Bronzing Gold. Size is japanners' gold size kept till very bright and tough from age, and then heated up and mixed with 1 gal. very old carriage varnish to 9 gal. gold size. This is used for laying on bronze and also gold, by writers, grainers, japanners, and gilders. The greater the proportion of carriage varnish, the slower it will dry. Some paper-stainers like it to dry quicker than others, and writers and grainers like it to dry quicker than gilders and japanners.
Fat-oil Gold-Size is made by grinding good Oxford ochre very fine in old fat linseed oil; when ground as stiff as possible, it ought to be kept for several years before it is used*; the longer it is kept the better it becomes, as it acquires a rich mellow fatness. When this size is to be applied to work, take as much as is necessary, and mix it up with a little good fat boiled oil to a proper consistence, neither too stiff nor too fluid; then apply the size to the ground, laying it very regularly and rather fully, yet not so as to run or fall into wrinkles. Gilding with oil size is suitable for large picture or looking* glass frames, figured or lettered signboards, clock faces, and various articles exposed to the weather, where a great breadth of gilt surface is required, as it possesses more durability and boldness than any other kind of gilding, particularly when the gilding is varnished before it becomes foul. When it is necessary to re varnish old gilding in oil, such work ought always to be well oleaned from dust, grease, or any incrustation which covers the surface, otherwise the varnish will not dry off hard, but will remain cloudy and tacky, so as readily to retain dust and flies.
Various methods are employed by painters and gilders to clean old gilt work. Some wash the work well with a crush or sponge, which is sufficient in cases where the ground is firm, hard, and of a metallic colour; but where the grounds are absorbent, with gold letters, simply washing with water is in general insufficient. In such cases, employ an alkaline lye, made by dissolving 2 oz. pearlash in 3 pints water; then wet the work over with a brush or sponge dipped in the lye; let it remain some time, afterwards, with the sponge and clean water, wash off a part to see if the surface or gilding is properly clean, when it must be thoroughly washed with plenty of pure water, and wiped dry with a soft cloth or silk handkerchief. Oil of vitriol and water mixed until its acidity is equal to that of vinegar, is very cleansing, but requires considerable practice to apply it equally to the work, and it must not remain on too long, otherwise it will not only remove the dirt, but also the paint and gilding; it requires to be used with caution, frequently applying the sponge and clear water, in order to discover whether the surface is clean. When it is well washed and wiped dry, let the work stand to dry, and afterwards apply one or two coats of copal varnish.
In revarnishing old work exposed to the weather, it is best to clean it over-night, and if the weather is fine next morning, and no appearance of rain, high wind, or dust, apply the varnish about sunrise, when the warmth of the sun will cause it to flow, set, and dry quickly and hard.
Put 12 gal. linseed oil into the iron set-pot; as soon as it has boiled 2 hours, gradually introduce 12 lb. litharge. Continue the boiling very moderately for 6 hours; let it remain until next morning, then bring it to simmer, and run 10 lb. gum animi and 2 gal. oil. When these two runs of gum are poured into the iron pot, put in 7 lb. Burgundy pitch; continue the boiling, and keep ladling it down, as directed for the best gold size, boil it moderately strong, but not over-strong, and when right, mix it with 30 gal. turpentine, or more if required; this should be left a little thicker and stronger than japanners' gold size, as it is used for paper-stainers to lay their flock on, and ought to dry slowly in 1 hour.
Gold powder may be prepared in three ways, (a) Put into an earthen mortar some gold leaf, with a little honey, or thick gum-water, and grind the mixture till the gold leaf is reduced to extremely minute particles. When this is done, a little'warm water will wash out the honey or gum, leaving the gold behind in a powdered state.
(6) Dissolve the pure gold, or the leaf, in nitro-muriatic acid, and then precipitate it by a piece of copper, or by a solution of iron sulphate. The precipitate, if by copper, must be digested in distilled vinegar, and then washed, by pouring water over it repeatedly, and dried. This precipitate will be in the form of very fine powder; it works better and is more easily burnished than gold leaf ground with honey as above.
(c) The best method of preparing gold powder is by heating a prepared amalgam of gold, in an open clean crucible, and continuing the strong heat, until the whole of the mercury is evaporated; at the same time constantly stirring the amalgam with a glass rod. When the mercury has completely left the gold, the remaining powder is ground in a Wedgwood mortar with a little water, and afterwards dried. It is then fit for use. Although the last mode of operating has been here given, the operator cannot be too much reminded of the danger attending the sublimation of mercury. In the small way here described, it is impossible to operate without danger; it is therefore better to prepare it according to the former directions than to risk the health by the latter.