The method of introducing the dye into the emulsion has considerable influence on the result ing colour sensitiveness. Those dyed in the emulsion—that is, before coating—have usually a lower x than plates bathed in a dye solution ; that is, they are less colour sensitive, though the reason for this is not apparent.
Although excellent commercial colour-sensi tive plates can be obtained, the following information may be useful. To sensitise for blue-green and green, up to about A 5,500, the best dye is acridine orange NO, of the Leonhardt Farbwerke, Miihlheim.
Stock Solution Acridine orange NO . 9.6 grs. g.
Alcohol . . . 1,000 ecs.
Industrial alcohol may be used instead of the pure. The actual sensitising bath is : Stock dye solution . 4 Oz. 200 CCS.
Distilled water to . 20 ;, 1,000 „ For greenish-yellow and yellow up to A 5,90o, erythrcsine should be used, and of most suit able dyes are bluish erythrosine of the Badische Anilin and Soda Fabrik, that made by Schu chardt, of Garlitz, or the pure dye of Meister, Lucius and Briining, of Hoechst. A stock solution is made of 1 : moo of alcohol, as with acridine ; the sensitising bath is : Stock dye solution . 4 oz. 200 ccs.
Liq. ammonia: (.88o) . 96 mins. ro „ Distilled water to . zo oz. 1,000 „ Erythrosine is an excellent sensitiser for the above region, but it leaves a minimum or gap in the bluish green, which, however, fills up with a generous exposure, so that it can be used instead of acridine orange for all but spectrum work in the blue-green, and has the advantage of being more readily washed out of the gelatine, alcohol alone being able to remove the last traces of acridine.
To sensitise for green, yellow, and red up to about A 6,200—A 6,400, one of the following should be used : orthochrome T, pinaverdol, pinachrome, or homocol, the action as red sensi tisers being greater in the last two than the first two. A 1 : moo alcoholic stock solution should be made, which should be kept in the dark ; the actual sensitiser is— Stock dye solution . zo mins. 2 ccs.
Distilled water . 20 oz. 1,000 „ For the extreme visible red pinacyanol should be used in the same way.
For the infra-red, about wave length A 7,18o, " little a," as it is usually called, dicyanine should be nsed as above, only the stock solution must be added to the water at the very last moment, when everything is quite ready, and the plate immediately flowed with the dye, as the weak solution loses its sensitising power very quickly.
The most convenient method of sensitising is by means of a grooved trough, into which, when filled with dye solution, the plates can be dropped. Or the worker may use d dish twice as large as the plates to be sensitised at one time. These are put at one end of the dish ; the dish is tilted, and the dye solution poured into the empty end ; then the dish is tilted back, so that the dye solution runs in an even wave over the plates. The dish should be gently rocked for three minutes, then the plates removed and washed in a good stream of running water for three minutes, and set up to dry in a proper drying cupboard, or in an air-tight box contain ing a saucerful of calcium chloride.
An alternative method of sensitising which considerably hastens the drying, is to replace two-fifths of the water in the above baths by acetone or methyl alcohol ; the plates then dry in about half an hour in a warm place.
The best panchromatic sensitiser is that sug gested by R. J. Wallace.
Pinacyanol (1 : s,000 sol.) 134 mins. i4 ccs.
Pinaverdol (z 1,000 sol.) so6 „ II „ Homocol (s s,000 sol.) io6 „ I I „ Liquor ammonite . . 318 „ 33 f 1 Alcohol , . •8 oz. 11 Distilled water to . 20 „ 1,000 „ The plate to be sensitised should be clean work ing and with a fine grain, and therefore not too rapid. Care must be exercised as to the dark room illumination and no light should be used for red sensitising. E. J. W.