Chelsea ware, besides bearing a very imperfect similarity in body to
the Chinese, admitted only of a very fusible lead glaze; and in the
taste of its patterns, and in the style of their execution, stood
as low perhaps as any on the list. The china works at Derby come, I
believe, the next in date; then those of Worcester, established in
1751: and the most modern are those of Coalport, in Shropshire; of the
neighbourhood of Newcastle, in Staffordshire, and in other parts of
that county.

The porcelain clay used at present in all the English works is
obtained in Cornwall, by pounding and washing over the gray
disintegrated granite which occurs in several parts of that county: by
this means the quartz and mica are got rid of, and the clay resulting
from the decomposition of the felspar is procured in the form of a
white, somewhat gritty powder. This clay is not fusible by the highest
heat of our furnaces, though the felspar, from the decomposition of
which it is derived, forms a spongy milk-white glass, or enamel, at
a low white heat. But felspar, when decomposed by the percolation of
water, while it forms a constituent of granite, loses the potash,
which is one of its ingredients to the amount of about 15 per cent,
and with it the fusibility that this latter substance imparts.

The siliceous ingredient is calcined flint; and in some of the
porcelain works, (particularly, I believe, those at Worcester,) the
soapstone from the Lizard-point, in Cornwall, is employed. These are
all the avowed materials; but there is little doubt that the alkalies,
or alkaline earths, either pure or in combination, are also used,
in order to dispose the other ingredients to assume that state of
semi-fusion characteristic of porcelain.