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.
Strokes Of Lead Showing Too Prominently. Caused (a) by bearing on too heavily; (6) by using too soft a lead; or (c) by sitting too close to your work. (a) The pencil should be held loosely in the hand. (b) The beginner should use at least an HHH pencil, and after considerable practice may be able to use the HH. The change from the hard to the soft lead should not be made, however, until you have full control of the stroke. (c) Do not sit so close to the negative that each individual stroke is seen. Sit erect, with the eyes fully 18 to 24 inches from the negative.
Working Away From Highest Lights. When connecting little patches of work blend and connect each with the higher lights. Begin by working a very little, close to the highest point of light (until you blend the work even to it); then gradually blend away from it until the blending appears uniform toward the next stage of light. By blending downward, following the angle of light on the face, you avoid working in steps, as the work should be lighter as you near the lower or shadow portions.
Eliminating Transparent Spots Without The Lead Marks Showing. In order to accomplish this you must first work lightly. If the light stroke does not eliminate the spot go over it again, applying the lead a little heavier. You must remember that the retouching medium supplies the tooth by means of which the lead takes to the spot. When the lead is applied too liberally you will find yourself working on a lead surface which has become smooth and has no tooth, finally causing the lead-work to become somewhat transparent. You should judge the weight of the stroke by the density of the spot. If very transparent you may apply a heavier stroke than if only faintly visible. By applying a moderate amount of lead with each stroke you avoid overdoing the work. It is always advisable to apply the first few strokes lightly, until you can judge, by the results of the light strokes, how heavily you may apply the lead. When the lead is applied too heavily, the stroke will show on the surface (when viewed by transmitted light). It
is, therefore, better to work lightly over the spots several times than to have the strokes show. With very small spots you will find the mere dot of the pencil will be sufficient to eliminate it.
What Spots To Remove. The spots to remove are those which appear white or transparent in the negative. They may be freckles, pimples, blotches, wrinkles or any other blemishes on the face. After these spots have been removed you will find that other spots will make their appearance. These will also have to be eliminated, and it is their removal that is termed blending. Longer and more frequent strokes are employed for this part of the work, but you should be careful that the stroke does not go beyond the space you are blending. It is far better to use a short stroke and have perfect control of it, than to go to the other extreme and not secure the proper result.
Holding The Pencil Properly. The pencil should be held in the same manner as you would hold it when writing, but not as tightly. The strokes should be made freely and lightly. With a little practice you will soon adopt the position which is the most natural one for you to use.
Dope Seems Too Tacky. You have either applied too much dope; you have not rubbed it long enough to distribute it properly over the surface of the paper; or the dope has become too thick. One or two drops applied in the center of the face will be a sufficient quantity of the medium. It must be rubbed in a circular motion with a tuft of cotton until it is well distributed over the entire face. Gradually rub outward, continuing the circular motion, so there will be no perceptible line at the edge of the dope. The stopper should not be left off the bottle. If the medium should become thick, setting it in a warm place will often thin it. If, however, it does not do so, add a few drops of spirits of turpentine direct to the dope, thoroughly mixing them.
Lack Of Sufficient Tooth. If you do not use enough retouching dope the surface of the plate will be too smooth. If you work too long on one spot on the negative the film will become smooth and not take the lead. The only thing to do in such a case is to remove all the work and begin over.