Bronze.—(a) For cleaning bronze statues, when blackened by smoke and soot, wash with plenty of clean water, accompanied with mechanical friction. Even this simple treatment is undesirable; because the friction, however slight, accompanying the washing, destroys, or tends to destroy, the sharpness of the outlines; and the sulphurous and sulphuric acids of the prevailing smoke rapidly corrode the surface of any bronze statue which is constantly being washed. For these reasons, the Nelson monument at Liverpool, was left untouched when it was re-erected, after the building of the new Exchange surrounding it. It has been a matter of much debate whether the soot-blackened surface of a bronze statue is not more pleasing to the eye, than the metallic lustre of a new, or newly-cleaned statue. (b) Weber finds that a dilute solution of caustic alkalies removes overlying dirt, and allows the green patina to become visible. Where the metal was not originally oxidised, the alkali simply cleanses it, and does not promote any formation of green rust. (c) By dipping fustian in soluble glass, and washing it with soap directly afterwards, we get a fabric largely impregnated with silica, which will be found very well adapted for cleaning bronzes, &c. Samples of the material were in the Vienna Exhibition, and attracted some notice. (d) The method of restoring a bronze tea-urn turned black in parts will depend, to a great extent, on the metal and the colour. Clean the surface, first of all, with whiting and water, or crocus powder, until it is polished; then cover with a paste of graphite and crocus, mixed in the proportions that will produce the desired colour. Heat the paste over a small charcoal fire. If the bronzing has been produced by a corrosive process, try painting a solution of potassium sulphide over the cleaned metal. There are many recipes for bronzing, and it is impossible to say which is suitable. The bronzed surface may be polished; but it cannot be bright unless the surface of the metal itself is polished, and then covered with transparent lacquer to preserve the brightness.
Coins.—Coins can be quickly cleansed by immersion in strong nitric acid, and immediate washing in water. If very dirty, or corroded with verdigris, it is better to give them a rubbing with ½ oz. pure potash bichromate, 1 oz. sulphuric acid, 1 oz. nitric acid; rub over, wash with water, wipe dry, and polish with rottenstone or chalk. (Lyle.)
Copper Electros.—Copper electros should be well cleaned after working, as the ink between the fine lines in time generates acids, which destroy the electro. For this purpose turpentine and the brush are employed; others also recommend the electros to be afterwards well rubbed with an oil as free from acid as possible. Should the ink be so dried up as to resist it, creosote should be applied, and the electros treated with the brush.
Copper Vessels.—Use soft-soap and rottenstone, made into a stiff paste with water, and dissolved by gently simmering in a water-bath. Rub on with a woollen rag, and polish with dry whiting and rottenstone. Finish with a leather and dry whiting. See also Brass.
Gas Chandeliers.—Very few chandeliers are gilt; they are burnished and lacquered with yellow lacquer. Proceed as follows, whether gilt or lacquered: Take the chandelier to pieces, and boil in strong soda lye for a few minutes; brush over with a soft brush, pass through a strong solution of potassium cyanide (deadly poison), wash through a tubful of boiling water, dry in clean sawdust, wipe up bright with a washleather, and relacquer.
Gilt Mountings.—Gilt mountings, unless carefully cleaned, soon lose their lustre. They should not be rubbed; if slightly tarnished, wipe them off with a piece of Canton flannel, or what is better, remove them if possible, and wash in a solution of ½ oz. borax dissolved in 1 lb. water, and dry them with a soft linen rag; their lustre may be improved by heating them a little, and rubbing with a piece of Canton flannel.
Gold.—(a) To remove the brown tarnish from coloured gold, take a piece of tissue-paper damped in liq. ammoniæ, gently rub the gold till the tarnish disappears, then wash off carefully with soft brush, soap, and water, dry in sawdust or before the fire; if this is not sufficient, entrust the article to a jeweller. (b) Mix a little rouge and spirits of wine together, and apply to the jewellery with a rather stiff brush, and turn the brush round and round—not to brush as if to polish, but rather tickle it and pat it with the hair of the brush; but be sure to keep the brush wet with the mixture. After you have got the tarnish off, wash it out with soap and boiling water, and dry in box-dust. Take care of any stones with foil behind. (c) Rub with a piece of tissue-paper, screwed up and wet with the tongue. This will often do it; if not, re-colour it. (d) A weak solution of potassium cyanide will clean gold braid. Use with small sponge, and wash off with clean water. Strength, say 10 or 15 gr. to the oz. of water. Care should be taken that the solution does not get into any cuts or wounds, as it is very poisonous. The strength of the solution would greatly depend on the condition of the lace. It can be made stronger if necessary. (e) A solution of 20 dr. lime chloride, 20 dr. soda bicarbonate, and 5 dr. common salt, in 5¼ pints distilled water, is prepared and kept in well-closed bottles. The article to be cleaned is allowed to remain a short time in this solution (which is to be heated only in the case of very obstinate dirt), then taken out, washed with spirit, and dried in sawdust. (Chem. Cent. Blatt.)
Iron and steel.—(a) Take a spongy piece of fig-tree wood and well saturate it with a mixture of sweet-oil and finely powdered emery, and with this well rub all the rusty parts. This will not only clean the article, but will at the same time polish it, and so render the use of whiting unnecessary. (b) Bright iron or steel goods (as polished grates and fire-irons) may be preserved from rust in the following manner. Having first been thoroughly cleaned, they should be dusted over with powdered quicklime, and thus left until wanted for use. Coils of piano-wire are covered in this manner, and will keep free from rust for many years. (c) Dissolve ½ oz. camphor in 1 lb. hogs’ lard, and take off the scum; then mix with the lard as much black-lead as will give the mixture an iron colour. Rub the articles all over with this mixture, and let them lie for 24 hours; then dry with a linen cloth, and they will keep clean for months. (d) Table knives which are not in constant use should be put in a case containing a depth of about 8 in. quicklime. They are to be plunged into this to the top of the blades, but the lime must not touch the handles. (e) Steel bits that are tarnished, but not rusty, can be cleaned with rottenstone, common hard soap, and a woollen cloth. (f) Removing paint from iron.—After a number of experiments, it has been found that a paint-softener made of 1 lb. lime to 4 lb. potash and 6 qt. water works better than any other proportions.
Plate Powders.—(a) Equal parts precipitated iron subcarbonate, and prepared chalk. (b) An impalpable rouge may be prepared by calcining iron oxalate. (c) Take quicksilver with chalk, ½ oz., and prepared chalk 2 oz., mix them. When used, add a small quantity of spirits of wine, and rub with chamois leather. (d) Put iron sulphate into a large tobacco pipe, and place it in a fire for ¼ hour, mix with a small quantity of powdered chalk. This powder should be used dry. (e) The following makes a liquid polish for silver plate—3 to 4 dr. potassium cyanide, 8 to 10 gr. silver nitrate, and 4 oz. water; apply with a soft brush, wash the object thoroughly with water, dry with a soft linen cloth, and polish with a chamois skin. (f) Take 2 oz. hartshorn powder and boil it in 1 pint water; soak small squares of damask cloth in the liquid, hang them up to dry, and they will be ready for use, and better than any powders. (g) Add by degrees 8 oz. prepared chalk in fine powder to a mixture of 2 oz. spirits of turpentine, 1 oz. alcohol, ½ oz. spirits of camphor, and 2 dr. aqua ammonia; apply with a sponge, and allow it to dry before polishing. (h) Mix together 1 oz. fine chalk, 2 oz. cream of tartar, 1 oz. rottenstone, 1 oz. red-lead, and ¾ oz. alum; pulverise thoroughly in a mortar. Wet the mixture, rub it on the silver, and, when dry, rub off with a dry flannel, or clean with a small brush. (i) An excellent preparation for polishing plate may be made in the following manner:—Mix together 4 oz. spirits of turpentine, 2 oz. spirits of wine, 1 oz. spirits of camphor, and ½ oz. spirits of ammonia. To this add 1 lb. whiting, finely powdered, and stir till the whole is of the consistency of thick cream. Use this preparation with a clean sponge, cover the silver with it, so as to give it a coat like whitewash. Set the silver aside till the paste has dried into a powder; then brush off, and polish with a chamois leather. A cheaper kind may be made by merely mixing spirits of wine and whiting together.
Silver and Plated Goods.—(a) East Indian jewellers never touch silver ware with any abrasive substance, but use, instead of polishing paste, &c., slices of lemons; the goods to be cleaned are well rubbed with these, and then left in a pan for a few hours, covered with slices. For delicate jewellery, a large lime is cut in half, the article inserted, the two halves applied together and tied up for some hours; the article is then washed in several waters, placed in a pan of nearly boiling soapsuds, stirred about, rinsed, and dried on a metal plate, the smooth parts being gently rubbed with wash-leather, if required. (b) Potassium cyanide solution (rather weak) dissolves off the dirty surface gradually, but great care is required. (c) Green tamarind pods (potash oxalic) are greater detergents for gold and silver than lemons, and are often employed for the purpose of removing stains, firemarks, &c. (Boston Journal of Chemistry.) (d) Eisner states that a polish equal to that obtained by the use of the finest plate powder, can be produced by simply cleaning the silver in water in which potatoes have been boiled. (e) Dead or engraved silver goods should never be cleaned with plate powder, but be washed out with a soft brush and some strong alkali, and well rinsed afterwards. When the dead or frosted parts are quite dry, the polished parts are carefully cleaned with powder. (f) The following directions are given by a silversmith in Christiania:—Silver filagree work is best cleaned by the application of spirit of ammonia by means of a soft brush, and afterwards thoroughly washing in soft-soap and warm water, and rinsing in clean warm water, and quick drying by linen rags, blotting-paper, or some similar clean absorbent. Should this method, after several repetitions, cease to have the required effect, the article will have to be sent to a silversmith to be heated and boiled in acid. The best mode of preservation is to wrap the article in tissue paper before placing it in the case. (g) The simplest and cleanest substance for cleaning silver articles is, according to Professor Davenport, soda hyposulphite. It acts quickly, and is inexpensive. A rag or a brush, moistened with a saturated solution of the salt, cleanses even strongly oxidised silver surfaces in a few seconds, without the application of any polishing powder. (h) Mix 8 oz. prepared chalk, 2 oz. turpentine, 1 oz. alcohol, 4 dr. spirits of camphor, and 2 dr. liquor of ammonia. Apply this mixture to the article with a sponge, and allow to dry before polishing. (i) Dissolve 12 oz. potassium cyanide in 1 qt. water; dip in this solution, and brush it with a stiff brush until clean; then wash and dry. (j) A paste composed of washed whiting, precipitated magnesia carbonate, and precipitated iron peroxide. (k) Gin. (l) Apply whiting mixed with sweet oil on a shammy. (m) Take 2 qt. water, ½ oz. hartshorn, and 1 oz. whiting, and boil the whole together. While boiling, put as many of the silver or plated articles into the vessel as it will conveniently hold, and let remain for 5 minutes; withdraw, and leave to dry. Polish with clean linen or woollen rags, which, after being soaked in the above-named liquor, have been well wrung. Finally rub with a clean soft leather. (n) The ink eraser sold by stationers has the property of cleaning and brightening silver and gold mountings, such as meerschaum pipe fittings, pencil-cases, watch-cases, &c. (o) Cut some flakes of white curd soap, and put them into a saucepan of water to simmer; sew the ornaments up in a muslin bag, and place in the liquid for about 10 minutes whilst on the fire.