Water gilding is a simple immersion process, and may be effected by dissolving 5 oz. of gold converted into chloride with 4 gal. of water, and boiling it with 20 lb. of pearlash for several hours, the articles to be immersed for a few minutes in the solution, which is kept warm.
Gilding by means of a separate current is best conducted with the solution of the double salt of cyanide of gold and potassium. When formed chemically, this salt is prepared by adding cyanide of gold to a solution of cyanide of potassium, and evaporating to dryness ; the resulting crystals con stitute the double salt, and form an excellent plating solution alone, when dissolved in water. Other solutions, such as that composed of yellow prussiate of potash, 7 oz.; pearlash, 5 oz. ; sal ammoniac, 1 oz. ; pure gold transformed into chloride, 2 oz.; and water, 2 gal.; the salts are boiled togethtr, and the chloride of gold added, dissolved in a little water just before the bath is allowed to cool. The anodes employed are plates of thin gold dipped entirely into the bath, and held by small platinum wires connected to the positive pole of the battery. The deposit should be a pure yellow ; in case it is off colour, it must be scratch-brushed with care and passed through coloured materials ; the anode conducts the electricity, and also maintains the metallic strength of the bath, but the addition of gold salt and cyanide of potassium are necessary at intervals ; when this is required is ascertained by the colour of the bath and the deposit ; when gold predominates, the deposit is blackish, and when the cyanide is in excess, the gilding takes place slowly, and is of a greyish colour. When not in use the anode must be removed, or it will be dissolved. In making solutions by the battery process, from to 2 lb. of cyanide of potassium is dissolved in each gallon of tho hot water, and two plates of sheet gold immersed ; the current from a couple of Daniell or Smee cells is passed for several hours ; the liquor may be occasionally tested to ascertain its condition with a plate of German silver, which is made to replace one of the gold plates for a short time. When satis factory, the bath may be immediately used ; it will work well if the temperature is preserved as evenly as possible from 143°-160° F. Care should be observed when making this bath to either wholly immerse the gold plates, or else to protect the portion above the surface of the liquid by means of varnish, otherwise it is liable to be cut through at the line of division.
A great deal of the colouring in clectro gilding depends upon the manner in which the curtent is regulated and the baths kept in condition, and to obtain excessive coloration rather by additions to the bath than by interference with the current or alteration of the temperature. A bath to be
used for red gilding only may be made by adding to the ordinary bath acetate of copper in crystals ground to powder, and dissolved in water or some liquid from an old electro-eopper bath. Small artiolee may be made to pass to red by heating them after they have been covered with acetate of copper, cream of tartar, and common salt. To obtain gold with a pink appearance, the articles are first gilt yellow in the ordinary way, then reddened, and then passed quickly through a silvering bath. To produce green or white gilding, add to the bath a dilute solution of nitrate of silver, less of this being required for greeu and more for white. In the general working of gilding baths, it is as well to always give inferior work, such as zinc or tin, a light deposit of copper, and the same remark holds good for steel and iron ; German silver should be gilt in very weak solutions. Vessels which require only to be gilt inside, such as cups, sugar-basins, and the like, are filled with the gilding solution with an anode of gold hung in the middle, the other wire from the battery being connected to the vessel itself ; parts which cannot he gilt conveniently in this way may be lightly ooated by a sponge or rag wetted with the solution, and dipping in it, The battery moat frequently used is either a single Smee or a Daniell.
When a gold solution which has been worked for a long time fails to yield the rich colour so necessary in electro gilding, the solution may be restored to its proper condition by evaporation to dryness. After a gilding bath has been worked for a lengthened period it is apt to yield a brownish or foxy oolour, which is due to the accumulation of organic matter, from imperfect rinsing of the work after scrateh-brushing, by which small quantities of the beer used in the operation enter the solution, and cause the deposit to assume shades of colour which are anything but desirable for superior work. Although it involves a little trouble, and occupies a certain amount of time, if the solution be evaporated to absolute dryness, then redissolved in hot water and filtered, the bath restored by this means will give admirable results. After complete evaporation and subsequent redissolving, a small amount of additional cyanide will be necessary ; and since it is probable that the solution, after long working, may contain less than its original proportion of gold, it will be advisable, after redissolving the dry mass, to use about 25 per cent. less water than would represent the original bulk of the solution.