On Polishing Metals. 243 



They finally proceed to the polishing, by employing the tri- 

 poli from Venice, which is most to be preferred, and is either 

 finely ground in water, or in olive-oil, according to the different 

 cases, for pieces of gold work, or the larger kinds of jewellery 

 articles, and until they perceive their surfaces are become per- 

 fectly brilliant ; they then finish them with tripoli, reduced to 

 an impalpable powder, and applied upon a very soft brush. 



For polishing those pieces of watch-work which are not to be 

 gilt ; after smoothening them with the grey or blue stone and 

 water, they polish them with rotten-stone well washed over, and 

 consequently vei*y fine, ground up with olive-oil, and finish 

 with dry rotten-stone. 



This rotten-stone is, according to M. Brongniart, a kind of 

 very light tripoli, but finer and more friable than the other 

 sorts. It comes from England, and is highly esteemed for po- 

 lishing with ; it is of an ashy-grey tint, and is found in thin 

 layers, upon the compact carbonate of lime, near Bakewell, in 

 Derbyshire. The polishing of steel is not executed in the same 

 manner as in polishing the softer metals ; the steel is not po- 

 lished until it has been hardened, and the harder it is the more 

 brilliant is its polish. 



The substances we have above indicated for polishing other 

 metals, are not powerful enough to attack a substance so hard 

 as this. We must employ emery, a substance so well known as 

 not to need describing here ; it is used after having been ground 

 in oil. 



The hardened steel is either polished flat, like glass, or cut in- 

 to facets, like a diamond, and, consequently, the lapidary's mill 

 is used. They commence by smoothening the work with emery, 

 rather coarse, then with finer emery, and finish with the finest. 

 The smoothening being perfected, they polish it with English 

 rouge, tritoxide of iron, and oil, and finally finish it with putty 

 of tin (peroxide of tin) and water ; but if upon mills, or laps of 

 zinc, then without the use of water. When the steel articles con- 

 sist of raised and hollow work, they are smoothened and polished 

 Avith the same substance ; but the instruments are, as in the 

 case of less harder metals, pieces of wood, properly shaped, and 

 employed in the same manner. 



GiJVs Repertory., Vol. vii. No. i. p. £7. 



