Color Photography - Dye Mordanting
( Originally Published 1938 )
IN addition to making colored transparencies by the I gelatin Wash-Off Relief processes, it is possible to mordant or chemically prepare the emulsion of the positive so that it will absorb and retain the color of the dye more or less according to the amount of silver deposit of the transparency.
For the positive use a thin base, nitrate base film without any gelatin backing. Expose well and develop one and a half to two minutes in Eastman D-72 or D-73 developer on the thin side for other color with potassium content. (about one to four proportion) slightly of the same quality as described herein processes. For fixing use a hypo bath alum hardener low in sulphite of soda content.
THE MORDANT.—First make up stock solution as follows:
A. Water 32 OZ. 900 ccm
For use mix as follows:
Stock solution A 7 1/2 OZ. 222 ccm
Bleach the positives in this solution until a delicate copper color, then wash three minutes in running water.
DYEING.—The next operation is the dyeing. Prepare the following solutions:
Pyronine G (Natl. aniline) 14 gr. (1g) to 12 oz. (340 ccm) of water. Mix the dye print first in a small portion of warm water, then add cold water to make up the full quantity. Then add 20 min. (I% ccm) glacial acetic acid.
Thioflavin T (Dupont) 24 gr. (1.5 g) to 12 oz. (340 ccm) of water. Use warm water to start same as with the red. Add 20 min. (1 1/2 ccm) glacial acetic acid.
Methylene blue HGG (Badische) 24 gr. (1.5 g) to 12 oz. (340 ccm) water. Dissolve same as above and add the same quantity of glacial acetic acid—20 min. (I/ ccm).
Filter each color as mixed rapidly through a small cotton pad in a funnel. The washed positives are dyed in their complementary dyes. This should not exceed five minutes. After dyeing, wash in cold water until highlights are clear. The colors at this stage are dull and must be fixed or cleared to give the proper brilliancy. This is accomplished by fixing in the following:
Water 32 oz, 900 ccm
Fix a few minutes until clear and brilliant, then wash three or four minutes in cold water.
Each positive can be left in cold water until all three are ready for comparison before drying.
On account of difficulty in obtaining a correct blue dye, some users prefer to tone the blue image instead of dyeing. Positives for toning should be thinner than for dyeing.
Water 18 oz. 500 ccm
(Always add acid to liquid, stirring slowly)
Tone in the above, and fix in plain hypo the same as given above for fixing the dye images and wash several minutes and dry.
To reduce blue-toned image treat with a weak solution of ammonia water, or carbonate of soda. This turns the blue image purple. A bath of plain hypo or weak acetic acid will bring it back to the original blue. Wash again and dry.
To reduce the red use a solution of soda bisulphite 80 gr. (5 g) and water 16 oz. (450 ccm). Rewash after reducing.
Though no specific reducer is available for the yellow, bathing in a solution of hypo usually helps.
A suggestion for routine work is to make the yellow and red first. Leave these to soak in cold water. Then make several test strips of the blue at different densities and tone them. Check these strips against the yellow and red combined and make final blue of the density best suited.
Registering and binding is carried on in the usual manner, as described for Belcolor.
If you have trouble washing the dye from the high-lights or white parts of the positive, check carefully to be sure you are not fogging the highlights in expo-sure or development, causing a silver deposit which picks up the dye.