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Gilding, Silvering and Tinning

a portion of alloy, of the same size as the ingots | of metal, and of suitable thickness. Having placed a piece of gold upon an ingot intended to be plated, he hammers and compresses them both together, so that they may have their surfaces as nearly equal to each other as possible; and then binds them together with wire, in order to keep them in the same position during the process required to attach them. Afterwards he takes silver-filings which he mixes with borax to assist the fusion of the silver. This mixture he lays upon the edge of the plate of gold, and next to the ingot of metal.

Having thus prepared the two bodies, he places them on a fire in a stove or furnace, where they remain until the silver and borax placed along the edges of the metals melt, and until the adhesion of the gold with the metal is perfect. He then takes the ingot carefully out of the stove. By this process the ingot is placed with gold, and prepared ready for rolling into sheets.

To Silver Copper Ingots.

The principal difficulties in plating copper ingots are, to bring the surfaces of the copper and silver into fusion at the same time; and to prevent the copper from scaling; for which purposes fluxes are used. The surface of the copper on which the silver is to be fixed must be made flat by filing, and should be left rough. The silver is first annealed, and afterwards pickled in weak muriatic acid: it is planished, and then scraped on the surface to be fitted on the copper. These prepared surfaces are anointed with a solution of borax, or strewed with fine powdered borax itself, and then confined in contact with each other, by binding wire. When they are exposed to a sufficient degree of heat, the flux causes the surfaces to fuse at the same time, and after they become cold they are found firmly united.

Copper may likewise be plated by heating it, and burnishing leaf-silver upon it; so may iron and brass. This process is called French-plating.

Grecian Gilding.

Equal parts of sal-ammoniac and corrosive sublimate, are dissolved in spirit of nitre, and a solution of gold made with this menstruum. The silver is brushed over with it, which is turned black, but on exposure to a red heat, it assumes the color of gold.

To Dissolve Gold in Aqua Regia.

Take an aqua regia, composed of 2 parts of nitric acid, and 1 of muriatic acid; let the gold be granulated, put into a sufficient quantity of this menstruum, and exposed to a moderate degree of heat. During the solution an effervescence takes place, and it acquires a beautiful yellow color, which becomes more and more intense, till it has a golden or even orange color. When the menstruum is saturated, it is very clear and transparent. To Gild, by Dissolving Gold in Aqua Regia.

Fine linen rags are soaked in a saturated solution of gold in aqua regia, gently dried, and afterwards burnt to tinder. The substance to be gilt must be well polished; a piece of cork is first dipped into a solution of common salt in water, and afterwards into the tinder, which is well rubbed on the surface of the metal to be gilt, and the gold appears in all its metallic lustre.

Amalgam of Gold in the large way.

A quantity of quicksilver is put into a crucible or iron ladle, which is lined with clay and exposed to heat till it begins to smoke. The gold to be mixed should be previously granulated, and heated red hot, when it should be added to the quicksilver, and stirred about with an iron rod till it is perfectly dissolved. If there should be any superfluous mercury, it may be separated by passing it through clean soft leather; and the remaining amalgam will have the consistence of butter, and contain about 3 parts of mercury to 1 of gold.

To Gild by Amalgamation.

The metal to be gilt is previously well cleaned on its surface, by boiling it in a weak pickle, which is a very dilute nitrous acid. A quantity of aquafortis is poured into an earthen vessel, and quicksilver put therein; when a sufficient quantity of mercury is dissolved, the articles to be gilt are put into the solution, and stirred about with a brush till they become white. This is called quicking. But, as during quicking by this mode, a noxious vapor continually arises, which proves very injurious to the health of the workman, they have adopted another method, by which they, in a great measure, avoid that danger. They now dissolve the quicksilver in a bottle containing aqua-fortis, and leave it in the open air during the solution, so that the noxious vapor escapes into the air. Then a little of this solution is poured into a basin, and with a brush dipped therein, they stroke over the surface of the metal to be gilt, which immediately becomes quicked. The amalgam is now applied by one of the following methods, viz: 1st. By proportioning it to the quantity of articles to be gilt, and putting them into a white hat together, working them about with a soft brush, till the amalgam is uniformly spread.

Or, 2dly. By applying a portion of the amalgam upon one part, and spreading it on the surface, if flat, by working it about with a harder brush.

The work thus managed is put into a pan, and exposed to a gentle degree of heat; when it becomes hot, it is frequently put into a hat, and worked about with a painter's large brush, to prevent an irregular dissipation of the mercury, till at last the quicksilver is entirely dissipated by a repetition of the heat, and the gold is attached to the surface of the metal. This gilt surface is well cleaned by a wire brush, and then artists heighten the color of the gold by the application of various compositions, this part of the process is called coloring.

Silvering Powders.

For silvering copper, covering the worn parts of plated goods, etc. 1. Nitrate of silver, common salt, each 30 grs.; cream of tartar, 3½ drs. Mix. Moisten with cold water and rub on the article to be silvered. 2. Pure silver (precipitated from the nitrate by copper), 20 grs.; alum 30 grs.; cream of tartar, 2 drs.; salt, 2 drs. 3. Precipitated silver, oz.; common salt, sal ammoniac, each 2 oz.; corrosive sublimate, 1 dr.

Make into a paste with water. Copper utensils are previously boiled with cream of tartar and alum, rubbed with this paste made red hot and afterwards polished. 4. Nitrate of silver, 1 part; cyanide of potassium, 3 parts; water enough to make a paste. Removing Silver from Injured Plated Ware.

Among the many branches of manufacturing at Nuremberg, in Germany, that of metals into various articles has obtained considerable importance. They include silver-plated ware of different styles and quality; which necessarily produce large quantities of spoiled materials and clippings, the recovery of which has hitherto been very imperfectly accomplished; thus causing annually a considerable loss. The reason of it was, the want of a method by which the silver might be removed without much expense, and the copper thus forced from its coating used again. give the silver a proper body. 2. By the use of a solder; slips of thin solder are placed between the iron and silver, with a little flux, and secured together by binding wire. It is then placed in a clear fire, and continued in it till the solder melts; when it is taken out, and on cooling is found to adhere firmly.

Repeated experiments have led to a very simple | till a sufficient number of leaves are applied, to process, by the action of concentrated nitric acid on silver and copper when present together. If these metals are placed into common commercial acid, (sp. gr. 1.47) they will both be strongly acted on; but a separation of the two is unattainable, since the copper, so long as any remains undissolved, will precipitate the silver from its solution by galvanic action. Nitric acid of the highest specific gravity (1.5), however, acts on the silver, but not on the copper; it renders the copper more elcctro-negative than before, less oxidizable, and deprives it of the property of decomposing the acid, and precipitating the silver.

To produce this passive condition of copper, it is not absolutely necessary to employ directly acid of that specific gravity; for any concentrated nitric acid can be made to answer the purpose by the addition of a sufficient quantity of the oil of vitriol, which deprives it of a portion of its water, and thus contributes to make it stronger. A mixture of one volume of nitric acid (sp. gr. 1,47) and six of vitriol does not dissolve copper at the temperature of boiling water; but with a smaller proportion of sulphuric acid, evolution of nitrous acid takes place. The same end and much cheaper, is obtained by employing a mixture of oil of vitriol and nitrate of soda, which are the materials used in the practice. The following is the method now generally employed: Oil of vitriol, together with five per cent. of nitrate of soda, is heated in a cast-iron boiler; or better, a stoneware pan, to 212° Fahr. The silver-plated clippings are placed in a sheet-iron bucket or colander, which is fastened to a pulley that may be moved about in the acid. As soon as the silver is removed, the colander is raised, allowed to drain, then immersed in cold water and emptied, to be again used in the same manner. When the acid-bath is fresh, the desilvering proceeds very rapidly, and even with heavy plated ware takes but a few minutes; with the gradual saturation of the bath more time is required, and it is readily perceived when the acid must be renewed. The small amount of acid solution adhering to the copper, precipitates its silver when brought into the water. To obtain its complete removal, the clippings, when raised from the desilvering bath and before immersion in water, may be dipped into a second bath prepared in the same manner, which is afterwards to be used in place of the first.

The saturated bath, on cooling, congeals to a crystalline semi-fluid mass of sulphate of copper and of soda. The silver is removed by chloride of sodium, which is added in small portions at a time, while the solution is yet warm. The chloride of silver separates readily, and is washed and reduced in the usual manner. The acid solution contains but a very small portion of copper, hardly enough to pay for recovering.

Another Method.

This process is applied to recover the silver from the plated metal, which has been rolled down for buttons, toys, etc., without destroying any large portion of the copper. For this purpose, a menstruum is composed of 3 lbs. of oil of vitriol, 1½ oz. of nitre, and 1 lb. of water. The plated metal is boiled in it till the silver is dissolved, and then the silver is recovered by throwing common salt into the solution.

To Plate Iron.

Iron may be plated by three different modes. 1. By polishing the surface very clean and level with a burnisher, and afterwards by exposing it to a blueing heat, a leaf of silver is properly placed and carefully burnished down. This is repeated 3. By tinning the iron first, and uniting the silver by the intermedia of slips of rolled tin, brought into fusion in a gentle heat.

To Heighten the Color of Yellow Gold.

Take of saltpetre, 6 oz.; green copperas, 2 oz.; white vitriol and alum, of each, 1 oz.

If it be wanted redder, a small portion of blue vitriol must be added. These are to be well mixed, and dissolved in water as the color is wanted.

To Heighten the Color of Green Gold.

Take of saltpetre, 1 oz. 10 dwts.; sal ammoniac, 1 oz. 4 dwts.; Roman vitriol, 1 oz. 4 dwts.; verdigris, 18 dwts. Mix them well together and dissolve a portion in water, as occasion requires.

The work must be dipped in these compositions, applied to a proper heat to burn them off, and then quenched in water or vinegar.

To Heighten the Color of Red Gold.

To 4 oz. of melted yellow wax, add, in fine powder, 1½ ox. of red ochre, 1½ oz. of verdigris, calcined till it yield no fumes, and oz. of calcined borax; mix them well together. It is necessary to calcine the verdigris, or else by the heat applied in burning the wax, the vinegar becomes so concentrated as to corrode the surface, and make it appear speckled.

To Separate Gold from Gilt, Copper and Silver.

Apply a solution of borax, in water, to the gilt surface, with a fine brush, and sprinkle over it some fine powdered sulphur. Make the piece redhot, and quench it in water. The gold may be easily wiped off with a scratch-brush, and recovered by cupellation. Gold is taken from the surface of silver by spreading over it a paste made of powdered sal ammoniac, with aqua-fortis, and heating it till the matter smokes, and is nearly dry, when the gold may be separated by rubbing it with a scratchbrush.

To Tin Copper and Brass.

Boil 6 lbs. of cream of tartar, 4 galls. of water, and 8 lbs. of grain-tin, or tin shavings. After the materials have boiled a sufficient time, the substance to be tinned is put therein and the boiling continued, when the tin is precipitated in its metallic form. To Tin Iron or Copper-plate.

Iron which is to be tinned is first steeped in acid materials, such as sour whey, distillers' wash, etc., then scoured and dipped in melted tin, having been first rubbed over with a solution of sal ammoniac. The surface of the tin is prevented from calcining by covering it with a coat of fat. Copper vessels must be well cleansed, and then a suf ficient quantity of tin with sal ammoniac is put therein and brought into fusion, and the copper vessel moved about. A little resin is sometimes added. The sal ammoniac prevents the copper from scaling, and causes the tin to be fixed wherever it touches. To prepare the Leaden Tree.

Put oz. of the sugar of lead, in powder, into a clear glass globe or wine decanter, filled to the bottom of the neck with distilled water and 10 drops of nitric acid, and shake the mixture well.