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dish, or yellowiso : these colours also resisted the jointaction of fire and air, equally with the preceding. Thebrowns and blacks were on some pieces very glossy andtolerably beautiful.

Different white earths gave different shades of whitish,greyish, or brownish; but none of them gave a purewhite, nor a whiteness equal to that of the internal partof the porcelain. It is difficult to distinguish precisely theeffect of particular earths, in this respect, from that ofthe degree of fire or other circumstances in the process :for of pieces of the fame bottle, which had been surroundedand baked with the the fame earth, some turned out ma-nifestly whiter than others. White sand, calcined flint,and gypsum, seemed in general to give the greatest white-ness, and tobacco-pipe clay the greatest brightness orglossiness, though this last, baking together in a lump uponthe porcelain, made the surface in some parts rough.

In this experiment, and in several repetitions of it, thesurface of some of the pieces proved rough like shagreen,that of some wrinkled like shrivelled leather, and of othersblistered or full of blebs. These appearances seem tohave depended more upon the fire having been too strongor too hastily raised, so as to make the glass soft or readyto melt, than on any particular quality of the materialswith which it was surrounded ; though it appeared alsothat some materials dispose to these imperfections morethan others. Pieces of one and the fame glass bottlehaving been baked, some with tobacco-pipe clay, andothers with quicklime, and with bone ashes, in the famedegree of fire, and for the fame length of time, the por-celain with the clay proved almost every where smooth andpolished as the glass was at first, while those with the limeand with the bone a so were all over wrinkled.

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