(1) Wash with rock alum, boiled in a strong lye in the proportion of 1 oz. to a pint; polish with dry tripoli. (2) The government method prescribed for cleaning brass, and in use at all the United States arsenals, is claimed to be the best in the world. The plan is to make a mixture of 1 part cdmmon nitric acid and 1/2 part sulphuric acid, in a stone jar,, having also ready a pail of fresh water and a box of sawdust. The articles to be treated are dipped into the acid, then removed into the water, and finally rubbed with sawdust. This immediately changes them to a brilliant colour. If the brass has become greasy, it is first dipped in a strong solution of potash and soda in warm water; this cuts the grease, so that the acid has free power to act. (3) Rub the surface of the metal with rottenstone and sweet oil, then rub off with a piece of cotton flannel, and polish with soft leather. A solution of oxalic acid rubbed over tarnished brass soon removes the tarnish, rendering the metal bright. The acid must be washed off with water, and the brass rubbed with whiting and soft leather.
A mixture of muriatic acid and alum dissolved in water imparts a golden colour to brass articles that are steeped in it for a few seconds. (4) First boil your articles in a pan with ordinary washing soda, to remove the old lacquer; then let them stand for a short time in dead aquafortis; then run them through bright dipping ditto. Swill all acid off in clean water, and brighten the relieved parts with a steel burnisher, replace in clean water, and dry out in beech sawdust. Next place your work on stove till heated, so that you can with difficulty bear your hand on articles, and apply pale lacquer with brush: the work will burn if heated too much or too rapidly. (5) Put a coat of nitric acid over the part you want cleaned, with a piece of rag; as soon as it turns a light yellow, rub it dry and the brass will present a very clean appearance; if not, repeat. (6) Oxalic acid and whiting mixed and applied wet, with brush, and brushed again when dry with soft plate-brush to polish with dry whiting. (7) Brass instruments. If the instruments are very much oxidized or covered with green rust, first wash them with strong soda and water. If not so very bad, this first process may be dispensed with.
Then apply a mixture of 1 part common sulphuric acid and 12 of water, mixed In an earthen vessel, and afterwards polish with oil and rottenstone, well scouring with oil and rottenstone, and using a piece of soft leather and a little dry rottenstone to give a brilliant polish. In future cleaning, oil and rottenstone will be found sufficient. (8) Take a strip of coarse linen, saturate with oil and powdered rottenstone, put round the tubing of instrument, and work backwards and forwards; polish with dry rottenstone. Do not use acid of any kind, as it is injurious to the joints. To hold the instrument, get a piece of wood turned to insert in the bells; fix in a bench vice. The piece of wood will also serve for taking out any dents you may get in the bells. (9) Oil and rottenstone for this purpose, are, though very efficacious, objectionable on account of dirt, on account of the oil finding its way to the pistons, and because the instrument cleaned in this manner so soon tarnishes. Dissolve some common soda in warm water, shred into it some scraps of yellow soap, and boil it till the soap is all melted. Then take it from the fire, and when it is cool add a little turpentine, and sufficient rottenstone to make a stiff paste.
Keep it in a tin box covered from the air, and if it get hard, moisten a small quantity with water for use. (10) Brass or Copper. - Mix together 1 oz. oxalic acid, 6 oz. rcttenstone, and 1/2 oz. gum arabic; all these are to be finely powdered. Then add 1 oz. sweet oil and sufficient wate/ to form the mixture into a paste. Apply a small portion to the article to be cleaned, and rub dry with a flannel or washleather. Bronze. - (l) There has been found no other way of cleaning bronze statues, when blackened by smoke and soot, than that of washing with plenty of clean water, accompanied with mechanical friction; and it has been generally allowed, in the numerous discussions which have occurred on the subject, that even this simple treatment was very 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 would be certain to rapidly corrode the surface of any bronze statue which is constantly being washed. For these reasous, 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. (2) 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 oxidized, the alkali simply cleanses it, and does not promote any formation of green rust. (3) 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 veiy well adapted for cleaning bronzes, etc. Samples of the material were in the Vienna Exhibition, and attracted some notice. (4) The method of restoring a bronze tea-urn turned black in parts will depend, to a great extent, oh 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 sulphuret of potassium 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.