ENAMELLING. 



in a similar manner. 3. Four parts of 

 fluorspar, four of gypsum, and one of li- 

 tharge, melted into a straw-coloured 

 glass, ground and applied in the same 

 way, required a much stronger heat. 

 4. Five parts of fluor spar, five of gyp- 

 sum, two of minium, two of flint glass, 

 half a part of borax, the same of oxide 

 of tin, and one-twenty-fifth of a part of 

 oxide of cobalt, melted together, made an 

 enamel, which, when ground and applied 

 as the others, fused with a less degree of 

 heat. This, M. Rinman imagines, would 

 have been acted upon in length of time 

 by sulphuric acid. The oxide of cobalt 

 was prepared by saturating a solution of 

 cobalt in aqua-fortis with common salt, 

 and evaporating to dryness 



As these would not do for iron, he 

 tried the following : 1. minium, nine 

 parts ; flint glass, six ; pure potash, two; 

 nitre, two ; borax, one ; were ground to- 

 gether, put into a covered crucible, 

 which they only half filled, and fused into 

 glass. This poured out on a piece of 

 marble, quenched in water, powdered 

 and made into a thin paste, was laid on 

 both sides of an iron vessel. After hav- 

 ing been dried and heated gradually, the 

 vessel was put under a muiHe, well heated 

 in an assaying furnace, and in half a mi- 

 nute the enamel melted. The vessel 

 being then withdrawn, was found ena- 

 melled of a beautiful black colour, which 

 appeared to be ov ing to a thin layer of 

 oxided iron seen through the transpa- 

 rent glaze. 2. The same, with one hun- 

 dreth part of oxide of cobalt prepared 

 as above, covered the vessel more per- 

 fectly with a blue enamel. 3. The same, 

 ground with potters' white lead, which 

 consists of four parts of lead and one of 

 tin, produced a very smooth grey enamel 

 more firm and hard than the preceding. 

 A small quantity of red oxide of iron 

 gave it a fine dark red colour. 4. Flint 

 glass, twelve parts ; minium, eighteen ; 

 potash, four; nitre, four ; borax, two ; 

 oxide of tin, three ; oxide of cobalt, 

 one eighth of a part; gave a smooth pearl 

 coloured enamel, not brittle or subject 

 to crack, and capable of enduring sud- 

 den changes of heat and cold, as well as 

 the action of oils, alkalies, and weak 

 acids : but it cannot resist the stronger 

 vegetable acids, and still less the mine- 

 ral. 



These enamels were applied only on 

 hammered iron, cast iron being too thick 

 to be heated with sufficient quickness. 

 But they have been applied to the thin 

 cast vessels in England. It seems unne- 



cessary to add, none of them will bear 

 hard blows ; and this is perhaps the rea- 

 son why they have not been more used 

 with us. 



The application of enamel colours to 

 glass or earthenware constitutes a pecu- 

 liar branch of the art. M. Brougniart, 

 of the porcelain manufactory at Sevres, 

 has given a good account of them. (Ni- 

 cholson's Journal, Vol. HI. 4to.) 



These bodies may be divided into three 

 very distinct classes, from the nature of 

 the substances that compose them, the 

 effects produced on them by the colours, 

 and the changes they undergo. These 

 are, 1. enamel ; soft porcelain, and all 

 the glazes, enamels, or glasses, which 

 contain lead in any considerable quantity. 

 2. Hard porcelain, or such as is glazed 

 with feldspar. 3. Glass, in which there is 

 no lead, such as the common window 

 glass. The principles of composition of 

 these colours, and the general phenome- 

 na they present on these three grounds 

 or supporters, are regularly treated of. 



Colours in enamel painting have been 

 longest known. Enamel is a glass ren- 

 dered opaque by oxide of tin, and very 

 fusible by the oxide of lead. It is this 

 last, which, in particular, gives it proper- 

 ties very different from those of the other 

 excipients of metallic colours. Hence all 

 the glasses and glazes which contain lead 

 have the properties of enamel, and what 

 we may assert of the one will apply to the 

 other with very little difference. 



Such are the white and transparent 

 glazes of Dutch or Delf ware; and the 

 glaze of the porcelain called soft ware. 



This porcelain, the first made in 

 France, particularly at Sevres, and in- 

 deed for a long time almost exclusively 

 at that manufactory, has for its base vi- 

 treous frit, nearly opaque, capable of be- 

 ing acted upon by marie, and its glaze is 

 very transparent glass, containing much 

 lead. 



The colours made use of are the same 

 as those for enameling, consequently the 

 changes these colours undergo in enamel 

 must take place in this species of porce- 

 lain : the causes of the change being the 

 same in both. 



The colours for enamel and soft por- 

 celain require less flux than the others, 

 because the glass on which they are 

 placed softens sufficiently to be pene- 

 trated by them. 



This solvent may be either the mix- 

 ture of glass of lead and pure silex, call- 

 ed rocaille, or this same glass mixed with 

 that of borax. 



