There is another source of clay, and that of the finest kind, from decomposed granite, this is of a snowy white and mixed with mining particles of mica, of this kind is an earth from the country of Cherokees. Other kinds are from less pure lavas; Mr. Ferber asserts that the sulphurous steams from Mount Vesuvius convert the lava into clay. "The lavas of the antient Solfatara volcano have been undoubtedly of a vitreous nature, and these appear at present argillaceous. Some fragments of this lava are but half or at one side changed into clay, which either is viscid or ductile, or hard and stoney. Clays by fire are deprived of their coherent quality, which cannot be restored to them by pulverization, nor by humectation. But the sulphureous Solfatara steams restore it, as may be easily observed on the broken pots wherein they gather the sal ammoniac; though very well baked and burnt at Naples they are mollified again by the acid steams into a viscid clay which keeps the former fire-burnt colour." Travels in Italy, p. 156. NOTE XXI.--ENAMELS. _Smear'd her huge dragons with metallic hues, With golden purples, and cobaltic blues;_ CANTO II. l. 287. The fine bright purples or rose colours which we see on china cups are not producible with any other material except gold, manganese indeed gives a purple but of a very different kind. In Europe the application of gold to these purposes appears to be of modern invention. Cassius's discovery of the precipitate of gold by tin, and the use of that precipitate for colouring glass and enamels, are now generally known, but though the precipitate with tin be more successful in producing the ruby glass, or the colourless glass which becomes red by subsequent ignition, the tin probably contributing to prevent the gold from separating, (which it is very liable to do during the fusion; yet, for enamels, the precipitates made by alcaline salts answer equally well, and give a finer red, the colour produced by the tin precipitate being a bluish purple, but with the others a rose red. I am informed that some of our best artists prefer aurum fulminans, mixing it, before it has become dry, with the white composition or enamel flux; when once it is divided by the other matter, it is ground with great safety, and without the least danger of explosion, whether moist or dry. The colour is remarkably improved and brought forth by long grinding, which accordingly makes an essential circumstance in the process.