S60 Dr Traill cm the Mineralogy of Halkin Mountain, 
through water, to free it from any intermixture of gritty sand, 
is dried and sold at Flint for £ 3, 12s. per ton. It is now 
greatly prized by our potters, for the beautiful quality of the 
ware produced, by mixing with plastic clays, containing more 
alumina. By itself, it evidently has too much silica to form a 
perfect biscuit. When the attempt is made, it produces one of 
a dazzling whiteness ; but this may be scraped with a knife, and 
Jiies vfhQXi glazing is attempted. If, however, cambria be mix- 
ed in due proportion with common potters-clay, it forms a stone- 
ware of superior colour even to our finest Worcestershire china, 
and infinitely more beautiful than the best stoneware heretofore 
made at the Staffordshire potteries. The following comparative 
statement of the expence of the materials commonly used for 
the best blue printed stoneware, and of the mixture of cambria 
employed for the same purpose, as all the ingredients now cost 
in Staffordshire, may be interesting. Washed cambria is ship- 
ped at 72s. per ton, with, carriage, &c. 14so. 6d. =z £4<i 6: 6 per 
ton 
No. 1. 
Cambria mixture or Body. 
40 cwt. Cambria *, - £ 8 13 U’ 
20 cwt. Blue Clay, - 2 5 0 
5f cwt. Powdered Flint, 1 14 0 
1 cwt. Cornish Stone •}•, 0 5 0 
66| cwt. £12 17 0 
Or £3, 16s. per Ton, 
No. 2. 
Common Body. 
1 cwt. Flint, - £ 0 5 0 
3 cwt. Blue Clay, - 0 6 9 
1 cwt, Cornish Clay, 0 6 0 
5 cwt. £0 17 9 
Or £3, 11, per Ton. 
Each ton of the common body is calculated to afford 800 
dozens plates, weighing rather more than 8 lb. per dozen. If 
we suppose that a ton of the cambria mixture will yield as many 
plates, they will be rather less than one farthing per dozen dearer 
than the common blue ware ; while they even surpass Cliina in 
beauty of colour, and, from the smoothness of surface, may be 
neatly ornamented with painting and gilding. In some manu- 
factories,. the following mixtures are employed : 
• When so large a proportion of cambria is used, the ware requires a felspar 
glaze ; but the common lead-glaze may be employed when there is a larger pro- 
portion of plastic clay than one-half of the whole mixture. 
-j- This is a disintegrated granite, containing some mica, which impairs the 
colour of the biscuit. 
