2s COATING OF IRON OR STEEl FOR15ES. 



would naturally occur, and not nmcli (if at all) acted upon by a 

 damp atmosphere, makes a fairly durable finish for such articles, 

 and resists natural changes in a generally satisfactory manner. 



Sometimes the artizan, wishing to produce this kind of surface 

 in an expeditious manner, upon an article of steel or iron, will 

 heat the article to a proper degree, and then smear upon it some 

 heavy oil or fat, after which he will continue the heating for a 

 while longer, and thus in a sort of impromptu manner obtain a 

 surface which will resist natural oxidation from exposure to the 

 weather, for a moderate length of time, fairly well. The exact 

 effect of this rough-and-ready process is, probably, that a very 

 thin film of superoxidation by heat is obtained, and, in addition 

 to that, a slight carbonization of the surface, by the burning 

 thereon of the greasy matter with wdiich it had been smeared, 

 and also a filling up of the minute surface-cells-of the metal, by 

 the same agent, which becomes hardened by the heat into a more 

 or less durable varnish. 



Contrasts in color between different parts (,)f instruments or 

 machines, of iron and steel, and giving very tasteful effects, are 

 produced by simply carrying the oxidation and resulting dis- 

 coloration to different degrees in the several parts treated. The 

 ranges of color obtainable by proper manipulation and treatment 

 being all the way between that of the lirilliancy of the natural 

 and polished surface, through the several tints of pale straw, 

 light, dark, and reddish brown, and purple, to blue, of a very 

 beautiful and agreeable tint, and this without sacrificing much 

 of the brilliancy of the originally finished or polished surface. 



The extremely thin films of oxidation thus produced do not, 

 however, possess much durability, and a moderate amount of 

 rubbing, or wear, suffices to remove it, and exposes anew the 

 natural color and surface of the metal. 



But if, instead of stopping the operation at this stage just 

 named, we continue the treatment, increasing the heat, with a 

 free access of a suitable oxidizing agent, a considerable coating 

 of the superoxidation may be olitained, and the utility of the 

 treatment as a means of protecting the article from natural 

 deterioration greatly improved. 



