TREATMENT OF UNDER- AND EXPOSED PRINTS.
No amount of doctoring of a print after exposure, at any stage of its production, can equal one which has been exposed for the correct time. By the use of an actino meter, and profiting by experience, the proportion of failures should be small ; but a necessity for the employment of modified development is bound to arise occasionally. If the print is under-ex posed, the developer may be warmed ; or, if used warm already, its temperature may be increased. If, on the other hand, the print is over-exposed, the temperature may be lowered. Under- and over-ex posure result in increased and decreased contrast respectively, so that the methods suggested under the heading " Control of Contrast " (p. 210) may be employed. It must be borne in mind, however, that there is a continuing action of light liable to go on similar to that in the carbon process, hut in a modified degree. Allowance must he made for this if prints are to be kept for any length of time before development.
How TO DEAL WITH OLD PAPER.
Generally speaking, old paper which has been allowed to get damp is best thrown away, but in certain cases it may be used. The best plan is to dry it thoroughly in the oven, and then add to the developer a little potassium hypoehlorite or sodium hypohromide. The exact quantities of either of these will depend upon the co D dition of the paper, and must be found by experiment. It has also been sugges ted to print the paper right out, and merely fix the image ; but this, although prac ticable, cannot be recommended, as the results are exceedingly granular and the gradations bad. The effect of keeping paper is to flatten or fog the image when printed, and there are other methods which may be employed to overcome this, or by which the contrasts and gradations may be controlled.