If from a defect in the construction of the instrument, or from other causes which will be pointed out more particularly in the Second Part of this work, diffused white light gains entrance into the Camera, it produces indistinctness of the image by affecting the Iodide more or less universally.
The luminous image of the Camera not being perfectly pure, mere over-exposure of the sensitive plate will usually have the same effect. In such a case, when the developer is poured on, a faint image first appears, and is followed by a general cloudiness.
The clearness of the developed Collodion picture is much influenced by the condition of all the solutions employed, but particularly so by that of the Nitrate Bath. If this liquid be in the state termed alkaline ([p. 88]), it will be impossible to obtain a good picture; and even when neutral, care and avoidance of all disturbing causes will be required to prevent a deposition of Silver upon the shadows of the image: especially so when Nitrite of Silver or Acetate of Silver are present, both of these salts being more easily reduced than the Nitrate of Silver.
The use of Acid is the principal resource in obviating cloudiness of the image. Acids lessen the facility of reduction of the Salts of Silver by developing agents ([p. 98]), and hence when they are present the metal is deposited more slowly, and only on the parts where the action of the light has so modified the particles of Iodide as to favour the decomposition: whereas if acids be absent or present in insufficient quantity, the equilibrium of the mixture of Nitrate of Silver and reducing agent which constitutes the developer is so unstable, that any rough point or sharp edge is likely to become a centre from which the chemical action, once started, radiates to all parts of the plate.
Various acids have been employed, such as Acetic acid, Citric acid, Tartaric acid, etc. Nitric acid is the most effectual of all, but is seldom used, because, although the image can often be developed with great clearness when the Bath contains a small quantity of Nitric acid, yet such a condition is not favourable to intensity; on the other hand, films which are prone to irregular reduction, such as those prepared in a chemically neutral bath or a bath containing Acetate or Nitrite of Silver, are likely to give the greatest vigour of impression. Hence, when this quality is desired, the use of Nitric Acid will be adopted cautiously.
The state of the Collodion must be attended to as well as that of the bath; it should be either acid or neutral, not alkaline. Colourless Collodion may be used successfully as a rule, but sometimes a little free Iodine is advantageously added. Care should be taken in introducing organic substances, many of which dissolve out into the bath, and spoil it for giving clear pictures. Glycyrrhizine, however, which is recommended to produce intensity of Negatives, has no effect of that kind, and may be employed with safety.
The condition of the developing agent is a point of importance in producing clear and distinct pictures. The Acetic acid, which is advised in the formulæ, cannot be omitted or even lessened in quantity without danger. This is particularly the case in hot weather or under any other condition which favours reduction, such as neutrality of the bath, etc.; at all times, in fact, when the solutions of Pyrogallic acid and Nitrate of Silver decompose each other with unusual rapidity.
In addition to the points now mentioned, viz. the state of the Bath, of the Collodion, and of the developer, the reader should also study the remarks made in the Third Section of Chapter III. on the effect of surface conditions in modifying the deposition of vapour and of metallic Silver: he will then in all probability experience but little difficulty in dealing with those numerous irregularities in the action of the developing fluid, which often prove the greatest hindrance to the successful practice of the Collodion process.