gilding has now to be repeated. A second layer of gold leaf over the first is necessary to ensure a satisfactory result. The second coat of gold is put on with the isinglass size, the same as the first; and as it dries, the gilding viewed from the front of the glass will present a rich and finished appearance. The loose pieces of gold should be removed as after the first coat, by means of cotton-wool gently rubbed over the work. Another coat of size made hot may now be applied, and the gilding is ready to be written upon. It is better to leave the gilding on for a day or two before writing upon it, because the isinglass does not get thoroughly hard, though to all appearance it is perfectly dry in an hour or two. If the gilding is left untouched for 2-3 months, the action of the spirits of wine will cause the gold leaf to adhere so firmly to the glass that it will be difficult to remove it by any amount of washing with-water; whereas in the course of a few days after it is laid on, it may be readily removed by a damp sponge. There are several ways of transferring the outline of the writing to the gold.
The most expeditious method is to rub some dry whiting over the front side of the writing, on the paper, place this over the gilding, face downwards, then go over the outline of the letters with a pointed stick or hard pencil. On removing the paper, it will be found that where the letters have been traced, the whiting has marked the gold. Having an outline of the writing or design, next paint the letters with a sable writing pencil, and the ordinary japan black used by coach painters. If on turning the glass round it should be seen that the japan black deadens the gilding or is perceptible in any way on the front of the glass, another coat of size should be passed over the gold to prevent the black from coming through the gold leaf. When the japan black is hard, the superfluous gold must be washed off with a sponge and warm water. When the japan is dry, the edges of the letters may be cut sharp and true by passing a small chisel along a straight edge, so as to trim the writing, and make the tops and bottoms perfectly regular. All the straight lines of the letters may be thus trimmed, but the curved ones must be perfected with a writing pencil.
The softened coloured thicknesses added to the letters are painted with the ordinary oil colours thinned with boiled oil and turpentiue, the Jatter being used sparingly. Three or more tints are generally mixed on the palette, with a separate pencil to each, and these are softened with a larger sable pencil, and the outer edges are cut up with a pointed stick guided by a straight edge, whilst the colour is wet, and the superfluous colour is wiped off with a piece of rag. By this means a shanmess of outline is obtained which the most skilful writer would fail to get by the mere use of the pencil. The shadow is put on as soon as the thickness is dry, and not being softened down, quick drying colours may be em-ployed.