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.
Lead Scratching. (a) Sometimes there are impurities or hard places in the lead which cause scratches. If these occur you may remove them by rotating the pencil on the piece of emery paper until the hard spot is removed. (6) The pencil may be too hard. It is very seldom advisable to use one harder than HHH, and for those who have a light touch even this pencil will be too hard and at times will scratch. An HH or even an H lead may be used very successfully, (c) The dope may not have been applied properly, or, if retouching varnish were used, it may not have properly dried. In either case you should be sure that the medium is properly mixed, rightly applied to the negative, and allowed to dry before you attempt to do any penciling, (d) Negative damp when medium was applied. The negative must be absolutely dry before applying either retouching dope or varnish. If it is not thoroughly dry the gelatin emulsion will be somewhat soft and the lead will not adhere, and frequently will dig into the emulsion, even though the negative be properly coated with the medium. (e) Should the negative become too warm - i. e., if you should work in too warm a room - the medium, unless well rubbed into the film, is liable to be left too gummy - tacky - and the pencil will dig into the medium rather than deposit the lead upon the negative.
Eyes Becoming Tired. (a) The beginner will usually strain his eyes in a vain effort to see the various imperfections. This is not at all necessary. In fact, its practice is to be discouraged. Sit back in your chair and proceed to work in an easy manner. Do not try to see too much or to remove too much at the very first. Take your time and proceed in a systematic manner, removing one imperfection before attempting to work on another. (b) The eyes will become tired and in time may give you
trouble, if you do not exclude all light from the film side of the negative. You should provide an opaque cloth thrown over the retouching desk and head, so as to exclude all light from the negative which would cast reflections into the eyes. The only light visible should be that which comes through the opening in the retouching desk.
Position At Desk Tiresome. Do not have your chair too far away from your retouching desk, as this will necessitate your leaning forward, and this position soon becomes tiresome. Have the chair close enough to the desk to permit of your leaning against the back. Then, sitting at almost arm's length from the negative, you will be able to work for almost any length of time without becoming at all fatigued.
Fingers And Hand Become Cramped. The pencil should be held loosely in the hand, and you should proceed to work in a free and easy manner. If you hold the pencil too tightly, the hand will soon become cramped and you will not have a free movement of the pencil.