8. Stains on the upper part of the plate, from using a dirty slide.—To avoid these, place, if necessary, strips of blotting-paper between the supports and the glass.
9. Wavy marks at the lower parts of the plate.—a. If the Collodion is becoming thick and glutinous from constant use, dilute it with a little Ether containing an eighth part of Alcohol.—b. From reversing the direction of the plate after its removal from the Bath, so that the Nitrate of Silver flows back again over the surface and causes a stain on the application of Pyrogallic Acid.—c. Impurities on the woodwork of the frame ascending the film by capillary attraction. This is a frequent source of stains.
10. Marks from the developer not running up to the edge of the film ([p. 212]). Remedy this as far as possible by allowing the Collodion to set a little more firmly before dipping the plate in the Bath.
IMPERFECTIONS IN COLLODION NEGATIVES.
1. A want of Intensity.—a. From the development not having been sufficiently pushed ([p. 224]).—b. From the Collodion film being too blue and transparent for Negatives.—c. The Collodion newly made from pure materials ([p. 114]).—d. The plate kept too long between exciting and development ([p. 100]).—e. The Bath newly prepared from commercial crystallized Nitrate of Silver ([p. 101]).—f. The light too feeble, as on very dark wintry days, or in copying interiors, etc.
2. Inferior half-tones, with great intensity of the high Lights.—a. From the plate being insufficiently exposed.—b. The Collodion of inferior quality, either too strongly tinted with Iodine or made from impure materials.—c. The Nitrate Bath old and partially decomposed.—d. The light reflected too strongly from the object. When the light is unusually bright, a feeble Collodion and a newly mixed Nitrate Bath will be found to give better definition in the high lights than an intense Collodion, which may produce chalky Negatives.
3. The image pale and misty.—The plate is over-exposed (if so, the image will probably be a reddish-brown colour by transmitted light), or there is diffused light in the Camera or developing room. The presence of Bromides or Chlorides in the Collodion may occasionally produce the same effect.
4. The high lights of the image are solarized.—A change of colour to a light brown or red tint by transmitted light, with a dark shade by reflected light, is favoured by over-exposure of the plate, by organic decomposition of the Collodion, and by Acetate of Silver and other organic bodies in the Bath.
5. The image dissolves off on applying the Cyanide of Potassium.—The Collodion is probably over-iodized. The same thing may also happen in the Honey preservative process, when the plates have been long kept and the indurated layer of syrup not properly removed before applying the developer.
6. The developer does not run up to the edge of the film.—This is likely to occur when using Collodion nearly anhydrous; and particularly so with a new Bath not containing much Alcohol. The film will be less repellent, if a longer time be allowed before dipping in the Bath.