This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
Yellow Negatives. This is occasioned by prolonged development, by a decomposed Pyro Solution or by an insufficient quantity of or decomposed sulphite of sodium, in the developer. Sometimes the yellow merges into a red-brown, depending somewhat on the developer. This may be remedied by using a clearing solution consisting of
Pulverized Alum................1/8 oz.
Sulphuric Acid...............1 dram.
Always pour the acid into the water; never pour water into acid. The negative should remain in the clearing bath for about ten minutes and should then be well washed.
Yellow and Brown Stains. These stains are usually accompanied by an iridescence on the surface of the negative. It is caused by using too warm a developer, by strengthening developer while plate is in the tray, or by using a developer stronger in alkali than the plate will stand. Never strengthen the developer by pouring the solution directly into the tray which has a plate in it. Remove the plate, add new developer, pour it into a graduate, replace plate and flow developer over it. These stains are also sometimes caused by using a plain hypo bath which has been used too long and which has become dark in color. These stains may usually be removed by local application of a reducing solution.
Weak or Thin Negatives. This may result from several causes. The film on the negative may be too thin. If it has clear shadows it is the result of under development. If it has plenty of detail in the shadows it is a case of over exposure or too weak developer. This may be remedied by intensification.
Green Fog. The plate is covered with a green fog or film when hypo has been allowed to get into the developer.
Transparent Lines. This is sometimes found on plates after development and is caused by scratching the film by dusting with a coarse brush.
Mottled Negatives. These are caused by the precipitation from the fixing bath which contains alum, if the solution is old or dirty. Negatives cannot be remedied when in this condition but it can be guarded against by preparing a new fixing bath.
Crystallization on Negatives. This is caused by insufficient washing after fixing. If the salt is just beginning to appear and the film of the negative has not been destroyed the plate may be saved by a thorough washing for two hours followed by a bath composed of 50 grs. of Persulphate of Potash, sometimes known as Anthion, to 16 oz. of Water. They should be soaked for ten minutes, washed and examined, and this operation repeated three or four times. If the hypo crystals disappear after this but the yellow stain remains, treat with the cleaning solution. If, however, the hypo has eaten into the film you might just as well throw away the negative.
Frilling. This consists of the film separating from the glass at the edges of the plate and wrinkling up. This sometimes occurs in the development in hot weather. Remedy, keep developer cool with ice. It also occurs in the fixing bath and when washing. This occurs when using too concentrated or too old a fixing bath or washing in too warm water. Alum in the fixing bath prevents frilling.
Blisters on Negatives. The same causes that produce frilling sometimes produce blisters in the middle of the plate. Plates made in the hot summer months by manufacturers who have no ice plants in connection with their factories, for keeping down the temperature, often have minute blisters over their entire surface, and these blisters are so small as not to be perceived until after the plate is dried. As a usual thing they do not effect the printing qualities of the negatives and do not show except in the case of a clear sky. In such a case the sky can be blanked out by covering with a piece of paper and the sky of another negative printed in as described in the next chapter. Too much acid in the fixing bath will also produce blisters.
Round Transparent Spots. These are caused by bubbles in the developer. Break the bubbles with the finger as rapidly as they appear. The negative can be saved by skilful touching up, which will be explained later on.
Irregular Transparent Spots. These are caused by dust on the film of the plate before it was exposed. They can be filled in as will be described later on.
Small Dark Spots. Small dark spots sometimes appear all over the negative. This is sometimes caused by old plates that have deteriorated but more often from faulty fixing, especially where negatives are fixed in a tray and lay in a horizontal position. Small pieces of film and dirt settle on the face of the negative and particles of the bromide of silver are not fixed out on this account. Dirt also settles and imbeds itself in the film. There is no remedy. It can be avoided by fixing in a bath where plates are held in a vertical position and all dirt sinks to the bottom.
Streaks. These are sometimes caused by excess of acid in fixing bath, particularly if the streaks run the same way that the plate was inserted in bath. They sometimes occur from slight leakage of light in plate holder or bellows, but then show when plate is developed and before fixing. There is no way of saving such plates. Prepare new fixing bath or hunt up leaks in camera or holders as the case may be. Fog. Fog is a deposit of silver which has the appearance of a grey veil all over the plate. It deepens the shadows and gives the entire negative a flat, dirty appear-Iance without sharp lines. There are many causes for fog, among them being over exposure of the plate, leakage of light through a defect in the plate holder, or camera, or the admission of white light into the dark room. Fog may be produced by an unsafe lamp in the dark room, either at the time the plates are loaded or during development. A developer which is too strong in alkali will also produce fog. If the plate has been exposed to light before development the fog will make its appearance before the image does. Very old plates also have a. tendency to fog. If the fog was caused by over exposure or light leakage in camera it can be verified by examining the edges of the plate where it was held in the holder. If the protected edges remained white then the latter was the case, but if the entire surface of the plate is fogged then it is probably a case of unsafe light in the dark room. Fogged spots at one side or one corner of the plate are attributable to carelessness in inserting the slide in the plate holder after exposure, allowing the white light to creep in by inserting one corner of the slide first. As a general rule if the fog is not too dense and the contrasts are good the plate can be saved by reducing it until all signs of fog have disappeared, and then after giving it a thorough washing the plate can be intensified to the required shade. Local reduction can be used where portions only are fogged followed by local intensification. Small fog spots may sometimes be successfully removed by allowing the film to dry thoroughly and then reducing by means of the alcohol rubbing process as above described. If it is suspected that the fog is owing to leakage of light through the camera or holder careful examination must be made until the source is discovered and the fault remedied. If the dark room lamp is suspected it should be carefully tested by exposing a fresh plate to the rays of the lantern for several minutes and then developing it. If the developer produces fog and yet is not too strong in alkali then we know that the lamp is at fault and steps must be taken to procure another ruby glass or to fit an orange glass or paper over the ruby.