" To apply this process to porcelain, upon which material a direct picture is wanted as a permanent article, the process is the same, but the requirements differ.
" Some idea of the plan may be obtained when I state the neces sity which brought it about ; it was the desire to burn-in a photo graph on enam,e1 or porcelain : but a positive collodion picture will not sink into hard enamel ; it will burn away before the enamel ob tains heat enough to become soft. It will sink into soft enamel. The result, however, is so like a daguerreotype that I did not think it worth the trouble of continuing the work.
" When a collodion photograph is taken from a negative on white porcelain, the metallic deposit forms the dark part of the picture, and the white surface of the porcelain the whites of the picture.
" It is impossible to obtain good collodion pictures on unglazed porcelain, and the photograph will not stand the he,at, as before mentioned, which is required to sink-in the impression, so that, to make the picture pass through the kiln, it is necessary to go over the photograph with enamel colours.
" On engraving this kind of picture on porcelain, I have found, especially with Mr. Minton's beautiful white tiles, that when the
acid had acted too much, the picture still retained its hold of the porcelain and did not wash off as it does after the same action on glass ; and when it was dried, all the glaze was found to be eaten off, but still the lines of the photograph were fixed as fast as ever. This is worthy the attention of persons who are amdous to apply photography to porcelain.
" The point of interest, however, for the photographer is the follow ing :—If the porcelain is acted upon properly, those parts under the metallic lines are protected from the action of the acid, while the other parts are acted upon, so that the picture, after being eng,raved, is formed by the dull surface of the unglazed porcelain on the one part, and the brightness of the glazed on the other part. This is suffi cient to convince me, that if we had white tiles flashed,' as it is technically termed, with a dark vitrifiable colour, we should be able to obtain an engyaving with hydro-fluoric acid, a white picture on a dark ground, the acid eating out the bare parts of the proof, while those protected by the metallic deposit would retain the surface colour.