1-38 JEmployment ofFlalina in Porcelain Painting. 



lows : — I dissolve cnide platina in aqua regia, and precipitate 

 it by a saturated solution of sal ammoniac in water. The 

 red crystalline precipitate thence produced is dried, and 

 beino; reduced to a very fine powder is slowly brought to a 

 red heat in a glass retort. As the volatile neutral salt, com- 

 bined with the platina in this precipitate, becomes sub- 

 limated, the metallic part remains behind in the form of 

 a gray soft powder. This powder is then subjected to the 

 same process as gold ; that is to say, it is mixed with k 

 small quantity of the same flux as that used for gold, and 

 being ground with oil of spike is applied with a bnish to the 

 porcelain; after which it is burnt-in under the muffle of an 

 enameller's furnace, and then polished with a burnishing 

 tool. 



The colour of platina burnt into porcelain in this man- 

 ner is a silver white, inclining a little to a steel gray. If the 

 platina be mixed in different proportions with gold, different 

 shades of colour may be obtainetl ; the gradations of which 

 may be numbered from the white colour of unmixed pla- 

 tina to the yellow colour of gold. Platina is capable of re- 

 ceiving a considerable addition of gold before the transition 

 from the white colour to yellow is perceptible. Thus, for 

 example, in a mixture of four parts of gold and one of 

 platina, no signs of the gold were to be observed, and the 

 white colour could scarcely be distingui>-hed from that of 

 unmixed platina : it was onlv when eight parts of gold to 

 one of platina were employed that the gold colour as^umcd 

 the superiority. 



I tried, in the like manner, different mixtures of platina 

 and silver ; but the colour produced was dull, and did not 

 seem proper for painting on porcelain. 



Besides this method of buniinj-in platina in substance 

 on porcelain, it may be emploved mso in its dissolved state ; 

 in which case it gives a different result both in its colour 

 and splendour. 'Vhc solution of it in aqua regia is evapo- 

 rated, and the thickened residuum is then applied several 

 times in succession to the porcelain. The metallic matter 

 thus penetrates into the substance of the porcelain itself, 

 and forms a metallic mirror of the colour and splendour of 

 polished steel *. 



• At the time this paper was read in the Royal Academy of Science;, 

 the author exhibited several patterns of porcelain oriiamentcd in tlift 

 toauuLi-, v.hicli had been made in die rojal wuiicivitory. 



XX. Ad' 



