The Mirror of Literature, Amusement, and Instruction - Volume 19, No. 550, June 2, 1832 by Various
page 32 of 45 (71%)
page 32 of 45 (71%)
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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 |
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