Intensifier for use with under-exposed negatives, or in cases of under-development even of over-exposed negatives.
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Dissolve the mercuric chloride in warm water and allow to cool, but do not stir nor shake the container before use. The solution will keep well in a dark brown bottle.
Put the negative emulsion up into the solution and allow the silver image to bleach. The more vigorous this reaction the contrastier the resulting negative. The negative is completely bleached when it is completely white when viewed through the back.
If only the shadows are to be intensified (i.e. in cases of under-exposure) immerse the dry negative shadows to be bleached (removing it before the heavier densities are affected).
As soon as the negative is sufficiently bleached wash it for 10 minutes in running water. Any slight deposit that occurs can be removed be carefully swabbing the surface under water with a piece of cotton wool.
The negative is then blackened in a solution of 25 mililiters Ammonium hydroxide (0.910) in 1 liter of water. Finally wash for 10 minutes.
For negatives that it is desired to preserve it is better not to use ammonia, but to blacken in a 10% solution of sodium sulphite, or in an ordinary developer.