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.
Prints Yellowing During Washing. This is sometimes caused by vegetable matter in the water. To test the water for vegetable matter, take a pail and fill it with water, placing a handful of alum in it and stirring well. Allow this to stand for a few days and pour off the water. If there is vegetable matter in the water, a slimy, mossylike substance will be found at the bottom of the pail. As a rule, water like this will not cause prints to yellow, as they are not permitted to soak long enough to bring about that result. If prints soak in the water over night and the water becomes warm, it is apt to cause them to become yellow. Wash prints as rapidly as possible, see that the wash waters are not warm, and you will have no trouble with prints yellowing during washing.
Prints Developing Irregular, Freaky And In Streaks. This generally occurs when the printing is too dark. By the time the highlights are developed and have sufficient detail, the shadows are only about half developed and appear streaky. To overcome, decrease length of printing. Occasionally, you will find in paper of all makes some that will develop streaky. To overcome this wet the print before developing.
Prints Stained Around The Edges. This occurs in old paper, and also where insufficient bromide has been used.
Parts Of The Print Will Not Develop, Leaving White Spots - Spots Blending At The Edge Like A Vignette. This is either caused by damp fingers or a splash of water. A print of this kind cannot be saved. You must guard against having anything damp come in contact with the paper, before printing, or developing.
Black Spots. Black spots are sometimes produced by rust in the water, or in the developer. Any metallic substance that comes in contact with a print, during developing, will cause a black spot.
Small Yellow Or Purple Stains. Caused by air-bells on the prints during fixing. Purple stains are generally caused by prints coming in contact with the bottom of the tray during development. Warm fingers are also the cause of purple stains.
White Spots. Small white spots, generally perfectly round in shape, are caused by air-bells gathering on the print when first placed in the developer. These should be broken at once. If this is overlooked, the spot will not develop, and even after the air-bell is brushed from the print, if allowed to remain any length of time, the developer will have no effect on the spot which was covered by the air-bell. When placing print in the developer slide it underneath the developer, and with the tip of the finger immediately remove any air-bell, or particle of dirt, which may gather on it.