If you use alum, do not tone so much, and use less gold, as the alum makes the prints two or three shades darker than the gold and hypo leaves them. - A. Hesler.
291. There are various other perplexities which will come up in the practice of photographic - printing, among which maybe mentioned the abrading or cracking of the surface of the prints after the are dried - sometimes called "woolliness;" the cockling or wrinkling of the pay under the pressure - frame, and finally a very bad defect, the distortion of the image caused by the contracting and stretchingof the paper. Good practical ideas on all those are given in the notes, to which be pleased to refer.
291. The cause of cracks or flaws lies in the excessive dryness of the albumenized paper during the various photographic operations. With the exercise of a little attention and practice, it is possible to tell whether the unsensitized paper is inclined to crack. Extraordinary brilliancy is generally a sign of this weakness, although it must not by any means be inferred that all brilliant papers are open to this objection. The first condition is that the paper should not be preserved in too dry a state, nor allowed to roll up. Very dry paper, on being sensitized, possesses, besides, the disadvantage of repelling the silver solution, which hangs upon the surface of the paper in drops. After sensitizing, the paper must not be dried too rapidly nor too highly, and should be suspended from two corners to prevent its rolling up, a precaution also requiring strict attention when the pictures are taken from the water after washing. Finally, they should be mounted in a slightly moistened condition, as, when kept in rolls in a dry state, the defects above referred to are easily developed on rubbing the paper-folder over the albumenized surface. - Oskar Pfeiffer.
The following, if not one of the " wrinkles," is one way to avoid them. In making prints from large plates, the printer is often troubled by wrinkles or cockles in the middle of the sheet which no amount of padding or pressure in the frame will bring in contact with the negatives. To remedy this, after silvering, and before the paper is thoroughly dry, fasten the sheet by the corners to the fuming - frames, or locking these to a large board or anything that will keep it out straight, and allow it to get as dry as usual. Then give the middle of the sheet an extra dry over a lamp or gas-stove, and the paper, instead of bagging in the centre, will have all its wrinkles near the outside, and, when printing, will be found to lie against the negative "as close as a cat to a hot brick." - J. L. Gihon.
Observe that the expansion and contraction are not equally proportioned to all dimensions of the bead, both being much greater in proportion to the breadth of the face than to its length, so that either print is distorted, which in the case of an equal mobility of the parts of the paper would not be; the paper contracts and expands nearly three times as much across the -narrow way of the sheet as in its length. This is an important, constantly present, and, it seems to me, unavoidable cause of photographic distortion. Let both of these heads be magnified to life size, in length, from the outer right-hand corner of the mouth to the inner corner of the right eye, two - and-a-quarter inches, and the divergence in width would become comparatively enormous. Let now the head be carefully traced by the hand, following the solar camera image of the negative, and a third scale of dimensions is produced. Print from the negative, in a solar camera, with the length of the paper placed across the width of the face, then another print with paper placed with its length parallel to the length of the face, and you have a fourth and fifth scale; under all conceivable conditions this cause of distortion remains. - W. J. Baker. 16