Dagucrreotye images andphotographic impressions may be reproduced in the following manner The image is received in the camera obscura on a plate of silver, strongly iodized ; the plate is then exposed to the vapour of mercury, but not to the action of hyposulphite of soda. It is then plunged into a solution of sulphate of cop per, placing it for a few instants in com munication with the negative pole of a battery and closing'the circuit with a pla tina wire. The copper deposits itself only on the parts covered by the mercury, the iodide of silver not being a conduc tor of electricity. The plate is then washed with distilled water, then with the hyposulphite of soda to remove the iodide, and quickly dried over a spirit lamp. The image, in which the copper represents the light parts and the silver dark, is transferred, at least the copper, on very thin plates of gelatine. An in verted image is thus obtained, since the copper which is opaque, represents the light parts. The transfer is made by run ning on the plate a clear solution of gela tine, and allowing it to dry; after which the gelatinous foil on which the copper adheres, is attached. The negative proof obtained, the next part of the process is; to re-produce a positive image ; for this purpose a sheet of photographic paper is taken, on which is carefully applied the proof in gelatine the face on winch is the copper underneath. The whole is then exposed to diffused light during a quar ter of an hour ; the paper is then plunged into water in order to be washed, and then into a solution of hyposulphite of soda to remove the salt of silver ; it is then washed in a large quantity of water and dried,, by this a perfect and positive reproduction of a daguerreotype image is obtained. If it be desired to obtain the reproduction of a drawing or an engrav ing, a negative proof is taken on a pre pared iodized plate, in placing it over the design or engraving and exposing the whole to the light. It is then passed through the mercurial process and the series of operations above described.
The following improvement in the pro cess of Daguerreotyping has just been discovered by Niepce, the first discove rer of the art. The engraving is to be submitted to vapor of iodine (at a tempe rature of 15 or 20i degrees) during about ten minutes ; a longer time is necessary if the temperature be less elevated; ten grammes of iodine to be used per square of 4 inches. The paper intended to re ceive the impression is to be covered with a coat of paste, taking care previ ously to have it moistened with water containing one degree of pure sulphuric acid. The proofs, after being pressed with a linen cloth, present a design of admirable purity. These impressions, taken on paste will, however, in drying, become vaporous ; but if taken on paper prepared with one or two layers of starch, the design will not only be clear, but will preserve much better. What is most extraordinary is, that many impressions may be taken from the same print with out submitting it to a new preparation— the last proofs being always the clearest. Designs of various colors may thus be obtained according as the paste is more or less boiled, or according to the quanti ty of acid used. Proofs may also be taken on different metals by observing the tbl `towing precaution. In submitting the engraving to the vapor of iodine, care should be taken to have it perfectly dry, in order that the white portions of it may become impregnated. In this case it should be exposed but a few minutes to the vapor. Let it be afterwards applied, without wetting it, to a plate of silver, and then placed under a press • at the end bf five or six minutes there will be a most faithful reproduction of the original. By afterwards exposing the plate to the va por of mercury, a proof similar to that of a daguerreotype is obtained.
It has been rumored, that at a meeting of the French Academy of Sciences, M. Niepce had declared his capability of taking the pictures in the natural colors ; his process has not yet reached this country.