The demand all through the country by skillful decorators for the pottery forms to work upon, points to still greater extensions in this business of making our own china, and to the employment and good pay of more thousands than are now employed in it. A collection of American china, terra cotta, etc., begun at this time and added to from year to year, will soon be a most interesting cabinet. Both in the eastern and western manufactories ingenious workers are rediscovering and experimenting in pastes and glazes and colors, simply because there is a large demand for all such, and they can be supplied at prices within the reach of most buyers. It needs only to point out this flourishing state of things, through the "let-alone" principle, which protection insures to this industry, to exhibit the threatened damage of the attempt, under cover of earthenware duties, to get a little free trade through at this session.--Philadelphia Public Ledger.
PHOTOGRAPHIC NOTES.
Mr. Warnerke's New Discovery.--Very happily for our art, we are at the present moment entering upon a stage of improvement which shows that photography is advancing with vast strides toward a position that has the possibility of a marvelous future. In England, especially, great advances are being made. The recent experiments of our accomplished colleague, Mr. Warnerke, on gelatine rendered insoluble by light, after it has been sensitized by silver bromide and developed by pyrogallic acid, have revealed to us a number of new facts whose valuable results it is impossible at present to foretell. It seems, however, certain that we shall thus be able to accomplish very nearly the same effects as those obtained by bichromatized gelatine, but with the additional advantage of a much greater rapidity in all the operations. In my own experiments with the new process of phototypie, I hit upon the plan of plunging the carbon image, from which all soluble gelatine had been removed, into a bath of pyrogallic acid, in order to still further render impermeable the substance forming the printing surface. I also conceived the idea of afterward saturating this carbon image with a solution of nitrate of silver, and of subsequently treating it with pyrogallic acid, in order to still further render impermeable the substance forming the printing surface. But the process described by Mr. Warnerke is quite different; by means of it we shall be able to fix the image taken in the camera, in the same way as we develop carbon pictures, and afterward to employ them in any manner that may be desirable. Thus the positive process of carbon printing would be modified in such a manner that the mixtures containing the permanent pigment should be sensitized with silver bromide in place of potassium bichromate. In this way impressions could be very rapidly taken of positive proofs, and enlargements made, which might be developed in hot water, just as in the ordinary carbon process, and at least we should have permanent images. Mr. Warnerke's highly interesting experiments will no doubt open the way to many valuable applications, and will realize a marked progress in the art of photography.
Method for Converting Negatives Directly into Positives.--Captain Bing, who is employed in the topographic studios of the Ministry of War, has devised a process for the direct conversion of negatives into positives. The idea is not a new one; but several experimenters, and notably the late Thomas Sutton, have pointed out the means of effecting this conversion; it has never, however, so far as I know, been introduced into actual practice, as is now the case. The process which I am about to describe is now worked in the studios of the Topographic Service. The negative image is developed in the ordinary way, but the development is carried much further than if it were to be used as an ordinary negative. After developing and thoroughly washing, the negative is placed on a black cloth with the collodion side downward, and exposed to diffuse light for a time, which varies from a few seconds to two or three minutes, according to the intensity of the plate. Afterward the conversion is effected by moistening the plate afresh, and then plunging it into a bath which is thus composed:
Water 700 cub. cents.
Potassium bichromate 30 grams.
Pure nitric acid 300 cub. cents.
In a few minutes this solution will dissolve all the reduced silver forming the negative; the negative image is therefore entirely destroyed; but it has served to impress on the sensitive film beneath it a positive image, which is still in a latent condition. It must, therefore, be developed, and to do this, the film is treated with a solution of--
Water 1,000 grams
Pyrogallic acid 25 "
Citric acid 20 "
Alcohol of 36° 50 cub. cents.
The process is carried on exactly as if developing an ordinary negative; but the action of the developer is stopped at the precise moment when the positive has acquired intensity sufficient for the purpose for which it is to be used. Fixing, varnishing, etc., are then carried on the usual way. The great advantage of this process consists in the fact of its rendering positives of much greater delicacy than those that are taken by contact; and, on the other hand, by means of it we are able to avoid two distinct operations, when for certain kinds of work we require positive plates where a negative would be of no service. M. V. Rau, the assistant who has carried out this process under the direction of Captain Bing, has described it in a work which has just been published by M. Gauthier-Villars.