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.
Frilling. Caused by warm solutions, warm hypo, or warm wash waters. Remedy: Keep all solutions and wash waters cool. (See paragraph 57.) Dry your negatives in a cool, well ventilated room so that they will dry as quickly as possible. Dry the negatives at an open window, being careful that the sun does not strike the same. Dry with electric fan when possible.
Uneven Development. Caused by not covering the entire plate when first pouring on the developer. Parts of the plate that do not come in contact with the developer will develop slower, and no matter how long you develop it will show uneven developing. Insufficient amount of solution will also cause uneven development.
Blisters. Caused by warm wash waters, warm developer, warm hypo and washing too long. Remedy: Keep your solutions and wash waters cool, and do not wash longer than one-half hour in running water. You must also be careful and see that your carbonate of soda is not too strong. If stronger than the formula calls for, the film will soften very readily and you are apt to obtain blisters.
Pin Holes And Spots. These are produced in so many different ways that it is impossible to enumerate and describe all of them. The best way to prevent them is to observe cleanliness in all operations. Your dark room, graduates, measures and trays which contain developing solutions should be kept clean. Your camera and plate holder dusted occasionally. The fixing solution should be filtered to free it from any sediment, and each plate must be carefully dusted before placing in the holder and before placing in the developer. The most common spots are small, round, or nearly transparent, with dark defined edges. These are caused by air-bubbles adhering to the surface of the plate when the developing solution is first flowed over it. The gelatine being hard and the bubbles preventing the alkalies from taking hold of the emulsion at once, is apt to leave these little air-bells. These bubbles can be removed by gently passing a tuft of absorbent cotton, thoroughly saturated with developer, over the surface of the plate immediately after it is immersed in the developer.
WOODLAND MIST Study No. 2, See Page 343 Wm, T. Knox, New York City
Round Transparent Spots. May be caused by a drop of bromide solution, or a drop of hypo solution falling on the plate either before the developer is flowed over or even during development. Remedy : Never add bromide to the developer while the plate is in the tray; either remove the plate from the tray and then add the bromide (mixing well), or pour your developer into a graduate and add the few drops of bromide in the graduate and then pour the developer back over the plate. Wash the hands carefully after being in hypo, thus avoid carrying any of the solution into the developer.