ENAMELLING. 



It has been remarked, that when soda 

 and potash have been introduced, the co- 

 lours scaled, so that they cannot be used 

 as fluxes. These alkalies, being vola- 

 tilized, abandon the colours which can- 

 not adhere to the glaze by themselves. 



It has been observed, that other co- 

 lours are likewise prepared, which be- 

 ing laid upon the general surface, are 

 fused by the same fire as bakes the por- 

 celain. These colours are but few, be- 

 cause there are few metallic oxides that 

 can support such a fire without being vo- 

 latilized or discoloured. Their solvent 

 is the feldspar. As they incorporate 

 with the glaze they never crack, and are 

 more brilliant. 



The third receptacle of metallic vitri- 

 fiable colours is glass without lead. 



The application of these colours con- 

 stitutes the art of painting upon glass ; 

 an art much practised in former ages, but 

 which was, till lately, supposed to be 

 lost, because out of fashion. It, however, 

 too immediately depends on the art of 

 painting on enamel and porcelain to be 

 lost. Descriptions of the processes may 

 be found in different books. 



A book, entitled " L'Origine de Part 

 de la Peinture sur Verre," published at 

 Paris in the year 1693, and " Le Traite" 

 de I'art de la Verriere," by Neri and 

 Kunckel, seem to be the first works con- 

 taining complete descriptions of this art. 

 Those published since, even the great 

 work of Leviel, which constitutes part 

 of " Les Arts et Metiers," of thefFrench 

 academy, and of the " Encyclopedic Me- 

 thodique," are only compilations from 

 the two former works. 



It is somewhat remarkable, that if we 

 follow the processes exactly as they are 

 described in these works, as our author 

 has done with some of them, the colours 

 of which they pretend to give the re- 

 ceipt, would never be fabricated. They 

 only serve to show an able practitioner 

 the method, and leave it to him to cor- 

 rect or make additions. This was found 

 to be the case by Citizen Meraud, who 

 was engaged to prepare them for the 

 manufactory of Sevres. He was obliged 

 to make the colours for painting on glass 

 rather from his own experience, than 

 from the instructions in the work just 

 mentioned. 



The materials and fluxes which enter 

 into the compositions of the colours for 

 painting on glass are, in general, the 

 same as those applied to porcelain. They 

 vary only in their proportions; but a 

 great number of the colours used for 



VOT,.V 



enamel and porcelain cannot lie applied 

 on glass; many of them, when seen by 

 transmitted light, entirely change their 

 aspect, and exhibit an obscure tint, 

 which can be of no use when deprived of- 

 the white ground which throws them out. 

 We shall point out these when we treat 

 of the colours in particular. Those co- 

 lours which can be used on this body 

 sometimes change in the baking, and ac- 

 quire a great transparency. They are 

 generally beautiful only when placed be- 

 tween the eye and the light, and they 

 answer the purpose intended in painting 

 glass. 



There is more difficulty in baking- 

 plates of coloured glass than is common- 

 ly thought. The bending of the piece 

 and the alteration of the colours are to be 

 avoided. All the treatises we have con- 

 sulted recommend the use of gypsum. 

 This method sometimes succeeded with 

 Brougniart, but generally the glass be- 

 came white, and cracked in all direc- 

 tions. It appears, that the glasses which 

 are too alkaline, and which are far the 

 most common in clear white glasses, are 

 attacked by the hot sulphuric acid of the 

 sulphate of lime. He was able with ease 

 to bake much larger glasses than any 

 before painted, by placing them on very 

 smooth plates of earth or unglazed por- 

 celain. 



Concerning the several particular Colours. 



After having collected the several 

 phenomena which each class of verifiable 

 colours offer, with regard to the bodies 

 on which they are placed, we must shew 

 the particular and most interesting phe- 

 nomena, which every principal species 

 of colours employed on tender porcelain, 

 on glass, and in the fire that bakes the 

 porcelain, present. 



Concerning- the Reds, Purples, and Violets, 

 obtained from Gold. 



The carmine-red is obtained from the 

 purple precipitate of Cassius. It is mix- 

 ed with about six parts of its flux, and 

 this mixture is directly employed without 

 being first fused. It is then of a dirty 

 violet, but acquires the beautiful car- 

 mine by baking. It is however very deli- 

 cate ; a little too much heat or carbonat- 

 ed vapours easily spoil it ; yet it is more 

 beautiful when baked with charcoal 

 than with wood. 



This colour, and the purple, which dif- 



C 



