my T2889 
xv. Reflections on the ‘eoang of Earthén-Ware, and the 
Refults of the Analyfis of fome Earths and common Kinds 
of Earthen-Ware. By C. VAUQUELIN*. 
Four things may occafion the difference in the quali- 
ties of earthen-ware: 1ft, the nature or compofition of the 
matter: 2d, the mode of preparation; 3d, the dimenfions 
given to the yeffels; 4th, the baking to which they are fub- 
jected. By compofition of the matter, the author under- 
ftands the nature and proportions of the elements of which it 
is formed. Thefe elements, in the greater part of earthen- 
ware, either valuable or common, are filex, argil, lime, and 
fometimes a little oxyd of iron. Hence it is evident that it 
is not fo much by the diverfity of the elements that good 
éarthen-ware differs from bad, as by the proportion in which 
they are united. Silex or quartz makes always two-thirds at 
leaft of earthen-ware ; argil or pure clay from a fifth to a 
third; lime from 5 to 20 parts in the hundred; and iron from 
© to 12 or 15 parts in the hundred. Silex gives hardnefs, 
infufibility, and unalterability ; argil makes the pafte pliable, 
and renders it fit to be fobs moulded, and turned at 
pleafure. It poffeffes at the fame time the property of being 
partially fufed by the heat which unites its parts with thofe 
of the filex; but it muft not be too abundant, ‘as it would 
render the earthen-ware too fufible and too brittle to be ufed 
over the fire. 
Hitherto it has not been proved by experience that lime 
is neceflary in the compofition of pottery: and if traces of * 
it are conftantly found in that fubftance, it is becaufe it is 
always mixed with the other earths, from which the wafhings 
and other manipulations have not been able to’ feparate it. 
When this earth, however, does not exceed five or fix parts 
in a hundred, it appears that it is not hurtful to the quality 
of the pottery; but if more abundant, it renders it too fu- 
fible. 
The oxyd of iron, befides the inconvenience of communi- 
cating a red cr brown colour, according to the degree of 
* Bulletin des Sciences, Vol. Ul. No, 2. . 
4 baking, 
ay eae 
