moulds having deeply indented surfaces. As soon as the surface is entirely covered remove the supplementary wires. If only one face of the mould is to receive the deposit protect the other surfaces by a resist varnish, melted yellow wax, or softened gutta-percha.

Adhesive Deposits upon Metals.Metals are unequally qualified to receive the galvanoplastic deposit; and some are naturally unfit for it. For instance, wrought and cast iron, steel, and zinc, as soon as immersed in the solution of sulphate of copper, and without the aid of electricity, decompose the salt, and are coated with a muddy precipitate of copper without adherence. It is necessary to give them previously a thick coat of copper in the bath of double salts before submitting them to the action of the sulphate of copper. Tin, although presenting these inconveniences in a much less degree, should also be copper electroplated in the solutions of double salts before going into the bath. When the metal to be covered is unacted upon by the bath, cleanse it well, and submit it to the action of the current, which will give a rapid and uniform deposit; this should not be too thick, otherwise the surfaces may have a coarse appearance, which impairs the fineness of the lines of the mould. With a good bath, and a wellregulated electric current, the delicacy of the pattern will not be defaced by a copper coat having the thickness of stout writing paper. A bright lustre may be obtained by scratch-brushing or burnishing; or by a passage through aquafortis and soot, and afterwards through the compound acids for a bright lustre.

Dead Lustre Gilding by Galvanoplastic Deposit.-Adhering galvanoplastic deposits give a very cheap and handsome gilding with a dead lustre, which, although not equal in durability, has the appearance of that obtained with mercury, already described. Having cleansed the mould if metallic, or rendered it a conductor if non-metallic, immerse it in the solution of sulphate of copper, and allow the deposit to acquire a dead lustre slightly in excess of that desired. After this operation, which may last from 2

to 6 hours, remove the article from the bath, rinse it in plenty of water, and pass it rapidly through the compound acids for a bright lustre, which diminish the previous dulness of the appearance. Next rinse in fresh water; steep in a mercurial solution similar to that employed for gilding by dipping; rinse again; and immerse in an electro-gilding bath made of;-Distilled water, 2 galls.; phosphate of soda, 21 oz.; bisulphite of soda, 3 oz.; cyanide of potassium, of an

ounce; gold, for neutral chloride, of an ounce. At first, the current is rendered sufficiently intense by dipping the platinum anode in deeply; afterwards the intensity is diminished by partly withdrawing the anode until the entire shade of gold is obtained. This gilding requires but little gold, as the frosty dead lustre comes from the copper. When the lustre of the copper is very fine and velvety, dispense with the dipping into the compound acids, but the rapid passage through the mercurial solution is always desirable. If the deposited gold

not uniform, or appears cloudy, it is proof of an imperfect deposit in the bath, or of an insufficient steeping in the compound acids. The piece should then be removed from the bath, washed in a tepid solution of cyanide of potassium, rinsed in fresh water, dipped in the solution of nitrate of binoxide of mercury, and electro-gilded anew. This gilding bears burnishing well; avoid acid waters and soap, which will produce a red polish, and use only the fresh solutions of linseed, or of marsh-mallow root. The tone of gold thus obtained is richer, deeper, and more durable than that produced upon frosted silver, the latter being recognized by the green colour of the burnished parts. This kind of deposit may be employed for binding substances together, because the covering coat will be continuous.

Galvanoplastic Deposits without Adhesion. After thoroughly cleaning the pattern, rub it with a brush charged with plumbago, or with a soft brush slightly greased by a tallow candle. The film of fatty substance should not be seen at all. The deposit obtained

represents an inverted image of the pattern, and the raised parts become hollow. Remove the mould, and perform the same operation upon the deposit, and this second deposit is the accurate reproduction of the first pat

tern.

DEPOSITS UPON NON-METALLIC SUBSTANCES. By this process porcelain, crystal, plaster of Paris, wood, flowers, fruits, animals, and the most delicate insects may be coated. These substances have no conductive power for electricity; it is, therefore, necessary to metallize them.

Metallization.-This coat should be so thin as not to alter the shape or the minutest parts of the model.

Plumbago, or graphite, is generally preferred, and in most cases its conducting power is sufficient; and it may be applied in films thin enough not to impair the sharpness of the mould. The plumbago found in the trade is rarely pure. Remove the impurities by digesting for 24 hours a paste made of plumbago and water, with hydrochloric acid. Several washings with water, and slow drying in a stove, finish the operation. If the plumbago is in large lumps, it should be powdered and passed through a silk sieve. The conducting power of this substance is sufficient when the surfaces are not deeply indented; but the mould should be rough enough for the plumbago to stick to it.

of an

Gilt Plumbago has a conducting power much greater than that of the ordinary substance. Prepare as follow;-In 1 pint of sulphuric ether dissolve ounce of chloride of gold, and thoroughly mingle with it from 18 to 20 oz. of good plumbago. Then pour into a shallow porcelain vessel, and expose to the action of air and light. After a few hours the ether completely volatilizes; stir the powder now and then with a glass spatula. Finish the drying in a stove.

Silvered Plumbago.-Dissolve 3 oz. of crystallized nitrate of silver in 3 pints of distilled water; mix this solution with 2 lbs. of good plumbago. Dry in a porcelain dish, and then calcine at a red heat in a covered crucible. After cool

ing, powder and sift. Plumbago thus metallized conducts electricity nearly as well as a metal, although it is very expensive. Bronze powder mixed with plumbago is also used.

Rendering Moulds Impervious to Liquids. Porous substances, before being coated with plumbago, are submitted to a previous operation, to render them impervious, by covering them with a coat of varnish, or by saturating them with wax, tallow, or stearine. For instance, with a plaster cast, cut a groove on the rim of the mould, place in it a brass wire, twist the ends, which must be long enough to hold the cast by. The cast, having been previously dried, is then dipped into a bath of stearine kept at a temperature of from 180° to 212° Fahr., and a number of bubbles of air will escape from the mould to the surface. When the production of air-bubbles is considerably diminished, remove the cast from the bath. When the cast is tepid, cover it with powdered plumbago, and let it get quite cold. Then, after breathing upon it, rub thoroughly with a brush covered with plumbago; and be careful that the surfaces are completely black and bright, without grey or whitish spots. When the mould is very undercut, it is difficult to employ plumbago. In such cases metallize the whole, or the deep parts only, by the wet way. Soft brushes should not be used for rubbing plumbago. When the substances to be metallized are not porous, such as glass, porcelain, stoneware, horn, and ivory, cover them with a thin coat of varnish, which, when nearly dry, receives the plumbago.

Metallization of Ceramic Articles.After having varnished the portions of the piece to be coppered, cover them with very finely laminated foils of lead, which bend to all desired shapes; then connect a brass conducting wire with the lead, and dip the whole into the bath; copper is immediately deposited upon the metallic parts. Thus glass vases may be entirely covered with copper, upon which deposit layers of gold or silver. The chaser may penetrate with his tool to different depths,

Solution of Phosphorus in Bisulphile of Carbon.-Half fill a glass stoppered bottle with a large neck with bisulphide of carbon, then gradually introduce the phosphorus gently dried with blotting paper, and shake the bottle now and

Metallization by the Wet Way.-Silver, gold, and platinum, reduced from their solutions, have an excellent conducting power. Silver is generally preferred, and its nitrate is dissolved in certain liquids, variable with the substances to be covered. Apply the solution with a pencil upon the mould, and let it dry; repeat the operation two or three times. Lastly, expose the mould to the action of the sunlight, or of hydrogen, or fix it to the top of a box which closes hermetically, and at the bottom of which is a porcelain dish holding a small quantity of a concentrated solution of phosphorus in bisulphide of carbon. After a few hours this solution completely evaporates, and reduces to the metallic state the nitrate of silver covering the mould, which becomes black, and is then ready for the bath. When used to metallize wood, porcelain, and other resisting substances, dissolve 1 part of nitrate of silver in 20 parts of distilled water. With fatty or resinous materials, which water will not wet, use aqua ammonia. With very delicate articles, which will not bear a long manipulation, make the solution in alcohol, which evaporates rapidly. Concentrated alcohol dissolves nitrate of silver but slightly; but enough will be dissolved for metallizing flowers, leaves, and similar articles, if the solution is aided by grinding in a mortar. If the conducting wire is fixed to the mould before the metallization, the wire must be of gold, silver, or platinum, as

then.

Phosphorus is added until no more dissolves. This preparation requires great care in the handling, because in drying upon combustible materials it takes fire spontaneously.

Plaster of Paris Moulds.-After the original model, say a medal, has been thoroughly rubbed with soap or plumbago, wrap round the rim a piece of stout paper, or thin lead foil, and bind it in such a manner that the article to be copied, face upwards, is at the bottom of the box thus formed. Then in a vessel filled with a sufficient quantity of water, sprinkle fine plaster of Paris until the last portions reach the level of the water. After waiting for one or two minutes, stir, and the thin resulting paste must be employed immediately. With a painter's brush give a thin coat of this paste, and press into all the recesses; this is to expel the air; then pour the remainder of the paste up to a proper height, and allow it to set. After a few minutes the plaster hardens, and may be separated from the paper. Scrape off what has run between the paper and the rim of the medal, and the plaster cast will separate from the model. Plaster of Paris moulds cannot be introduced into the bath without having been previously rendered impervious.

Moulding with Stearine and Wax.Stearine is melted and poured upon the model when it is going to set. When stearine is too new or dry, it crystallizes in cooling, and this impairs the beauty of the cast. In such case it should be mixed with a few drops of olive oil, or with tallow, or suet; if it is made too fat, it will remain soft and difficult to separate from the mould. It should then be mixed with virgin wax or sper

maceti. As stearine contracts consider- | ably by cooling, its employment must be avoided when the copies are required to be perfectly accurate. When it is desired to make a cast with stearine of a plaster model, the latter should be thoroughly saturated with water or stearine beforehand, and should also be perfectly coated with plumbago before the melted substance is poured upon it, otherwise the two will stick together, and it will not be possible to separate the cast from the model. Wax may also be employed in the same manner, but its price and want of hardness interfere with its application.

Moulding with Fusible Metal.-This metal is a perfect conductor of electricity, and therefore well adapted to the production of homogeneous deposits of equal thickness; it is, however, seldom employed, on account of the difficulty of the operation, of its crystalline texture, and of the presence of air-bubbles. 1. Pure lead, 2 parts in weight; tin, 3; bismuth, 5; fusible at 212° Fahr. 2. Pure lead, 5 parts in weight; tin, 3; bismuth, 8; fusible from 180° to 190° Fahr. 3. Pure lead, 2 parts in weight; tin, 3; bismuth, 5; mercury, 1; fusible at 158° Fahr. 4. Pure lead, 5 parts in weight; tin, 3; bismuth, 5; mercury, 2; fusible at 125° Fahr. For those alloys without mercury, the component metals may be melted together; when mercury is employed, it should be added when the three other melted metals have been removed from the fire. To obtain a thorough mixture the alloy should be stirred with an iron rod, or melted over and cast several times. 1. Run the metal into a small dish, remove the oxide with a card, and then apply the model, give it a few taps when the setting takes place; or put the model into the dish, and pour the clean alloy upon it. 2. Put the medal at the bottom of a small box of iron or copper, and bury half of its thickness in plaster of Paris; then, cover the medal with the cold fusible alloy, and apply heat until it is melted, when it is allowed to cool off. It is easy to separate the medal from the fusible alloy, as the portion protected by the plaster of

Paris may then be grasped. A well-made cast of fusible alloy is the best mould for galvanoplastic operations with silver and gold. Alloys containing mercury should not be used for taking casts from metallic medals, iron excepted, which would be amalgamated and injured. Copper deposits obtained upon such alloys are very brittle. Melted sulphur produces very neat and sharp casts; it is, however, very difficult to get it metallized, and it transforms the deposit of copper into sulphide.

Moulding with Gelatine.-In certain conditions, the elasticity of gelatine and gutta-percha allows of removing them from undercut or highly-wrought parts, and they reacquire the shape and position they had before the removal. This property is found in gelatine to a higher degree than in gutta-percha, but it requires a very rapid deposit, otherwise it will swell and be partly dissolved by too long an immersion in the solution of sulphate of copper. Put a sufficient quantity of colourless plates of gelatine in cold water, and let it swell there for about 24 hours; then drain off the water, and heat the gelatine upon a water bath until it has become of a syrupy consistency; it is then ready to be poured upon the object, which must be encased in a box of pasteboard or of thin lead. After cooling for about 12 hours, separate the cast from the object. To enable the gelatine to remain longer in the bath without alteration, use one of the following mixtures;-1. Dissolve the best gelatine in hot water, and add

th of the weight of gelatine in tannic acid and the same quantity of rock candy; then mix the whole thoroughly, and pour upon the model in its box. After a few hours the gelatine may be easily separated from the object. 2. A mould having been made with gelatine alone, pour on it a solution of water holding 10 per cent. of bichromate of potash, and after draining, expose the mould to the action of the sun. 3. Beat, in 2 pints of distilled water, the whites of 3 eggs, filter, and cover the entire surface of the gelatine mould with this liquid. After drying, operate with the