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.

(The principal processes are) the grinding and due mixture of the ingredients, in order to obtain a mass sufficiently plastic; the forming this mass on the wheel; the subsequent drying of the ware; the first firing, by which it is brought to the state of biscuit; the application of the firmer colours occasionally on the surface of the biscuit; the dipping the biscuit in the glaze; the second firing, by which the glaze is vitrified; the pencilling in of the more tender colours on the surface of the glaze; and the third and last firing that is given to the porcelain.

It is not for me to determine which of our English porcelains is the best; probably, indeed, one will be found superior in hardness, another in whiteness, a third in the thinness and evenness of the glaze, a fourth in the form of the articles, a fifth in the design, and a sixth in the colours.  In hardness and in fusibility, they are probably all inferior to the Dresden and to the Sevres porcelain; for pieces in biscuit and in white glaze, from both these manufactories, are imported in considerable quantities, in order to be painted and finished here.  But it is equally certain, that the last ten years have seen the commencement, and, in part, the completion, of such improvements in this fabric, as will probably place the English porcelains on an equality with the best of the continental European ones.

Advantage has recently been taken of the semi-transparency of porcelain biscuit to form it into plates, and to delineate upon it some very beautiful copies of landscapes and other drawings, by so adapting the various thicknesses of the plate as to produce, when held between the eye and the light, the effects of light and shadow in common drawings.  The invention originated in the ingenuity of our French neighbours.