This method of ornamenting glass is so simple that most people, when they hare it first explained to them, will hardly believe that such simple means can produce such marvellous results. It is done by covering glass with glue, which adheres to the glass, and when the glue dries it shrinks and draws with it pieces of the glass or chip of glass.
The first necessity in carrying out this process is to have the glass which is to be ornamented ground either by means of the sand-blast or by the more troublesome means of grinding by hand. This is done by rubbing a stone with a flat side over the glass till it has lost its polish and become translucent. A thin layer of emery, kept wet with water, will facilitate the grinding, which should be as coarse as possible, and for which reason grinding done by the sand-blast is preferable.
After the glass has been ground it should be kept scrupulously clean. Great care should be exercised that the surface is not touched by the hands. Any trace of grease is very apt to make the results uncertain. If the glass has, however, become contaminated, it may be cleaned with very strong ammonia, although glass which it has been necessary to clean is apt to be rather unreliable.
Good glue is placed in sufficient water to cover it, and allowed to soak for 24 hours. If the water is absorbed during the soaking, more may be added. It is then liquefied over a water-bath, and is then ready to use.
In practice it makes considerable difference which kind of glue is used. By repeated experiments it has been found that Irish glue is the best for the purpose.
A wide brush is dipped in the glue and applied to the glass. The coating should be a thick one, otherwise it will not be strong enough to do the work required. When the plates are coated, they may be placed in racks, and the temperature of the room raised to 95° or 100° F. They are permitted to remain at this temperature till they are perfectly dry, which will be in 10 to 20 hours.
It is at this stage that the uncertain character of glue shows itself. Under certain circumstances the glue will begin to crack and rise of itself without any more manipulations; but most generally it will require to have a stream of cold air suddenly strike it. If the plate is perfectly dry at this period, and of sufficient thickness, the top surface of the glass will be torn off with a noise resembling the crack of a toy pistol. Sometimes the pieces of glue will leap 2 or 3 in. in the air, and may even fly into the eyes and injure them. To guard against this it is customary for the workmen to wear a pair of spectacles fitted with plain glass. The glue will come off sometimes at the least expected times, notably if the plate with dried glue is being carried from one room to another. Plates which have shown a decided disinclination to chip have manifested a remarkable and unexpected activity, and have jumped into the face of the person carrying them in such a manner as to cause him to drop them.
The strength of the glue is something very extraordinary. If the glass has been coated on the hollow or belly side of the glass, the slight leverage thus obtained is almost sure to break it, especially if the glass be single strength. Even plate glass is not unfrequently broken. It might be a rather interestiog mathematical calculation to find out the force necessary to separate the surface of glass in this manner on a piece, say, 48 in. by 48 in.
The result of the operation described may be various. It may be either a design resembling-ferns of various shapes and sizes, or it may be a circular design, exhibiting narrow, feathery appearances; or, if unsuitable glue has been used, it may be of a nondescript appearance.
If, after the glue has been applied, but before it has become any more than set, a piece of stout paper is pressed over it and it is allowed to dry in this way, the glass will have less the appearance of feathers, but will be much coarser, and larger pieces will be removed.
The circular design mentioned occurs under the same circumstances as the other, with the exception that it generally is made during cold weather. Sometimes several weeks may run along and nothing but this formation be made.
Some very elegant designs may be produced by submitting the glass once more to the same operation, covering it as before and allowing the glue to chip. This is known by the name of double chip. If the glass was covered with the small circles in the first place, the second time it will have an appearance very much resembling shells, and for this reason this has been called shell chip.
If, instead of using ordinary glass, coloured glass is employed, pretty and original effects may be obtained. The glass may be either coloured clear through, or it may have only a thin coating on one side. In the latter case, in some places the entire layer of coloured glass will be removed, and in other places only a very little, and will, therefore, give all the gradations between those two extremes.
Glass which has been treated in this way may be silvered and gilded, and thereby be made still more remarkable in appearance.
Extremely elegant effects may be obtained by what is known as "chipping to a line." The design is ground in the glass by the ordinary sand-blast process. After the glass has passed through the machine, the protective coating (wax is generally used) is not removed, but is left on to keep the glue off those parts which are not intended to chip. The glue is then applied in a thick layer to the ground portion, and the process is carried on as usual.
The following, if neatly done, renders the glass obscure yet diaphanous: - Rub up, as for oil colours, a sufficient quantity of sugar of lead with a little boiled linseed oil, and distribute this uniformly over the pane, from the end of a hog-hair tool, by a dabbing, jerking motion, until the appearance of ground glass is obtained. It may be ornamented, when perfectly hard, by delineating the pattern with a strong solution of caustic potash, giving it such time to act as experience dictates, and then expeditiously wiping out the portion it is necessary to remove.
Glass can be drilled with a common drill, but the safest method is to use a brooch drill. No spear-pointed drill can be tempered hard enough not to break. The brooch can either be used as a drill with a bow, or by the hand. It should be selected of such a bore that it will make a hole of the required size, at about one inch from the end. It should be broken off sharp with a pair of pliers, at about 1 1/2 inch, and when the sharp edges are blunted by drilling, a fresh end should be made by breaking off 1/8 inch, and so on, until the hole is bored. It is always desirable to drill from both sides, as it prevents the glass from breaking; drill lightly, and lubricate with spirits of turpentine and oil of lavender, or a little camphor instead of oil of lavender. Holes may be drilled through plate glass with a flat-ended copper drill and coarse emery and water. The end of the drill will gradually wear round, when it mast be re-flattened, or it will not hold the emery. Practically, however, the best means of drilling holes in glass is by using a splinter of a diamond.
A brass drill is made to fit the drill-stock, sawn down a little way with a notched knife to allow the splinter to fit tight, and the splinter fixed in the split wire with hot shellac or sealing-wax. The drill is used quite dry and with care. If the hole to be drilled is wanted larger than the tool, drill a number of small holes close together to form a circle as large as the hole required, then join the holes with a small file.- A splinter of diamond may be bought for 2s. big enough to drill a 1/4 in. hole. (See also iii. 231, v. 315.)
Roll up tolerably tightly a slip of tin, about 6 in. or 8 in. long and about 2 in. broad, or use a small flat piece of marble. Dip either of these in Croydon or glass-cutters' sand, moistened with water; rub over the glass, whether flat or round, dipping it frequently in a pail or pan of clear water. This is the method employed for frosting jugs, etc. For lamp glasses a wire brush is used, and they are chucked in a lathe. Panes of glass should be laid on a soft bed of baize, or coarse linen. If the frosting is to be very fine, finish with washed emery and water. As a temporary frosting for windows, mix together a strong, hot solution of sulphate of magnesia and a clear solution of gum arabic, apply warm. Or use a strong solution of sulphate of sodium warm, and when cool wash with gum-water to protect the surface from being scratched. (See also iii. 23+, v. 319.)
Stencil plates may be cut out of thin sheets of metal or cardboard, in the same manner as for wall decoration, etc. If varnish colours are employed, lay them on as evenly as possible, through the perforations in the plate, and harden afterwards in a stove or oven. The metallic preparations used in glass staining and painting are also available, but require firing in a muffle, or a china-painters* stove. Should the process commonly called embossing be wanted, paint the portions of glass left uncovered by the spaces in the stencil plate with Brunswick black, dip or cover with hydrofluoric acid, wash in clear water and remove the black ground. Every part that was covered will then present a polished even surface, the remainder will have been eaten into by the acid. If the raised parts are to have a frosted appearance, rub them with a flat piece of marble moistened with fine emery and water. For putting patterns or lines on glass with a wheel, there are two methods, one followed by glass cutters, the other by the engravers on glass.
According to the first-mentioned, rough in the pattern with an iron mill supplied with a trickling stream of sand and water, smooth out the rough marks on a wheel of York or Warrington stone, polish on a wooden wheel of willow or alder powdered with pumice, and finish on a cork wheel with putty and rotten-stone. The engraver cuts in and roughs the pattern with copper wheels, aided by emery of various degrees of fineness, and olive or sperm oil, and polishes the portions intended with leaden disks and very fine pumice powder and water.
Metallic colours, prepared and mixed with fat oil, are applied to the stamp on the engraved brass or copper. Wipe with the hand in the manner of the printers of coloured plates; take a proof on a sheet of silver paper, which is immediately transferred on the tablet of the glass destined to be painted, being careful to turn the coloured side against the glass; it adheres to it, and so soon as the copy is quite dry, take off the superfluous paper, by washing it with a sponge; there will remain only the colour transferred to the glass, which will be fixed by passing the glass through the ovens.