RETOUCHING, CHEMICAL (Fr., Retouche chimique ; Ger., Chemische Retouchier) Modifying or removing portions of a photo graph, usually in the negative, by means of chemical solutions applied with a brush. Thus in developing, any details that come up too rapidly may be kept back by draining the nega tive and painting the parts with a 5 per cent. solution of potassium bromide, afterwards return ing the plate to the dish and completing the development. To reduce harsh lights or dense portions, or to introduce clouds or shadows in a finished negative, a solution of ammonium persulphate (to to zo grs. tot oz. of water) may be employed, placing the negative after reduc tion in a 5 per cent. solution of sodium sulphite for a few minutes before washing. An alterna tive is to use Farmer's ferricyanide and hypo reducer (see "Redwing Negatives, etc."). To obtain a local increase of density, to insert high lights, to strengthen thin portions, etc., a solution of mercuric chloride or other intensifier may be used. The negative, after washing, is pressed
with blotting-paper to remove the excess of moisture, and is supported on a retouching desk, as nearly horizontal as possible ; the solutions, which should not be too strong, are applied quickly with a brush, and the negative washed directly the desired result is obtained.
Negatives are also improved by the use of dyes, etc. Stain matt varnish with aniline dye, red, green, or yellow being suitable. Flow the varnish over the glass side of the negative. Place the negative in a frame film (not varnish) side outwards, and expose to strong sunlight for some days or until the dye has partially faded, when the negative will give brighter and better prints. This is really a dye process of intensifica tion. The light going through the outward film to the dye beneath naturally causes it to fade, the amount of fading being governed by the density of the image.