Want of success may arise from vapors of iodine or bromine in the camera box, mercury bath, or even in the buffs. It is incredible how small a quantity of these vapors will affect the effect of light when coming in contact with the plate, after or during the exposure in the camera. It is therefore necessary to be cautious not to mix chemicals, nor open your boxes or bottles in your room, but take them out to do it. Never hurry the operation through from lack of confidence in the result. The fact of anything being out of order, forms no excuse for slighting the process. If unsuccessful, do not pursue the same course every trial, but vary with a view to detect the cause of the difficulty.
In case of a long series of failures, institute a regular course of investigation, after this manner, commencing where the trouble is most likely to occur:
2. Is the iodine dry? If the impressions come out blue, you may rest assured it is not. Take out the iodine, wipe and dry the box, and dry the calcium.
3. Is the quick battery of the right strength? If dry, it must change the plate in from six to fifteen seconds. If any of the chloride of iodine class, it may vary from five seconds to a minute. Begin by coating light, and increase on each trial, observing the effect. If the light side of the picture seems loth to come out, and shows no contrast with the dark side, it is to be inferred that your battery is too strong, and must be reduced with water or set out in the open air for a few minutes, with the lid off. If working an old battery, never renew very strong, or it will work dark and heavy. A battery, to work well, should be gradually losing strength, but never gaining. An old battery, however, may be quickened up and made to work well for some time, by adding five of six drops of sulphuric acid, repeating the quantity as often as necessary, providing always that acid be not used in manufacturing the quick.
4. Have the plates lost their sensitiveness by being many times exposed to mercury? Clean and burn them; but if French plates, burn light, or you spoil them.
5. Are the buff s dry and clean? Examine the plate critically after buffing to detect any appearance of scum or film on the surface. If so, the longer you buff the more it shows. Scrape and dry the buffs thoroughly.