Many castings are liable to be spoiled through deficiency of metal; this can always be obviated by taking a known bulk or weight of modelling wax for the work, and weighing the remainder after the work is done. A little simple calculation will enable the correct quantity of metal to be ascertained, and an allowance of about 25 per cent, additional will cover all necessary for gate, riser, and vents. (Thps. Fletcher )
(c) The Japanese are the real authorities to whom we must turn for guidance in the use and treatment of alloys, both in texture and colour. First, as regards texture, they seem to delight in copying in metal-work the most delicate texture; even the bloom on the surface of fruit is not beyond their admirable skill. In tracing the nature of their methods, it is necessary to repeat what has often been said respecting the alloys they employ in order to produce their wonderful results. There is a wide range of such alloys, but the principal of them are but few. There is an alloy of silver and copper, sometimes with, equal proportions of precious and base metal, and there are endless varieties of copper of different degrees of purity. There are several kinds of brass. They have also a remarkable series of alloys, in which the precious metal replaces the tin and zinc of ordinary bronze; but really their main alloys, with the exception of bronze, are comprised in the following examples.
The first is called shaku-do; it contains: -
(a) Copper • • • •
Silver . • .
Gold • • • •
Iron and Arsensic .
(b) Copper • . • •
Silver • • • •
Gold . • • •
or in addition to about 95 per cent, of copper, as much as 4 per cent, of gold. It has been used for very large works. Colossal statues are made of it, one cast at Nara in the 7th century being specially remarkable. The quantity of gold is, however, very variable, and certain specimens contain only 1.5 per cent, of the precious metal. The next important alloy used by the Japanese is called shibu-ichi: -
(c) Copper ..
(d) Copper . . .
There are many varieties of it, but in both these alloys, shaku-do and shibu-ichi the point of interest is that the precious metals are, as it were, sacrificed in order to produce definite results, gold and silver, when used pure, being employed very sparingly to heighten the general effect. In the case of shaku-do, the gold appears to enable the metal to receive a beautiful rich purple coat or patina when treated with certain pickling solutions, while shibu-ichi possesses a peculiar silver-grey tint of its own, which, under ordinary atmospheric influences, becomes very beautiful, and to which the Japanese artists are very partial. These are the principal alloys, but there are several varieties of them, as well as combinations of shaku-do and shibu-ichi in various proportions, as, for instance, in the case of kiu-shibu-ichi, the composition of which would correspond to one part of shaku-do rich in gold, and two parts of shibu-ichi rich in silver.
Pickling solutions are made up respectively in the following proportions, and are used boilinz: -
438 gr. .
Sulphate of copper .
87 gr. ., .
. • •
5 fl. dr.
That most widely employed is (e). When boiled in (g) solution, pure copper will turn a brownish red, and shaku-do, which contains a little gold, becomes purple. Very small quantities of metallic impurity affect the colour resulting from the action of the pickle. Copper containing a small quantity of antimony gives a shade very different from that resulting from the pickling of pure copper. But the copper produced in Japan is often the result of smelting complex ores, and the methods of purification are not so perfectly understood as in the West. The result is that the so-called " antimony " of the Japanese art metal workers, which is present in the variety of copper called kuromi, is really a complex mixture containing tin, cobalt, and many other metals, so that a metal-worker has an infinite series of materials at command with which to secure any particular shade; and these are used with much judgment, although the scientific reasons for the adoption of any particular sample may be hidden from him.
It is strictly accurate to say that each particular shade of colour is the result of minute quantities of metallic impurity.
The action of these solutions is remarkable. You have copper to which a small amount of silver and a small amount of gold are added. The amount of gold may be variable, and artificers often take credit for putting in much more than analysis proves to be present; but a small amount of gold, it may be only 1. per cent., is sufficient to entirely change the character of the copper, and when you come to treat it by pickling solutions, you get a totally different result from what you would if copper alone were employed. The Japanese also take copper and dilute it, sometimes half copper and half silver, sometimes only about one-third silver and all the rest copper, and that gives the lovely series of grey alloys which, either by exposure to atmospheric influences, by handling, or by treatment of suitable pickles, gives the beautiful series of light and dark greys of which the Japanese are so particularly fond, and to which the name of shibu-ichi is given. Then, again, they have copper in which small amounts of impurities may be present, and the nature of such impurity and its amount, which seldom exceeds -jjjth per cent., is quite sufficient to change the character of the copper.
The Japanese, working in no small measure by rule of thumb, find that certain varieties of copper are best suited for definite processes, and they store them up and use them in a definite way.
In all these cases the precious metals are deliberately sacrificed with a view to produce a definite result. Why cannot we use the alloys (of which we have the analyses) in order to produce results in these lovely grey tints ? The finest piece of shaku-do that I know, with its blue bloom, is a beautifully-carved sword hilt from the collection of Mr. Edward Dillon; and shaku-do forms the basis of many specimens of Japanese art. In a little medicine case, the base is shaku-do, nearly of the composition given in Analysis No 1. The enrichments are the grey shibu-ichi, a kuromi fish, with 24 tiny dots of gold in the space of about one-eighth of an inch. Then there is a shibu-ichi shell, with a gold shell placed beside it, and a kuromi carrot, on which a grey shibu-ichi mouse, with shaku-do spots let into him, is feeding. All this lavish adornment is most perfectly done. The actual method of manipulation I will now describe.