Part 378

«Platinizing Copper and Brass.»—I.—The articles are coated with a thin layer of platinum in a boiling solution of platinum sal ammoniac, 1 part; sal ammoniac, 8 parts; and water, 40 parts, and next polished with chalk. A mixture of equal parts of platinum sal ammoniac and tartar may also be rubbed on the objects. Steel and iron articles can be platinized with an ethereal solution of platinic chloride. For small jewelry the boiling solution of platinic chloride, 10 parts; cooking salt, 200 parts; and water, 1,000 parts, is employed, which is rendered alkaline with soda lye. In this, one may also work with zinc contact.

II.—Heat 800 parts of sal ammoniac and 10 parts of platinum sal ammoniac to the boiling point with 400 parts of water, in a porcelain dish, and place the articles to be platinized into this, whereby they soon become covered with a coating of platinum. They are then removed from the liquid, dried and polished with whiting.

«Platinizing on Glass or Porcelain.»—First dissolve the platinum at a moderate temperature in aqua regia, and next evaporate the solution to dryness, observing the following rules: When the solution commences to turn thick it is necessary to diminish the fire, while carrying the evaporation so far that the salt becomes dry, but the solution should not be allowed to acquire a brown color, which occurs if the heat is too strong. The result of this first operation is chloride of platina. When the latter has cooled off it should be dissolved in alcohol (95 per cent). The dissolution accomplished, which takes place at the end of 1 or 2 hours, throw the solution gradually into four times its weight of essence of lavender, then put into a well-closed flask.

For use, dip a brush into the solution and apply it upon the objects to be platinized, let dry and place in the muffle, leaving them in the oven for about one-half hour. In this operation one should be guided as regards the duration of the baking by the hardness or fusibility of the objects treated. The platinization accomplished, take a cotton cloth, dipped into whiting in the state of pulp, and rub the platinated articles with this, rinsing with water afterwards.

«Platinizing Metals.»—Following are several processes of platinizing on metals:

It is understood that the metals to be covered with platinum must be copper or coppered. All these baths require strong batteries.

I.—Take borate of potash, 300 parts, by weight; chloride of platina, 12 parts; distilled water, 1,000 parts.

II.—Carbonate of soda, 250 parts, by weight; chloride of platina, 10 parts; distilled water, 1,000 parts.

III.—Sulphocyanide of potash, 12 parts, by weight; chloride of platina, 12 parts; carbonate of soda, 12 parts; distilled water, 1,000 parts.

IV.—Borate of soda, 500 parts, by weight; chloride of platina, 12 parts; distilled water, 1,000 parts. {587}

«SILVERING, SILVER-PLATING, AND DESILVERING:»

See also Silvering by Oxidation, under Oxidation Processes, under Plating.

«Antique Silver.»—There are various processes for producing antique silver, either fat or oxidized:

To a little copal varnish add some finely powdered ivory black or graphite. Thin with spirits of turpentine and rub with a brush dipped into this varnish the objects to be treated. Allow to dry for an hour and wipe off the top of the articles with some rag, so that the black remains only in the hollows. If a softer tint is desired, apply again with a dry brush and wipe as the first time. The coating of black will be weaker and the shade handsomer.

«Britannia Silver-Plating.»—I.—The article should first be cleaned and then rubbed by means of a wet cloth with a pinch of powder obtained by mixing together: Nitrate of silver, 1 part; cyanide of potassium, 2 parts; chalk, 5 parts. Then wipe with a dry cloth, and polish well with rouge to give brilliancy.

II.—By the electric method the metal is simply plunged into a hot saturated solution of crude potassium carbonate, and the plating is then done directly, using a strong electrical current. The potassium carbonate solution dissolves the surface of the britannia metal and thus enables the silver to take a strong hold on the article.

«To Silver Brass, Bronze, Copper, etc.»—I.—In order to silver copper, brass, bronze, or coppered metallic articles, dissolve 10 parts of lunar caustic in 500 parts of distilled water, and 35 parts of potassium cyanide (98 per cent) in 500 parts of distilled water; mix both solutions with stirring, heat to 176° to 194° F. in an enameled vessel, and enter the articles, well cleansed of fat and impurities, until a uniform coating has formed.

II.—Zinc, brass, and copper are silvered by applying a paste of the following composition: Ten parts of silver nitrate dissolved in 50 parts of distilled water, and 25 parts of potassium cyanide dissolved in distilled water; mix, stir, and filter. Moisten 100 parts of whiting and 400 parts of powdered tartar with enough of the above solution to make a paste-like mass, which is applied by means of a brush on the well-cleaned objects. After the drying of this coating, rinse off, and dry in sawdust.

III.—To silver brass and copper by friction, rub on the articles, previously cleaned of grease, a paste of silver chloride, 10 parts; cooking salt, 20 parts; powdered tartar, 20 parts; and the necessary water, using a rag.

«Desilvering.»—I.—It often happens in plating that, notwithstanding all precautions, some pieces have failed and it is necessary to commence the work again. For removing the silver that has been applied, a rapid method is to take sulphuric acid, 100 parts, and nitrate of potash, 10 parts. Put the sulphuric acid and the nitrate of potash (saltpeter) in a vessel of stoneware or porcelain, heated on the water bath. When the silver has been removed from the copper, rinse the object several times and recommence the silvering. This bath may be used repeatedly, taking care each time to put it in a stoppered bottle. When it has been saturated with silver and has no more strength, decant the deposit, boil the liquor to dryness, add the residue to the deposit, and melt in a crucible to regenerate the metal.

II.—To dissolve the silver covering of a metallic object, a bath is made use of, composed of 66 per cent sulphuric acid, 3 parts, and 40 per cent nitric acid, 1 part. This mixture is heated to about 176° F., and the objects to be desilvered are suspended in it by means of a copper wire. The operation is accomplished in a few seconds. The objects are washed and then dried in sawdust.

«To Silver Glass Balls and Plate Glass.»—The following is a method for silvering the glass balls which are used as ornaments in gardens, glass panes, and concave mirrors: Dissolve 300 parts of nitrate of silver and 200 parts of ammonia in 1,300 parts of distilled water. Add 35 parts of tartaric acid dissolved in 4 times its weight of water. Dilute the whole with 15,000 to 17,000 parts of distilled water. Prepare a second solution containing twice the amount of tartaric acid as the preceding one. Apply each of these solutions successively for 15 to 20 minutes on the glass to be silvered, which must previously have been cleaned and dried. When the silvering is sufficient, wash the object with hot water, let dry, and cover with a brown varnish.

«Iron Silver-Plating.»—I.—Iron articles are plated with quicksilver in a solution of nitrate of mercury before being silvered. The quicksilver is then removed by heating to 572° F. The articles may also be first tinned to economize the silver. Steel is dipped in a mixture of {588} nitrate of silver and mercury, each dissolved separately in the proportion of 5 parts, by weight, to 300 parts, by weight, of water, then wiped to remove the black film of carbon, and silvered till a sample dipped in a solution of blue vitriol ceases to turn red. According to H. Krupp, articles made of an alloy of nickel, copper, and zinc, such as knives, forks, spoons, etc., should be coated electrically with nickel, put into a solution of copper like that used for galvanic coppering, and then electroplated.

II.—A brilliant silver color may be imparted to iron (from which all grease has been previously removed) by treating it with the following solution: Forty parts, by weight, chloride of antimony; 10 parts, by weight, powdered arsenious acid; and 80 parts levigated hematite are mixed with 1,000 parts of 90 per cent alcohol and gently heated for half an hour on a water bath. A partial solution takes place, and a small cotton pad is then dipped in the liquid and applied with a gentle pressure to the iron. A thin film consisting of arsenic and antimony is precipitated, as described by Dr. Langbein, in his “Handbuch der galv. Metallniederschläge.” The brilliancy of the effect depends upon the care with which the iron has previously been polished.

«To Silver-Plate Metals.»—I.—Nitrate of silver, 30 parts, by weight; caustic potash, 30 parts; distilled water, 100 parts. Put the nitrate of silver into the water; one-quarter hour afterwards add the potash, and, when the solution is done, filter. It is sufficient to dip the objects to be silvered into this bath, moving them about in it for 1 or 2 minutes at most; then rinsing and drying in sawdust. It is necessary to pickle the pieces before using the bath. To make the nitrate of silver one’s self, take 30 parts of pure silver and 60 parts of nitric acid, and when the metal is dissolved add the caustic potash and the water.

II.—Kayser’s silvering liquid, which is excellent for all kinds of metals, is prepared from lunar caustic, 11 parts; sodium hyposulphite, 20 parts; sal ammoniac, 12 parts; whiting, 20 parts; and distilled water, 200 parts. The articles must be cleaned well.

«Mosaic Silver.»—This compound consists of tin, 3 parts, by weight; bismuth, 3 parts; and mercury, 1 1⁠/⁠2 parts. The alloy of these metals is powdered finely, thus forming a silvery mass used for imitation silvering of metals, paper, wood, etc. In order to impart to metals, especially articles of copper and brass, an appearance similar to silver, they are made perfectly bright. The powder of the mosaic silver is mixed with six times the volume of bone ashes, adding enough water to cause a paste and rubbing this on the metallic surface by means of a cork of suitable shape. In order to silver paper by means of this preparation it is ground with white of egg, diluted mucilage, or varnish, and treated like a paint.

«Pastes for Silvering.»—I.—Carbonate of lime, 65 parts; sea salt, 60 parts; cream of tartar, 35 parts; nitrate of silver, 20 parts. Bray all in a mortar, not adding the carbonate of lime until the other substances are reduced to a fine powder. Next, add a little water to form a homogeneous paste, which is preserved in blue bottles away from the light. For use, put a little of this paste on a small pad and rub the article with it.