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.
Judging When A Plate Is Fixed. A plate is not "fixed" until the white, milky appearance disappears from the back and the plate has remained in the hypo bath as long again as it has taken to remove the white effect. Under proper condition, a plate should remain in a correctly prepared bath for at least fifteen minutes, or even an hour will do no harm. But if left in an old bath, at a moderately high temperature, too long, the image on the negative will be reduced.
Edges Of Negative Fogged. If, after development, the extreme edges of the negative are dark and fogged, the plates are old. Buy only plates that are guaranteed to be fresh, and use the best brands only. The slight additional cost is made up in the saving of wasted material and in securing satisfactory results.
End Or Corner Of Negative Fogged. If dark, angular streaks cross the negative from the end, the slide of the holder was not removed or not inserted properly. (See paragraph No. 93, also, Illustrations No. 11 and No. 12.) Should fog appear at the corners of the negative the trouble is with the box containing the plates. If carelessly handled the corners of the box will break open enough to admit a little white light, resulting in fog and light streaks across the corner of the developed negative.
Large Light Spots And Streaks On Negative. These are caused by one of two things: either the plate was not evenly covered with the developer when it was first poured on, or the plate was placed in the tray face (film side) down. The parts of the plate that do not come in contact with the developer when first poured on will not develop up as strong as the balance of the negative, no matter how long you leave the plate in the solution - uneven development is sure to show. Insufficient amount of solution will also cause uneven development. (See paragraph 131, and Illustration No. 23.)
Large Black Spot In Center Of Plate. Pointing the lens of the camera toward the sun will, in most cases, cause reflection, resulting in a bright spot in the center of the ground-glass and producing a black spot on the center of the negative. The higher types of lenses will not produce this spot to any great extent. When it does occur it is due to a defect in the lens, termed "flare." For beginners it is always best to follow the rule, "Never point the camera toward the sun," no matter what kind of a lens you are using.
Back Of Negative White When Removed From Fixing Bath. Plate was removed from the fixing bath too soon, not being allowed enough time for the removal of the unacted-upon silver salts. The milky appearance must be entirely removed. For proper fixing, however, the negative should remain in the hypo bath just twice as long as is necessary for the white appearance to disappear. Thus, if the white effect is entirely removed in ten minutes the negative should remain in the fixing bath for twenty minutes.