294 TEST OF THE GLAZE OF POTTEKY. 



Every necessa- Thus ki the present state of our knowledge it is far from 

 terv mav be i Impossible, that an artist perfectly acquainted witli it, and 

 made without improved by practice, should succeed in fabricatinfi^, as Mr. 

 any metal. Jousselin profejsses, three kinds of pottery, to snpply the 

 place, 1st, of close grained stone-ware, for containing li- 

 quids and other matters, with or without glazing : 2dly, of 

 less close grained stone-ware, with a brown glaze externally, 

 and a white enamel internally, for culinary utensils: and 

 3dly, of delfts and white earthen-wares, retaining both ele-? 

 gance of form and lustre of glazing, without employing any 

 metal. 

 Very cheap The enamel of which Mr. Jousselin announces the dis- 



^one *^ ^^' covery is entirely earthy, and composed of materials so 

 cheap, that the enamel, which now costs the manufacturer 

 at the rate of 320 franks for a certain quantity of ware, will 

 come to no more than 15 or 20. 



X. 



Process for proving the QuaHty of a Glaze of Earthen- 

 War^ *. 



Defects of Jl HE glaze of earthen-ware may hare several defects : it 

 glaze. jnay be scratched more or less readily by a hard body; weak 



acids, such as vinegar, lemon-juice, verjuice, &c., may at- 

 tack and dissolve the lead it contains ; or oily substances 

 standing long on it may produce the same effect, stain it, 

 and render it dull. 



tific'al feldt- that afforded me ' y the feldtspar of Baveno, by urging to fusion in a 

 spar. platina crucible a mixture of 62 parts silex, 16 alumine, 10 lime, and 



Porcelain with- 12 i/otjsh. I have likewise made, without kaolin, a biscuit having the 

 out kaolin. hardness, semitransnarsncy, and grain of porcalain, by giving the pro- 

 per d-'gre3 of baking to a paste composed of 50 parts s.Iex, 20 alumine, 

 24Tnagne-»ia, and 6 lime I need not say, that it would be very easy to 

 employ the same proportions of silex and alumine, by choosing a good 

 clay, without being oblige^ to have recourse to the decomposition of 

 «lum for the earth. 



• Soonini's Bibliotheque PhysicQ^6cononiique, July, 1807, p. 43. 



To 



