Noxid.
New Process for Positive Proofs.—I have tried a method of preparing my paper for positive proofs, which, as I have not seen it mentioned as employed by others, and the results appear to me very satisfactory, I am induced to communicate to you, and to accompany by some specimens, which will enable you to judge of the amount of success.
I use a glass cylinder, with air-pump attached, such as that described by Mr. Stewart as employed by him for iodizing his paper. I put in this the salt solution, and that I use is thus composed: 2 drachms of sugar of milk, dissolved in 20 ounces of water, adding—
Chloride of barium 15 grs.
Chloride of sodium 15 grs.
Chloride of ammonium 15 grs.
In this I plunge several sheets of paper rolled into a coil (taking care that they are covered by the solution), and exhaust the air. I leave them thus for a few minutes, then take them out and hang them up to dry; or as the sheets are rather difficult to pin, from the paper giving way, spread them on a frame, across which any common kind of coarse muslin or tarletan, such as that I inclose, is stretched.
I excite with ammonio-nitrate of silver, 30 grains to 1 ounce of water, applied with a flat brush.
I fix in a bath of plain hypo. of the strength of one-sixth. The bath in which the inclosed specimens were fixed has been in use for some little time, and therefore has acquired chloride of silver.
I previously prepared my paper by brushing it with the same salt solution, and the difference of effect produced may be seen by comparing a proof so obtained, which I inclose, with the others. This latter is of rather a reddish-brown, and not very agreeable tint. I have inclosed the proofs as printed on paper of Whatman, Turner, and Canson Frères, so as to show the effect in each case. The advantages which the mode I have detailed possesses are, I think, these: