BRONZE POWDERS 539 



BRONZB PAXHTT. Bronzo paint, commonly called gold paint, is mado by 

 mixing gold-coloured bronze powder with pure turpentine as a vehicle. The tur- 

 pentine of commerce has at all times an acid reaction, which is detrimental to the 

 colour of the metal powder. The tarpentino used for this purpose has, therefore, to 

 bo mixed with lime to neutralise the acid before it is thus employed. 



BRONZE POWDERS have been much used of late in the decorative painting of 

 houses, &c. They are prepared of every shade, from that of bright gold to orange, 

 dark copper, emerald green, &c. Pale gold is produced from an alloy of 13 of 

 copper and 2J of zinc ; crimson metallic lustre from copper : ditto, paler, copper 

 and a very little zinc; green bronze with a proportion of verdigris; another fine 

 orange by 14'4 copper and if zinc; another ditto, 13| copper and 2'4zinc: a beautiful 

 pale gold from an alloy of the two metals in atomic proportions. 



The alloy is laminated into very fine leaves with careful annealing, and these are 

 levigated into impalpable powders along with a film of fine oil to prevent oxidisemont, 

 and to favour the levigation. 



Mr. Brandeis, in his account of his articles of manufacture furnished to the New 

 York Exhibition, says : 



' Bronzes, or, more correctly, metallic powders resembling gold dust, were invented 

 in 1648, by a monk, at Furth, in Bavaria, named Theophrastus Allis Bombergensis. 

 He took the scraps or cuttings of the metallic leaves then known as ' Dutch leaf,' 

 and ground them with honey. This roughly made bronze powder was used for 

 ornamenting parchments, capital letters in Bibles, choral books, &c.' 



At Furth bronze powders are largely made for Europe, and with little change or 

 improvement. There are four sorts of Dutch leaf : 



Common leaf, soft, and of reddish cast, composed of 25 or 30 per cent, of zinc to 

 75 or 70 per cent, of copper. 



French leaf contains more zinc, is harder, less ductile, and has a purer yellow colour* 



Florence leaf has a larger proportion of zinc, and is of a greenish gold colour ; 

 and lastly, 



White leaf, composed of tin. The more zinc these alloys contain, the harder, the 

 more brittle, and more difficult are they to work into perfect leaves. The manner of 

 beating is similar to the mode for producing gold leaves. 



The scraps, cuttings, and fragments of these leaves are the materials for the German 

 bronze powders. First brushed through a sieve and ground with gum water on 

 marble slabs for six hours, the gum washed out, the powders sorted, dried, and a 

 coating of grease given to make them appear more brilliant, and to protect them from 

 oxidation. Varieties of colour, such as orange, &c., are produced by a film of sub- 

 oxide upon the surface of the particles. The price of bronze powders depends upon 

 the demand, and the supply of the waste material of the metal leaves, and prices 

 change accordingly. 



Messrs. Brandeis patent their process, and in place of being dependent upon 

 uncertain supplies of metal of unknown composition, they take the metals at once in 

 a state of purity (say copper by voltaic precipitation) : it is alloyed with zinc, cast into 

 ingots, rolled into ribands, cut, annealed, and rolled until the metal is thin and leaf- 

 like ; then it is taken to a steam-mill, and ground. The bronze powder is washed 

 out and dried, then introduced into an air-tight room, with an arrangement of boxes ; 

 the air of the chamber is set in violent motion by bellows, and the powder diffused 

 throughout ; the bronze powders are deposited, the finest in the upper boxes, and 

 the coarser powders below. When settled, mineral varnish is introduced ; the boxes 

 fitted with tight lids are made to revolve, and the particles are thus rapidly coated, 

 and the highest metallic brilliancy imparted. Different shades of colour, pink, crim- 

 son, &c., are produced by submitting the powder to heat and oxidation before the 

 rapid revolutions of the varnishing boxes. 



The quantity thus produced by one firm, with three steam-engines at work, enables 

 the finished bronze powders to be produced at a rate about equal to the price the 

 German manufacturer has to pay for his materials the cuttings and scraps of leaves. 

 Hence, for the purposes of trade and art, a largo exportation of bronze powders 

 takes place from America to Europe, South America, and China. 



The bronze powders are largely used in japanning, bronzing tin and iron goods, 

 ornamental works of paper, wood, oil-cloth, leather, &c. ; -while sign-boards and the 

 decoration of public buildings have effective metallic brilliant surfaces of beauty and 

 durability. In fact, for ornamental decorations, the demand steadily increases. 



In Holland and Germany the subject has been examined, with the view of ascer- 

 taining the effect of chemical composition. 



Do Heer E. K. Konig has given a Table of the analyses of the best European 

 samples of bronze powders and leaves ( Volksfiighf) : 



