[ 244 ]

From the different effects of different materials on thesurface of the porcelain, I have endeavoured to add sqmeembellishment to this kind of ware. By covering theoutside of the glass vessel to be changed with powderedcharcoal, or with a mixture of powdered charcoal andwhite sand, and the inside with white sand alone, the por-celain vessel, resulting from the cementation, has provedof a deep black or a bright brown colour without, andof a tolerable whiteness within. By covering differentparts of the glass with different powders, as charcoal, whitesand, white clay, lime, and coloured earths, I have ob-tained, in one piece, variegations, not inelegant, of differ-ent shades of black, brown, grey and whitish, and withglossy and wrinkled veins. The above colours, with thebluish cast which the glass exhibits before the change iscompleted, are all that I have observed glass to receive bythe process of baking.

As the action of foot and charcoal on iron, in the con-version of iron into steel by baking, is promoted, and insome respects varied, by the admixture of a little sea salt,and of the saline ashes of wood, I made trial of the samecomposition for the baking of glass ; and as the inflamma-ble ingredients in this mixture could not fail to give ablack colour to the porcelain, I tried at the same time,in another crucible, wood ashes alone, which had beencalcined in a strong fire, to burn out all remains of theirinflammable matter, and reduce them to perfect white-ness.

The steel-making mixture did not answer so well asthe foot or charcoal by themselves : the glass did indeedbecome porcelain, but of a bad quality, all over blistered,with many cavities, and some of them very large, in theinternal part. The wood ashes, instead of changing the

I > glass