This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Applying The Retouching Dope To The Negative.
The plate must be perfectly dry before applying any medium. In applying the dope to the negative the smallest quantity must be used, for if too much is employed it it will require a longer time for it to dry and the over-charge of dope may show in the print. A drop or two applied to the space you want to retouch, or just enough to give a tooth, is all that is necessary.
26. A simple way to apply the dope would be to prepare your medium in a two ounce, wide mouthed bottle, having a cork stopper. In the under side of the cork insert a wooden toothpick. By placing the cork stopper into the bottle, the toothpick is always immersed in the dope, and when you want to prepare a negative all that is required is to withdraw the stopper and touch the point of the toothpick to the surface of the film. Each touch will leave a drop of the dope, and from 1 to 3 drops is sufficient for a space 3 inches in diameter.
27. After dropping on the dope, return the cork to the bottle and spread the solution with a small tuft of absorbent cotton (or Canton flannel cloth), lightly rubbing the parts to be retouched in a circular motion until the
dope begins to feel tacky, at which time rub a little harder until the surface becomes smooth. Should the dope evaporate at any time and become so thick and sticky that it is difficult to use and spread on the negative, the addition of pure turpentine will bring it back to its normal condition. As the fluid dries quickly when applied to the negative, you may have to try several times in order to secure the desired result. In case it does dry before you get it rubbed, slowly add a little more fluid and repeat the operation.
28. The surface, when properly prepared, must not appear sticky nor tacky, but slightly glossy. If it is tacky, or, in other words, too thick, too much of the fluid has been left on the plate and the lead will take too readily. If too little of the fluid is left on the plate, you will not have sufficient tooth and the pencil will hardly make a mark. After a little practice you will be able to prepare the plate properly.
Retouching Varnish. Where the retouching varnish is employed in place of the dope, Hammer's Retouching Varnish will be found by far the most satisfactory medium to employ. The following formula is an excellent one for preparing a similar varnish:
The ether cuts the gum and the latter must be thoroughly dissolved.
30. A mortar and pestle will be very serviceable in preparing this medium. After the gum is thoroughly dissolved it is poured very slowly (drop by drop) into 6 ounces of gasoline. Do not stir the gasoline while adding the gum, but allow the gum solution to mix with the gasoline itself. By adding the gum slowly drop by drop, the gasoline will take care of the gum and properly dissolve it. After the gum solution is added, set in a cool place, undisturbed for at least 12 hours before using. Under no circumstances should this preparation be removed or disturbed until sufficiently seasoned, ready for use.