Part 411

«Silver»

«Antique Silver» (see also Plating).—Coat the polished silver articles with a thin paste of powdered graphite, 6 parts; powdered bloodstone, 1 part; and oil of turpentine. After the drying take off the superfluous powder with a soft brush and rub the raised portions bright with a linen rag dipped in spirit. By treatment with various sulphides an old appearance is likewise imparted to silver. If, for example, a solution of 5 parts of liver of sulphur and 10 parts of ammonium carbonate are heated in 1 quart of distilled water to 180° F., placing the silver articles therein, the latter first turn pale gray, then dark gray, and finally assume a deep black-blue. In the case of plated ware, the silvering must not be too thin; in the case of thick silver plating or solid silver 1 quart of water is sufficient. The colors will then appear more quickly. If the coloring is spotted or otherwise imperfect dip the objects into a warm potassium cyanide solution, whereby the silver sulphide formed is immediately {640} dissolved. The bath must be renewed after a while. Silver containing much copper is subjected, previous to the coloring, to a blanching process, which is accomplished in a boiling solution of 15 parts of powdered tartar and 30 parts of cooking salt in 2 pints of water. Objects which are to be mat are coated with a paste of potash and water after the blanching, then dry, anneal, cool in water, and boil again.

«Imitation of Antique Silver.»—Plated articles may be colored to resemble old objects of art made of solid silver. For this purpose the deep-lying parts, those not exposed to friction, are provided with a blackish, earthy coating, the prominent parts retaining a leaden but bright color. The process is simple. A thin paste is made of finely powdered graphite and oil of turpentine (a little bloodstone or red ocher may be added, to imitate the copper tinge in articles of old silver) and spread over the whole of the previously plated article. It is then allowed to dry, and the particles not adhering to the surface removed with a soft brush. The black coating should then be carefully wiped off the exposed parts by means of a linen rag dipped in alcohol. This process is very effective in making imitations of objects of antique art, such as goblets, candlesticks, vessels of every description, statues, etc. If it is desired to restore the original brightness to the object, this can be done by washing with caustic soda or a solution of cyanide of potassium. Benzine can also be used for this purpose.

«Blanching Silver.»—I.—Mix powdered charcoal, 3 parts, and calcined borax, 1 part, and stir with water so as to make a homogeneous paste. Apply this paste on the pieces to be blanched. Put the pieces on a charcoal fire, taking care to cover them up well; when they have acquired a cherry red, withdraw them from the fire and leave to cool off. Next place them in a hot bath composed of 9 parts of water and 1 part of sulphuric acid, without causing the bath to boil. Leave the articles in for about 1 hour. Remove them, rinse in clean water, and dry.

II.—If the coat of tarnish on the surface of the silver is but light and superficial, it suffices to rub the piece well with green soap to wash it thoroughly in hot water; then dry it in hot sawdust and pass it through alcohol, finally rubbing with a fine cloth or brush. Should the coat resist this treatment, brush with Spanish white, then wash, dry, and pass through alcohol. The employment of Spanish white has the drawback of shining the silver if the application is strong and prolonged. If the oxidation has withstood these means and if it is desired to impart to the chain the handsome mat appearance of new goods, it should be annealed in charcoal dust and passed through vitriol, but this operation, for those unused to it, is very dangerous to the soldering and consequently may spoil the piece.

«Coloring Silver.»—A rich gold tint may be imparted to silver articles by plunging them into dilute sulphuric acid, saturated with iron rust.

«Frosting Polished Silver.»—Articles of polished silver may be frosted by putting them into a bath of nitric acid diluted with an equal volume of distilled water and letting them remain a few minutes. A better effect may be given by dipping the article frequently into the bath until the requisite degree of frosting has been attained. Then rinse and place for a few moments in a strong bath of potassium cyanide; remove and rinse. The fingers must not be allowed to touch the article during either process. It should be held with wooden forceps or clamps.

«Fulminating Silver.»—Dissolve 1 part of fine silver in 10 parts of nitric acid of 1.36 specific gravity at a moderate heat; pour the solution into 20 parts of spirit of wine (85 to 90 per cent) and heat the liquid. As soon as the mixture begins to boil, it is removed from the fire and left alone until cooled off. The fulminic silver crystallizes on cooling in very fine needles of dazzling whiteness, which are edulcorated with water and dried carefully in the air.

«Hollow Silverware.»—A good process for making hollow figures consists in covering models of the figures, made of a base or easily soluble metal, with a thin and uniform coating of a nobler metal, by means of the electric current in such a way that this coating takes approximately the shape of the model, the latter being then removed by dissolving it with acid. The model is cast from zinc in one or more pieces, a well-chased brass mold being used for this purpose, and the separate parts are then soldered together with an easily fusible solder. The figure is then covered with a galvanized coating of silver, copper, or other metal. Before receiving the coating of silver, the figure is first covered with a thin deposit of copper, the silver being added afterwards in the required thickness. But in order {641} that the deposit of silver may be of the same thickness throughout (this is essential if the figure is to keep the right shape), silver anodes, so constructed and arranged as to correspond as closely as possible to the outlines of the figure, should be suspended in the solution of silver and cyanide of potassium on both sides of the figure, and at equal distances from it. As soon as the deposit is sufficiently thick, the figure is removed from the bath, washed, and put into a bath of dilute sulphuric or hydrochloric acid, where it is allowed to remain till the zinc core is dissolved. The decomposition of the zinc can be accelerated by adding a pin of copper. The figure now requires only boiling in soda and potassic tartrate to acquire a white color. If the figure is to be made of copper, the zinc model must be covered first with a thin layer of silver, then with the copper coating, and then once more with a thin layer of silver, so that while the zinc is being dissolved, the copper may be protected on either side by the silver. Similar precautions must be taken with other metals, regard being paid to their peculiar properties. Another method is to cast the figures, entire or in separate parts, out of some easily fusible alloy in chased metal molds. The separate portions are soldered with the same solder, and the figure is then provided with a coating of copper, silver, etc., by means of the galvanic current. It is then placed in boiling water or steam, and the inner alloys melted by the introduction of the water or steam through holes bored for this purpose.

«Lustrous Oxide on Silver» (see also Plating and Silver, under Polishes).—Some experience is necessary to reproduce a handsome black luster. Into a cup filled with water throw a little liver of sulphur and mix well. Scratch the silver article as bright as possible with the scratch brush and dip into the warm liquid. Remove the object after 2 minutes and rinse off in water. Then scratch it up again and return it into the liquid. The process should be repeated 2 or 3 times, whereby a wonderful glossy black is obtained.

«Ornamental Designs on Silver.»—Select a smooth part of the silver, and sketch on it a monogram or any other design with a sharp lead pencil. Place the article in a gold solution, with the battery in good working order, and in a short time all the parts not sketched with the lead pencil will be covered with a coat of gold. After cleaning the article the black lead is easily removed with the finger, whereupon the silver ornament is disclosed. A gold ornament may be produced by reversing the process.

«Separating Silver from Platinum Waste.»—Cut the waste into small pieces, make red hot to destroy grease and organic substances, and dissolve in aqua regia (hydrochloric acid, 3 parts, and nitric acid, 1 part). Platinum and all other metals combined with it are thus dissolved, while silver settles on the bottom as chloride in the shape of a gray, spongy powder. The solution is then drawn off and tested by oxalic acid for gold, which is precipitated as a fine yellowish powder. The other metals remain untouched thereby. The platinum still present in the solution is now obtained by a gradual addition of sal ammoniac as a yellowish-gray powder. These different precipitates are washed with warm water, dried, and transformed into the metallic state by suitable fluxes. Platinum filings, however, have to be previously refined. They are also first annealed. All steel or iron filings are removed with a magnet and the rest is dipped into concentrated sulphuric acid and heated with this to the boiling point. This process is continued as long as an action of the acid is noticeable. The remaining powder is pure platinum. Hot sulphuric acid dissolves silver without touching the platinum. The liquid used for the separation of the platinum is now diluted with an equal quantity of water and the silver expelled from it by means of a saturated cooking salt solution. The latter is added gradually until no more action, i. e., separation, is perceptible. The liquid is carefully drawn off, the residue washed in warm water, dried and melted with a little soda ashes as flux, which yields pure metallic silver.

The old process for separating silver from waste was as follows: The refuse was mixed with an equal quantity of charcoal, placed in a crucible, and subjected to a bright-red heat, and in a short time a silver button formed at the bottom. Carbonate of soda is another good flux.

«Silvering Glass Globes.»—Take 1⁠/⁠3 ounce of clean lead, and melt it with an equal weight of pure tin; then immediately add 1⁠/⁠2 ounce of bismuth, and carefully skim off the dross; remove the alloy from the fire and before it grows cold add 5 ounces of mercury, and stir the whole well together; then put the fluid amalgam into a clean glass, and it is fit for use. When this amalgam is used for silvering {642} let it be first strained through a linen rag; then gently pour some ounces thereof into the globe intended to be silvered; the alloy should be poured into the globe by means of a paper or glass funnel reaching almost to the bottom of the globe, to prevent it splashing the sides; the globe should be turned every way very slowly, to fasten the silvering.

«Silvering Powder for Metals.»—Copper, brass, and some other metals may be silvered by rubbing well with the following powder: Potassium cyanide, 12 parts; silver nitrate, 6 parts; calcium carbonate, 30 parts. Mix and keep in a well-closed bottle. It must be applied with hard rubbing, the bright surface being afterwards rinsed with water, dried, and polished. Great care must be exercised in the use of the powder on account of its poisonous nature. It should not be allowed to come in contact with the hands.

«Silver Testing.»—For this purpose a cold saturated solution of potassium bichromate in pure nitric acid of 1.2 specific gravity is employed. After the article to be tested has been treated with spirit of wine for the removal of any varnish coating which might be present, a drop of the above test liquor is applied by means of a glass rod and the resultant spot rubbed off with a little water.

A testing solution of potassium bichromate, 1 ounce, pure nitric acid, 6 ounces, and water, 2 ounces, gives the following results on surfaces of the metals named:

───────────────+──────────────────+──────────────── Metal. │ Color in one │ Color of mark │ minute. │ left. ───────────────+──────────────────+──────────────── Pure silver │ Bright blood-red │ Grayish white .925 silver │ Dark red │ Dark brown .800 silver │ Chocolate │ Dark brown .500 silver │ Green │ Dark brown German silver │ Dark blue │ Light gray Nickel │ Turquoise blue │ Scarcely any Copper │ Very dark blue │ Cleaned copper Brass │ Dark brown │ Light brown Lead │ Nut brown │ Leaden Tin │ Reddish brown │ Dark Zinc │ Light chocolate │ Steel gray Aluminum │ Yellow │ No stain Platinum │ Vandyke brown │ No stain Iron │ Various │ Black 9-carat gold │ Unchanged │ No stain ───────────────+──────────────────+────────────────

The second column in the table shows such change of color as the liquid—not the metal—undergoes during its action for the period of 1 minute. The test liquid being then washed off with cold water, the third column shows the nature of the stain that is left.

In the case of faintly silvered goods, such as buttons, this test fails, since the slight quantity of resulting silver chromate does not become visible or dissolves in the nitric acid present. But even such a thin coat of silver can be recognized with the above test liquor, if the bichromate solution is used, diluted with the equal volume of water, or if a small drop of water is first put on the article and afterwards a little drop of the undiluted solution is applied by means of a capillary tube. In this manner a distinct red spot was obtained in the case of very slight silvering.

A simpler method is as follows: Rub the piece to be tested on the touchstone and moisten the mark with nitric acid, whereupon it disappears. Add a little hydrochloric acid with a glass rod. If a white turbidness (silver chloride) appears which does not vanish upon addition of water, or, in case of faint silvering or an alloy poor in silver, a weak opalescence, the presence of silver is certain. Even alloys containing very little silver give this reaction quite distinctly.

«Pink Color on Silver.»—To produce a beautiful pink color upon silver, dip the clean article for a few seconds into a hot and strong solution of cupric chloride, swill it in water and then dry it or dip it into spirit of wine and ignite the spirit.

SILVER, IMITATION: See Alloys.

SILVERING: See Plating.

SILVERING OF MIRRORS: See Mirrors.

SILVERING, TEST FOR: See Plating.

SILVER FOIL SUBSTITUTE: See Metal Foil.

SILVER NITRATE SPOTS, TO REMOVE: See Cleaning Preparations and Methods.