BRONZING 641 



When brass castings are to be bronzed, it is essential, in the first place, that they 

 should be thoroughly cleansed from grease, and brightened either -with the file or 

 emery-paper, or by boiling in a strong ley and then scouring with fine sand and 

 water. Vinegar alone is sometimes employed to produce the green bronze colour ; 

 sometimes dilute nitric acid, and often the muriate of ammonia (sal-ammoniac). This 

 latter salt and vinegar are frequently combined, and often a little common table salt 

 is added to the bronzing fluid. 



Coins and medals may be bronzed with the following solution : 2 parts of ver- 

 digris and 1 part of sal-ammoniac are to be dissolved in vinegar ; the solution is to be 

 boiled, skimmed, and diluted with water till it has only a weak metallic taste, and 

 upon further dilution lets fall no precipitate. This solution" is made to boil briskly, 

 and is poured upon the objects to be bronzed. These are well washed with clean 

 water, and then lacquered. 



To give fresh-made bronze objects an antique appearance, three quarters of an 

 ounce of sal-ammoniac, and a drachm and a half of binoxalate of potash (salt of 

 sorrel) are to be dissolved in a quart of vinegar, and a soft rag or brush moistened 

 with this solution is to be rubbed over the clean bright metal till its surface becomes 

 entirely dry by the friction. This process must be repeated several times to produce 

 the full effect ; and the object should be kept a little warm. Copper acquires very 

 readily a brown colour by rubbing it with a solution of the common liver of sulphur, 

 or sulphuret of potassium. 



The Chinese are said to bronze their copper vessels by taking 2 ounces of verdi- 

 gris, 2 ounces of cinnabar, 5 ounces of sal-ammoniac, and 5 ounces of alum, all in 

 powder, making them into a paste with vinegar, and spreading this pretty thick like a 

 pigment on the surfaces previously brightened. The piece is then to be held a little 

 while over a fire, till it becomes uniformly heated. It is next cooled, washed, and 

 dried ; after which it is treated in the same way once, and again till the wished-for 

 colour is obtained. An addition of sulphate of copper makes the colour incline more 

 to chestnut brown, and of borax more to yellow. It is obvious that the cinnabar 

 produces a thin coat of sulphuret of copper upon the surface of the vessel, and might 

 probably be used with advantage by itself. 



To give the appearance of antique bronze to modern articles, we should dissolve 1 

 part of sal-ammoniac, 3 parts of cream of tartar, and 6 parts of common salt in 

 1 2 parts of hot water, and mix with the solution 8 parts of a solution of nitrate 

 of copper of specific gravity T160. This compound, when applied repeatedly in a 

 moderately damp place to bronze, gives it in a short time a durable green coat, 

 which becomes by degrees very beautiful. More salt gives it a yellowish tinge, less 

 salt a bluish cast. A large addition of sal-ammoniac accelerates the operation of the 

 mordant. 



The best and most rapid bronzing liquid, which may be applied to copper, brass, 

 iron, or to new bronze, with equal advantage, is a solution of the chloride of platinum 

 (nitro-muriate of platinum), called chemical bronze ; but it is expensive. With the 

 chloride of platinum, almost any colour can be produced, according to the degree of 

 dilution and the number of applications. 



Some beautiful effects are produced upon bronze, and also upon iron castings, by 

 treating them with dilute acids. The action here is scarcely to be described as 

 bronzing ; it is, in fact, merely developing the true colour of the metal or alloy. 



With the view of rendering the action of the bronzing liquid as uniform as pos- 

 sible, small articles are dipped ; for larger articles, the bronzing liquid is dabbed 

 on plentifully with a linen rag. The dabbing process is to prevent the occurrence of 

 streaks, which might arise if the liquid were applied in straight strokes. When 

 properly bronzed and washed, the work is usually black-leaded, to give it a polished 

 appearance. 



Bronzing of Objects in Imitation of Metallic Bronze. Plaster of Paris, paper, 

 wood, and pasteboard, may be made to resemble pretty closely the appearance of 

 articles of real bronze, modern or antique. The simplest way of giving a brilliant 

 aspect of this kind is with a varnish made of the waste gold-leaf of the beater, ground 

 up on a porphyry slab with honey or gum- water. A coat of drying linseed-oil should 

 be first applied, and then the metallic powder is put on with a linen dossil. Mosaic 

 gold ground up with six parts of bone-ashes has been used in the same way. When 

 it is to be put on paper, it should be ground up alone with white of eggs or spirit 

 varnish, applied with a brush, and burnished when dry. When a plate of iron is 

 plunged into a hot solution of sulphate of copper, it throws down fine scales of copper, 

 which being repeatedly washed with water, and ground along with six times its weight 

 of bone-ashes, forms a tolerable brouziug. 



Browning of Gun-Barrels and other Arms. By this process the surface of several 

 articles of iron acquire a shining browu colour. This preparation, which protects the 



