will distinguish them. It is impossible to describe the effect produced by these mixed tints, which can be remembered only after having been seen.

Some time ago, the various shades of pink were obtained by gilding in the following bath at different temperatures, and with currents of variable intensity, the articles already yellow-gilded by battery, or by immersion. This bath was composed of

New silvering bath

Hot gilding bath (new)

New coppering bath

1 part.

25 parts.

15

66

This formula has no regularity in its working, and may give to a first batch of articles a white color, to the second a red, and to the third a dull, dark shade.

At the present time the following methods are used:The articles are first yellow-gilded by the formula of the immersion bath of pyrophosphate, or by that of the hot electro-bath. Then, without drying, but keeping them in fresh water, they are made into small lots or packages weighing about 1 or 2 ounces each, which are lightly passed through the quicking bath, and then red gilded, hot, either in an old and nearly spent electro-bath in which a great deal of copper has already been gilded, or in a new bath composed of ten parts of hot electrogilding bath (first formula, Chapter XXI. p. 200), and three to four parts of the electro-coppering solution (first formula, Chapter X. p. 118).

According as the electric current is more or less intense, so will the gilding be more or less red. For imparting to it the pale tint of many articles gilded by the use of amalgam (see Chapter XVII.), the red gilding is passed through a boiling and nearly spent bath of pyrophosphate, to which has been added one-tenth, or a twentieth, or a thirtieth of its volume of a silver bath, or simply a

few drops of a concentrated solution of nitrate of silver. A few gilders simply pass their red gilding through a cold bath for silvering by dipping. In whatever manner we operate, a blush of silver is deposited upon, and whitens, more or less, the red gilding.

This gilding should be scratch-brushed, or, preferably, burnished, and it then imitates gilding by mercury or jeweller's alloy. It may be chased, but then the lustre soon disappears, on account of the large proportion of copper it contains.

In case of failure to obtain the proper pink gilding, which often happens, it is sufficient to plunge the articles for a few seconds into a mixture composed of five parts of sulphuric acid to one of nitric acid. The copper and silver are dissolved, and the yellow gilding reappears, which the operation may be begun anew.

upon

ADDITIONAL FORMULÆ.

Günther recommends (Winckler, Handb. d. Metallüberzügen, 175) the following baths for electro-gilding,

viz:

For yellow gold, he prepares a neutral chloride of gold, in the usual manner, and prepares a bath having the following proportions:

Chloride of gold .

Ferrocyanide of potassium (fused)
Water.

25 parts.

60 to 80 66

3000 66

This is boiled about a quarter of an hour, and then diluted to double its volume with water, boiled again, allowed to cool, and filtered.

For red gold, he proposes the addition of some metallic copper to the acid mixture used in dissolving the gold; the bath is then prepared as above; or he adds to the

gilding bath, prepared as above, a sufficient quantity of a

For green gold, he adds a small quantity of silver to the acid mixture while the gold is dissolving; or uses, as an addition to the bath prepared as above, a suitable quantity of a solution composed of

Briant prepares a gilding solution by treating a warm solution of chloride of gold with an excess of magnesia, by which the gold is precipitated as oxide. The precipitate is filtered, washed, and digested with water containing about 8 per cent. of nitric acid, which dissolves out the magnesia, leaving the gold oxide, which should be repeatedly washed until it shows no acid reaction when tested with test paper. He dissolves the oxide, resulting from the treatment of 3 parts of gold in the manner just described, in a solution composed of

This solution is boiled for 20 minutes, and the small amount of precipitated iron is removed by filtration. The resulting golden-yellow liquid forms the gilding bath, and may be used either hot or cold.

Elsner's solution (Winckler, Handb. d. Metallüberzügen) is prepared in substantially the same manner.

Braun (Winckler, Handb. d. Metallüberzügen, 172) prepares a hot electro-gilding bath with fulminate of gold resembling the first formula for "cold electro-gilding

The

baths" (Chapter XX. page 191), but more dilute. He prefers to use it at a temperature of from 100° to 140° Fahr., and with a moderately strong current. His directions for preparing the bath are substantially as follows: He prepares a neutral chloride of gold in the usual manner, and adds to the solution common salt, in the proportion of 3 parts of salt to each 10 parts of gold; then evaporates to dryness, and cautiously fuses the resulting double chloride to drive off the excess of acid. fused salt on cooling is dissolved in distilled water, and treated with ammonia in excess, whereby gold fulminate is precipitated. This is filtered and washed with water until the last portions of the wash water are tasteless. The still moist fulminate of gold is then dissolved in cyanide of potassium, and the solution diluted with water, so that the liquid shall contain in 1000 parts 15 parts of gold. The liquid is now boiled until all the ammonia has been driven off (that is, until it no longer smells of ammonia), and is then further diluted with water, so that 2000 parts of solution shall contain 15 parts of gold. Braun uses this bath chiefly for electro-gilding articles of Germansilver; it is affirmed to produce a fine dead gilding.

Gore notices (Electro-metallurgy, 138) that a very rich dead gilding may be obtained in a cyanide solution by adding a little wet aurate of ammonia (i. e., fulminate of gold) to the liquid, just before gilding; and a clear, bright yellow gilding by adding to an ordinary cyanide gilding solution a small quantity of caustic soda; and that copper and brass trinkets that require to have a "dead" gilded appearance, may be dipped for this purpose before gilding in a mixture of equal parts of sulphuric and nitric acids, to which a little common salt has been added.

For a half-dead and dead gilding, Messrs. Christofle & Co., of Paris, employ a cyanide solution, in combination

with the Elkington bath. The solution is worked at a temperature of from 65° to 85° Fahr. with a gold anode. For half-dead effect (Winckler, Handb. d. Metallüberzügen, 174), they convert 31 parts of gold into chloride, add thereto 1960 parts cyanide of potassium solution (of 25° B.), and 840 parts of caustic potassa solution of same density; the mixture is then boiled until the solution marks 35° B.

This solution is mixed with the Elkington bath, composed of 150 parts gold chloride, 9000 parts bicarbonate of potassium, and 30,000 parts of water, boiled for two hours. The articles to be gilded are not previously coppered.

For dead gilding, they dissolve 31 parts of moist fulminate of gold in 1000 parts of distilled water, containing 250 parts of cyanide of potassium, and add thereto 4500 parts of a ferrocyanide of potassium solution of 30° B. strength. The resulting solution is boiled for about half an hour, and is then ready. It may be worked either cold or warm, and the articles are not previously coppered.

Becquerel recommends (Gore, Electro-Metallurgy, 133) a solution made of 1 part of gold chloride, and 10 of ferrocyanide of potassium in 100 parts of water, to which, after filtering, to remove separated iron, 100 parts of a saturated solution of ferrocyanide of potassium is added, after which an equal or double volume of water is also added. The color of the gilding will depend on the concentration of the bath; the best effect is had with the most dilute baths, and with those most free from iron. Washing the articles in diluted sulphuric acid, and rubbing gently with a piece of linen cloth brightens the gilding.

Levol (Id. 133) dissolves neutral gold chloride in water, and adds enough of an aqueous solution of sulpho-cyanide of potassium to redissolve the precipitate at first formed.