The fixing, of course, modifies considerably the tone of the proof, but almost any desired shade { 397} may be attained by following the plan of MR. F. M. LYTE, published in "N. & Q.," provided the negative is sufficiently intense to admit of a considerable degree of over-printing.
It is a fact which appears to be entirely overlooked by many operators, that the _intensity_ of the negative is the chief agent in conducing to black tones in the positive proof; and it is almost impossible to produce them if the negative is poor and weak: and the same observation applies to a negative that has been _over_-exposed.
_Cement for Glass Baths._--The best I have tried is Canada balsam. My baths I have had in use five years, and have used them for exciting, developing hypo. and cyanide, and are as good as when first used.
_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.