Yellow stains.
Due to the developer, are easily removed by Edwards' clearing solution, which we have found most effectual—
| ℞ | Sulphate of iron | ℥ iii. |
| Alum | ℥ i. | |
| Citric acid | ℥ i. | |
| Water | O i. |
Transparent spots.
Are due to dust in camera or slide, or to using the “hypo” bath too long. If the spots have sharply defined edges, they are due to air bubbles forming at the beginning of development.
Halation.
This is a bug-bear we have had little experience of, though we have taken many interiors. The only occasion on which we met with it was once when the plate was overexposed on a stained glass window, containing much blue in it. If a large stop be used, and the exposure kept as short as possible, our experience is that no halation need occur. If, however, the student fears it, and there is always a danger of it where any bright lights act on the film, he should, with a squegee and some glycerine, apply a piece of some dark tissue to the back of the plate; this is easily stripped off before development.
Defects due to damp.
All plates should be kept in a dry place, and whilst travelling it is as well to keep them in tinfoil. The effect of damp is to produce patches, which either do not develop at all or develop unequally.
Removal of varnish.