GILDING, the art of spreading gold, either by mechanical or chemical means, over the surface of a body for the purposes of protection or ornament. The art of gilding was known to the ancients. According to Herodotus, the Egyptians were accus tomed to gild wood and metals ; and gilding by means of gold plates is frequently mentioned in the Old Testament. Pliny in forms us that the first gilding seen at Rome was after the de struction of Carthage, under the censorship of Lucius Mummius, when the Romans began to gild the ceilings of their temples and palaces, the capitol being the first place on which this enrich ment was bestowed. Owing to the comparative thickness of the gold-leaf used in ancient gilding, the traces of it which yet remain are remarkably brilliant and solid. Gilding has in all times oc cupied an important place in the ornamental arts of Oriental countries ; and the native processes pursued in India at the present day may be taken as typical of the arts as practised from the earliest periods.
Modern gilding is applied to numerous surfaces and by various processes, making the art an important part of widely different ornamental and useful arts. It forms an important and essential part of picture framemaking (see FRAME), is largely employed in connection with cabinet-work, decorative painting and house ornamentation, and is of great importance in bookbinding and ornamental leather work. Further, gilding is much employed in electro-gilt reproductions and in electro-plating, and is also a characteristic feature in the decoration of pottery, porcelain and glass. Any of these various processes may, however, fall under one of two heads—mechanical gilding and chemical gilding.
This embraces all the operations by which gold-leaf is pre pared (see GOLDBEATING), and the several processes by which it is mechanically attached to the surfaces it is intended to cover. It thus embraces the burnish or water-gilding and the oil-gilding of the carver and gilder, and the gilding operations of the house decorator, the sign-painter, the bookbinder, the paper-stainer and several others. Polished iron, steel and other metals are gilded mechanically by applying gold-leaf to the metallic surface at a temperature just under red-heat, pressing the leaf on with a burnisher and reheating, when additional leaf may be laid on. The process is completed by cold burnishing. Copper and wood are perhaps the most widely used bodies for the appli cation of gilding.
Copper Gilding.—For the gilding of copper, employed in the decoration of temple domes and other large works, the follow ing is an outline of the process employed : The metal surface is thoroughly scraped, cleaned and polished, and then sufficiently heated in a fire to remove any traces of grease or other impurity which may remain from the operation of polishing. It is then dipped in an acid solution prepared from dried unripe apricots, and rubbed with pumice or brick powder. Next, the surface is rubbed over with mercury, which forms a superficial amalgam with the copper, after which it is left some hours in clean water, again washed with the acid solution and dried. It is now ready for receiving the gold, which is laid on in leaf, and, on adhering, assumes a grey appearance from combining with the mercury, but on the application of heat, the latter metal volatilizes, leav ing the gold a dull, greyish hue. The colour is brought up by means of rubbing with agate burnishers. The weight of mercury used in this process is double that of the gold laid on, and the thickness of the gilding is regulated by the circumstances or necessities of the case. For the gilding of iron or steel, the sur face is first scratched over with chequered lines, then washed in a hot solution of green apricots, dried and heated just short of red-heat. The gold-leaf is then laid on, and rubbed in with agate burnishers, when it adheres by catching into the prepared scratched surface.
Wood Gilding.—In applying gilding to wood, after the sur face has been sand-papered in order to remove all sharp edges, followed by a very careful dusting, the glue priming size stage is of first importance.
Priming.—Glue size is made by mixing an ounce of glue to a gill and one-half of water, and allowing it to soak at least two hours, after which the mixture is placed in a double boiler and heated until it has become all liquid ; then it is removed to set. The combination, which is of jelly-like appearance, can then be cut into blocks or squares, and is generally known as the stock glue size. It is the supply base for all following sizes where glue is used as an ingredient.
Sizing, a term used mostly by painters, is primarily applied to the act of glazing the surface of the material to be gilded. For this preparation, the stock glue size is thinned by mixing a two thirds proportion of water and dissolving the combination by heat in a double boiler, being careful not to place the vessel near an open fire.
It is necessary for this size to be painted on the raw wood when the combination is still warm. It is well also to have the surface moderately warm so that the size will not form a film on the surface of the wood, but will soak into the grain and act as a filler. It is also necessary to remove any superfluous liquid and blank spaces that may appear just after the glue size is applied. From two to five hours are required for the wood to dry. The glue priming size is followed by the whiting size. This size is made by adding another one-third portion of water to the stock glue size and then heating.
The First Coat of IV hiting.—After this mixture has reached the proper temperature, which is somewhat under boiling, sprinkle in the best quality of bolted whiting until the mixture becomes a thick cream.
The first coat of whiting should be applied in a stipple-like fashion, which enables the second coat to have a gripping sur face on which to take a better hold. This stippling should be given at least two hours to dry. After the first coat has been applied and allowed sufficient time to dry, the surface should be carefully examined for imperfections such as miscuts, openings at joints, or nail holes. These imperfections require considerable care in filling with putty, made in the following manner : Putty Filler.—Make a depression in the stock dry whiting, and pour in a small amount of stock size glue, which should be heated. Take a putty stick and work it around until it becomes a doughy mass of whiting and glue. When it has finally been kneaded sufficiently to allow handling, work it in the palm of the hand until it becomes as pliable as common painter's putty. In placing this prepared putty into the blemishes on the wood, moisten each particle immediately before putting it into place. It is also advisable to use a little moisture in smoothing over the surface and removing any superfluous putty.
The second coat of whiting or filling coat is also called the smooth coat. It is applied as evenly and smoothly as possible, with the exception of the parts that are desired to retain a stippled effect, in which case, the stipple is repeated and applied on the parts as in the previous coat. Do the stippling before finally smoothing the other surfaces with a brush.
The third coat, if necessary, is next applied. This all depends on the surface to be gilded and the amount of ornamentation, and is mainly intended to produce a pleasing effect. When the desired body of whiting has been applied and has dried for at least two hours, the parts which are to remain smooth are rubbed down with a damp cloth. If necessary, especially in deep orna mentation, a brush will answer this purpose better. After the moist smoothing of the surface has been accomplished, it is gone over with a fine piece of sandpaper (o or oo) in order to remove the burr which is caused by the damp smoothing. After removing all dust after sand-papering, it is ready for its first coat of gold size.
Gold Size is applied in much the same manner as paint would be applied, which means working it out smoothly so as to prevent any surplus remaining in corners or causing puddles. Where ornamentation is deep, puddles or floods in hollows are causes of crackling and endless trouble, and one of the most common warnings to an apprentice is, "Don't let the depths fill up." A Second Coat, and sometimes a third, is applied in like man ner, being careful again to allow the surface to dry well after each application and sandpaper to remove any surface burrs. After this, the wood is again dusted off carefully and a coat of very weak size is applied, by heating a piece of stock glue until it is completely dissolved. This weak size must not be applied in a hot state and must be of an even, cool temperature before applying; in fact, less warm than lukewarm. The weak size must be applied by a long soft-haired brush, avoiding puddles in the depths and with such a gentle touch that you do not disturb the gold size. A weak size solution is made as follows : A piece of stock size glue the size of a lima bean dissolved in one gill of hot water, allowed to cool, add a few drops of denatured alcohol.
Burnished gold size is made as follows: Take a desired amount of the basic (red clay, blue clay or any one of many more colours as it comes in the jar) place it in the vessel and add cold water. Stir until it has reached such a consistency that the brush will stand upright in it, then place it in the heater to remain only long enough to take off the chill. The stock glue, having previously been placed in a heater to bring to a very high temperature, is poured, a little at a time, into the clay, stirring the mixture in a rapid, agitative manner, adding glue until it reaches the con sistency of just wanting to drip from the brush in a heavy, creamy form; the jar containing the burnished gold size is covered and allowed to set over night to ascertain its strength, which should be of a jelly consistency.
A test of gold size for immediate use is made as follows : Apply very thinly, a coat of the size on the thumb nail or two other finger nails, so that it may dry through the heat of the finger and fanning in the air. When this has dried, take the opposite thumb nail and begin to burnish the nail that holds the gold size. If it comes off, it lacks glue; if it is dull and slaty looking, it lacks body clay; but if it burnishes by the finger nail action and has a mellow lustre, the test is successful and the size is ready for use.
Hints on Application.—Gold size must never be cold, nor can it be warm when it is applied. In laying gold-leaf with the hair tip, a solution of a few drops of alcohol in water should be added to the gold sizing before the leaf is flipped on. Also, if possible, keep the wood tilted so that the liquid will run down and not remain in puddles in any one spot. Burnishing must be done within 48 hours, the sooner the better, after the liquid and gold size have dried; but the minimum should be four hours for drying. After burnishing the surface, it may be necessary to apply small patches of gold in spots where it did not adhere in the first laying.
Faulting, or patching, is done in the same manner as gilding with the exception that the solution in this case should contain a greater percentage of alcohol, which quickens the drying. Small patches dry in about 3o minutes. After the patching has been completed, then, with a soft brush, preferably goat hair or badger, dust off all surplus particles of gold, so that they will not mix with the lacquer which follows. When the burnishing has been done, take some weak size and with a camel's hair brush, apply very lightly a coat all over, not with a heavy brush motion, but just laying it on. When dry, which takes about one hour, the wood is ready for lacquering.
Lacquering is the process in which pure white shellac, diluted with denatured alcohol until it flows in a watery state, is applied with a camel's hair brush in a light manner. The lacquer must dry for about ten hours, after which the wood is ready for toning.
Any desired effect may be obtained by dissolving a pigment with turpentine and adding a few drops of painters' dryer, which acts as a binder. It should have the consistency of thin, trans parent white raw umber or zinc white. This medium is freely applied, allowing it to settle into the depths, removing the sur plus from all high light with cheese cloth or soft, absorbent cloth. After a few moments, the final effect can be obtained by an additional light wiping with the cloth, although the best re sults are often obtained by using the fingers instead of a rag. It is advisable not to tone, at any one time, a greater surface than can be kept under control, because within ten minutes, this tone so strongly adheres to the lacquer that erasure is difficult.
(A. E.)