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.
Wrist And Forearm Become Tired. It is advisable to have a cushion under the elbow, which will raise your arm to exactly the right position for work. If this is not done the forearm, and even the shoulder, will soon become tired. Both the elbow and wrist should rest in such a way that you may work indefinitely without their becoming at all tired. Cultivate working in the easiest position possible, always sitting erect. This might at first appear awkward to you, but if you do not work in this way you will soon become tired, and the hand is apt to become unsteady. There is no need of your being nervous if you use judgment and follow the instruction. It is advisable, especially for your first experiments, to work only a half-hour at a time and then to rest, walking around for a few minutes. Forget your work for the time being, and when you again take it up you will feel somewhat refreshed and not at all tired.
Finger Marks On Negative. The negative should always be covered with the mask, as this will protect it from finger marks. The mask may be made of black or any dark paper; a hole two or three inches in diameter should be cut in the center of an 8 x 10 piece of paper. The mask may be held in position by tacking the upper edge to the desk.
Cannot Remove Blemishes. When working on freckles and extremely transparent portions of a negative, some difficulty may be experienced in building up the transparent spots sufficiently. This may be due to one of two reasons: (a) You are working with too hard a lead. (b) You are working too lightly and glaze over the surface before a sufficient quantity of lead has been deposited. The remedies for these difficulties are: (a) Use a softer pencil; (6) apply the lead heavier.
Imperfection Becomes Too Black. This is due to either using too soft a pencil or working too heavily. The remedy is obvious. Build up the imperfection until it just matches the surrounding tint. Remember, that the blemish is not to be filled in solid, but it should be broken up with strokes that will leave a slight grain effect. When the imperfection is simply a pin-hole in size, one little touch with the point of the pencil may remove it. A stroke conforming in shape to a comma is very effective in removing both large and small blemishes.
Removing Retouching Medium. If too much lead has been applied to the negative, if you have worked on portions that should not have been touched, or if for any reason it is desired to remove the work and begin anew, apply a few drops of the regular retouching dope and with a tuft of cotton or Canton flannel cloth rub over the surface. This will eliminate all the work done and will also again provide the plate with a tooth upon which the lead may be applied. If retouching varnish has been employed instead of the dope, gasoline is the best substitute to use in order to remove the retouching. The cotton should be moistened, but not saturated with the turpentine or gasoline, yet you must use enough of either one or the other to wet up the retouching medium and remove it. Continue rubbing and wiping with the cotton until the medium has been completely removed, then rub dry with clean cotton, after which the plate may again be varnished, or, if desired, dope may be substituted for the varnish.