58 
ON DEAD-SILVERING PORCELAIN. 
the brilliancy of the surrounding colours is deteriorated, and 
the friction, however carefully the cleansing may be effected, 
carries off a portion of the metal, which is necessarily laid 
on very thin. 
By M. Rousseau's very simple process, the silver is com- 
pletely protected from the injurious action of the sulphur, 
iu whatever quantity and in whatever state it may be. 
This statement is proved by various facts. The Ceramic 
Museum at Sevres has possessed, since the year 1845, speci- 
mens which were placed thereby M.'Rousseau at that time, 
and at the end of eighteen months they did not appear to 
have undergone any change. As it was not evident, how- 
ever, that they had been exposed to any sulphurous exha- 
lations, while there, I requested M. Rousseau to furnish 
me with an article for the purpose of submitting it to the 
action of sulphuretted hydrogen gas ; and he gave me the 
half of the tube of an opera-glass, which had been in use; 
this was exposed during several wrecks in the chemical 
laboratory, and the only alteration it underwent was that it 
was turned slightly yellow; but this was easily removed 
by a little soap and water. Shortly afterwards the same 
piece v*^as, together with the pretty little box now presented 
to the Society, fully exposed to the exhalations from a cess- 
pool, which was being emptied; and they were both, when 
taken out, in their present state of freshness. From this it 
became evident that M. Rousseau was in possession of the 
secret of giving to dead silver (which is much more easily 
affected by vapours than burnished silver) the power of 
resisting the deleterious action of the strongest hydrosulphu- 
ric exhalations. 
This important object is effected by the employment of 
gold. A very thin layer of this metal is laid, by means of 
a brush, over the silver with which the porcelain is orna- 
mented, before firing it, when, by the help of a flux and a 
cherry-red heat, the two metals are fixed on the porcelain. 
