In the majority of the methods employed, the actual proportions of the ingredients are not stated, or when stated are not to be relied upon; in every case a trial should be made on clean pieces of copper, and repeated at least once. As a rule, it will be found that the sal-ammoniac must be in excess of the other salts.
(a) To 1 pint methylated finish add 4 oz. shellac and 1/2 oz. benzoin; put the bottle in a warm place, shaking it occasionally. When the gum is dissolved, let it stand in a cool place 2-3 days to settle, then gently pour off the clear mixture into another bottle, cork it well, and keep it for finest work. The sediment left in the first bottle, by adding a sufficient quantity of spirit to make it workable, will do for the first coat or coarser work when strained through a fine cloth., Next get 1/2 lb. finely ground bronze green - the shade may be varied by using a little lampblack, red ochre, or yellow ochre; let the iron be clean and smooth, then take as much varnish as may be required, and ald the green colour in sufficient quantity; slightly warm the article to be bronzed, and with a soft brush lay on it a thin coat. When that is dry, if necessary lay another coat on, and repeat until well covered. Take a small quantity of the varnish and touch the prominent parts with it; before it is dry, with a dry pencil lay on a small quantity of gold powder and then varnish the whole.
(6) Give a superficial coating of copper by electrolysis, which can then easily be bronzed by means of an application of weak ammonia, which may be allowed to dry off, and the castings then be brushed in the prominent portions. A layer of good clear spirit-varnish greatly increases the durability of this bronzing.
(c) The finished coatings may be brushed over with a mixture of hard white varnish, and finely-ground bronze green, of an oily consistency. The castings must be slightly warmed, and be quite smooth and clean. When the first coat is dry, which soon takes place, another can be applied if required, taking care to lay on thinly each time, and to get body by repeated applications. This being satisfactorily coloured, a small quantity of gold bronze power is taken up with a dry camel-hair pencil, and the prominent edges of the work are lightly touched with another brush dipped in clear varnish; while still tacky, the bronze powder is laid on with the dry brush. Again the work is allowed to dry thoroughly, when a final thin coating of the best hard varnish is given all over.
(d) The iron to be treated is properly cleaned and dipped in a crucible of melted bronze, on which floats a covering of melted borax; it is stirred in this until it acquires the temperature of the molten mass, and becomes covered; it is then taken out and placed to cool in a hearth. Larger pieces of iron must be heated first, that they may not reduce the temperature of the molten metal too much.
This operation is to give to new metallic objects the appearance of old ones, by imitating the characteristic appearance imparted by age and atmospheric influences to the metals or metallic compounds, and especially to copper and its alloys.
(a) The most simple bronze is obtained by applying upon the cleansed object a thin paste made of water with equal parts of plumbago and iron peroxide, with a certain proportion of clay. Then heat the whole, and when the object is quite cold, brush in every direction for a long time with a middling stiff brush, which is frequently rubbed upon a block of yellow wax, and afterwards upon the mixture of plumbago and iron peroxide. This process gives a very bright red bronze, suitable for medals kept in a show case.
(6) This bronze may also be produced by dipping the article into a mixture of equal parts of perchloride and nitrate of sesquioxide of iron, and heating until these salts are quite dry. Then rub with the waxed brush as described.
(c) Cleanse the article, and cover it with ammonia hydrosulphate, which allow to dry, then brush with iron peroxide and plumbago, and afterwards with the waxed brush. If the piece impregnated with ammonia hydrosulphate is gently heated a black bronze is obtained, which being uncovered at certain places produces a good effect.
(a) Obtain a bottle of Japan gold size, a rather broad camel-hair brush, and the desired quantity and shade of bronze powder. Then, with an ordinary pig-bristle brush, give the article a coat of the Japan size to fill up the pores. When quite dry, give another coat. Let it stand until it becomes slightly sticky (not too wet or else it will drown the bronze). Then dip your camel-hair brush into the bronze, and carefully brush it over the article until completely covered, taking care to hold the work over a sheet of paper to save all the surplus bronze. The bronze is about 2s. 6d. to 3s. an oz, but 1/4 oz. goes a very great way. Some, after the above operation, cover over with mastic varnish. Of course, if they are likely to be handled, the varnish will preserve them.
(o) Prepare a soap from linseed oil boiled with caustic soda lye, to which add a solution of common salt, and concentrate it by boiling till it becomes somewhat granular upon the surface; it is then strained through a linen cloth, and what passes through is diluted with boiling water, and again filtered. Dissolve 4 parts blue vitriol and 1 part copperas separately in hot water, and add this solution to the solution of soap as long as it occasions any precipitate. This flocculent precipitate is a combination of the oxides of copper and iron with the margaric acid of the soap, the former giving a green and the latter a reddish-brown colour, the combination of the two resembling that greenish rust which is characteristic of ancient bronzes. When the precipitate is completely separated, a fresh portion of the vitriol solution is to be poured upon it in a copper pan, and boiled in order to wash it. After some time the liquid is poured off and the soap is washed with warm and afterwards with cold water, pressed in a linen bag, drained, and dried, when it is ready for use in the following manner: -
3 lb. pure linseed oil are boiled with 12 lb. finely-powdered litharge, and the mixture is straiued through a canvas cloth and permitted to stand in a warm place until it becomes clear; 15 oz. of this, 12 oz. of the above described soap, and 5 oz. of fine white wax are mixed together at a gentle heat in a porcelain basin, by means of a water bath. The mixture must be kept some time in a molten state, to expel any moisture which it may contain. It is then applied by means of a paint-brush to the surface of the gypsum, which is heated to the temperature of about 200° F. After exposure to air for a few days, the surface is rubbed with cotton wool or a fine rag, and variegated with a few streaks of metal powder or shell gold. Small objects may be dipped in the melted mixture and then exposed to the heat of the fire until thoroughly penetrated and evenly coated with it.
Bronze powders made of impalpable brass are applied upon metals to imitate bronze, and also upon articles of plaster of Paris, and ceramic wares. After the object has been cleaned, it receives a thin coat of fatty drying varnish, which is allowed to become nearly dry. The bronze powder is then laid on with a brush, and adheres strongly. After drying, cover it with a coat of transparent colourless varnish. This, process is only suited to large pieces which are imperfectly finished, and will not do for reproductions intended to respect the small details.
(a) Verdigris, 4 oz.; tutty, 2 oz.; corrosive sublimate, 1 dr.; borax, 1 dr.; nitre, 1 dr.; mix them to a paste with oil, and fuse in a crucible. The "tutty" here mentioned is sometimes called "putty" powder, and is an oxide of tin. (b) Mix together 100 parts copper sulphate, and 50 crystallised soda carbonate. Apply heat till they unite, powder the mass when cold, and add 15 parts copper filings, mix well, and keep at a white heat for 20 minutes; wash and dry the product.
Clean the castings, and wash them with a mixture of 1 part each of copper and iron sulphates in 20 parts of water; dry and wash again with a solution of verdigris, 5 parts; in distilled vinegar, 11 parts. When dry, polish with colcothar.
Make a concentrated solution of soluble glass of a strength of about 30° B. The article to be bronzed or decorated is first coated with a very thin film or layer of the solution of soluble glass, which is applied by a soft paint-brush, and the bronze or other powder is applied through a sieve; the articles are then dried, by exposure to the atmosphere or artificial heat, after which the excess of powder that has not been. absorbed by the soluble glass is removed by a brush. The bronze powder so applied will resist the effects of heat and of washing with alcohol, or of polishing by steel or agate burnishers. This is also particularly beneficial for decorating iron and porcelain stoves, inasmuch as the bronzing powder will not be affected by the heat of the stove. The gilding on the frames of pictures and lookiug-glasses when worn can also be restored in a few minutes by this process.
The zinc to be bronzed must receive an electro-deposit of brass, which is then dipped into a weak solution of copper sulphate for a red tinge. When dry, wet with a rag dipped into ammonia hydrosulphate, or a solution of potassium polysulphide, or copper proto-chloride dissolved in hydrochloric acid. After another drying, the surface is brushed over with a mixture of iron peroxide and plumbago, according to the tint desired. The brush may be slightly wetted with essence of turpentine, which aids the adhesion of the powders. The raised parts are strongly rubbed to uncover the brass. Afterwards give a coat of colourless varnish.
The most beautiful cobalt plating may be obtained upon brass and copper, by employing in the battery - with two Bunsen cells - a moderately concentrated solution of the double chloride of ammonium and cobalt. This solution is prepared by dissolving 40 grm. crystallised cobalt chloride, and 20 grm. ammonium chloride, in 100 cc. water, with the addition of 20 cc. ammonia.