on the high firing to which it has been subjected. For this purpose,
rejecting the common clays of his neighbourhood, he sent as far as
Dorsetshire and Devonshire for the whiter and purer pipe-clays of those
counties. For the siliceous ingredient of his composition he made choice
of chalk-flints, calcined and ground to powder.

It might be supposed that white sand would have answered his purpose
equally well, and have been cheaper; but, being determined to give the
body of his ware as great a degree of compactness as possible, it was
necessary that the materials should be reduced to the state almost of an
impalpable powder; and calcined flints are much more easily brought to
this state by grinding than sand would be. The perfect and equable
mixture of these two ingredients being a point of great importance, he
did not choose to trust to the ordinary mode of treading them together
when moist, but having ground them between stones separately with water
to the consistence of cream, he mixed them together in this state by
measure, and then, evaporating the superfluous water by boiling in large
cisterns, he obtained a composition of the most perfect uniformity in
every part. By the combination of these ingredients, in different
proportions, and exposed to different degrees of heat, he obtained all
the variety of texture required, from the bibulous ware employed for
glazed articles, such as common plates and dishes, to the compact ware
not requiring glazing, of which he made mortars and other similar
articles. The almost infusible nature of the body allowed him also to
employ a thinner and less fusible glaze, that is, one in which no more
lead entered than in common flint glass, and therefore incapable of
being affected by any articles of food contained or prepared in such
vessels. With these materials, either in their natural white or
variously coloured--black by manganese, blue by cobalt, brown and buff
by iron--he produced imitations of the Etruscan vases, and of various