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 of hydrogen, rapidly reduces a print, by decomposing a portion of the insoluble chromo-gelatine compound, and restoring it to its original condition of solubility. The action is, however, too energetic to be of much practical use in the reduction of over-printed pictures. Protracted immersion in hot water is the best remedy.

—An under-exposed print develops rapidly, the lighter half-tones rapidly disappearing. When this tendency is seen, quickly removing the print to cold water will arrest the progress of development, and by skilful manipulation and attention, and the after use of almost cold water (say under 80°), a brilliant print may be secured.

—When a feeble print is obtained from a good negative, it may arise either from the use of a tissue containing too small a proportion of color, or from the tissue being old and partially decomposed by slow drying. If the negative be weak, the use of a tissue containing a large proportion of color will yield a vigorous image. Increased vigor may be obtained from an ordinary sample of tissue, by sensitizing it on the paper side of the tissue only, instead of immersing the whole. Printing in direct sunshine aids in obtaining a vigorous print.

—This may arise from the use of an unsuitable negative, or from the injudicious use of too hot water on a lightly exposed print, or from the use of tissue containing an excessive proportion of color, especially in conjunction with under-exposure. Sensitizing the tissue on the prepared side will tend to produce softness, even with a dense negative.