For transfer of the image to paper, use is made of either the special dyes sold as Pinatype 2 or of the dyes given below, both being perfectly suitable also for positives which are not intended for transfer to paper.
Red : Dilute 25 to 35 gr_ (3 to 4 grm.) of natural carmine with a very little distilled water, add just enough ammonia to dissolve 20 to so minims (2 to 5 c.c.)---and acid distilled water to make 20 OZ. (1,000 c.c.) 3 per cent solution of pure diamine blue or benzoine blue BB.
Green: 3 per cent solution of naphthol green B. Yellow : 3 per cent solution of Thiotlavin S., acidi fied by a little citric acid.
After impregnation of the dye (about io minutes the first time) the plate is briefly rinsed, and a small squeegee then used to apply to it a sheet of sized paper (soft gelatine, with no alum, or very little), e.g. paper, as used in the carbon process (§ 660), which has previously been soaked in cold water. This is covered with moistened blotting-paper, then with rubber sheeting to prevent drying, and is then left for 10 to 15 minutes, during which time the colour passes from the hard to the soft gelatine.' From time to time a corner of the paper may be lifted for examination, taking care to replace the two gelatine surfaces immediately in contact.
For further prints, the impregnation of the plate will only need three minutes.
Whichever method is used to obtain pictures, i.e. direct dyeing of the positive transparency or transfer to sized paper, the dye must be fixed 011 the gelatine by immersion for about five minutes in the mordanting bath— Chrome alum . . IS gr. (-2 grm.) Copper sulphate gr, (2 grin.) Water, to make . 2 OZ. (100 c.c.) and then rinsed for about five minutes.
676. Dyeing of Gelatine Reliefs. To obtain reliefs for suitable material is gelatino bromide (celluloid) film without gelatine coating on the non-emulsion side. This is sensitized with bichromate, exposed under a negative through the back (the uncoated side of the film against the emulsion side of the negative), developed in warm water, the silver bromide removed in a fixing bath, and dried. The relief so obtained may be dyed by immersion in solu tions of a very large number of acid dyes.
For the preparation of a " carbon " paper readily permitting of the superposition of several component images, the process described in 1901 by A. and L. Lumiere may be used.
A glass is polished with talc powder, and the edges then coated, with a brush, by a thin solution of caoutchouc in crystallizable benzine. When the rubber is dry, the glass is coated with enamel collodion (see § 655, footnote), and, after drying the collodion, a sheet of clean paper is applied to the coated side by means of a solution of gelatine, warmed to F., into which the paper and the glass are placed. The two are brought into contact in this solution, and the excess is immediately expelled with a squeegee.
After drying, the paper is coated with white varnish, diluted with an equal volume of alcohol, and left for about 12 hours to dry. The paper, still secured to the glass, is now ready to receive the bichromate mixture, temporarily tinted with cochineal— Gelatine, emulsion . 1,000 gr. (520 grm.) Pale strong glue . i,000 gr. (520 grin.) Ammonium bichromate 525 gr. (60 grin.) Potassium citrate . . 90 gr. (so grin.) Cochineal red , . . 9 gr. (I grin.) Alcohol . . . . 4 oz. (200 c.c.) Water . . 20 02. (r,000 c.c.) This mixture, filtered through muslin, is coated on the levelled plates, in the proportion of 13 to 16 dr. per sq. ft. When the gelatine has set, the glasses are placed on racks, and dried in the dark in a current of air. The drying conditions must remain perfectly constant, any variation being liable to produce coloured areas in the final picture. After drying, the papers are removed from the glasses that have served as supports.
Following exposure under a negative (con trolled by an actinometer), the paper is trans ferred to a collodionized glass, prepared accord ing to the formula above, and then covered all over with a very dilute solution of rubber (about 6o gr. per 20 oz., 7 grm. per i,000 c.c.).
Before development, the transfer is left in cold water for about two hours to allow the gelatine to swell uniformly ; the development is carried out at between 95° F. to 104° F. when the develop ment is finished the picture is decolorized, and then presents the appearance simply of a very slight relief. It is then washed in cold water, and put aside to dry.