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270 History of Three-Color Photography
the other (empty) end, then the dish is tilted back; so that the solution sweeps over the plates in one even flow free from air-bells. The dish should be now gently rocked for 3 minutes, then the plates removed, washed in a good stream of running water for at least another 3 minutes. Their sensitiveness and keeping quality will probably be somewhat greater if they are washed for 10 minutes, but they will remain good for months, after 3 minutes thorough washing. The water tap should be fitted with one of the small anti-splash filters, the fine wire gauze in which retains any solid particles that may be in the water. After washing, the plate should be well swabbed with a wad of absorbent cotton, and then placed in a drying cupboard. The quicker the drying takes place the better, so that if a current of warm, filtered air, free from fumes, can be sent through the cupboard it is an advantage, though the absence of this need not deter anyone from sensitizing plates. Drying can be hastened by placing a dish of dry calcium chloride at the top of the cupboard.
One most important point is that the room in which sensitizing is carried out, should not have been used for development and fixing. It is impossible to obtain clean results, for any air current will carry traces of developers and fixing bath on to the damp gelatin with disastrous results. This is of paramount importance.
P. E. Dhein107 stated that for spectrographic work, he was able to obtain far more red-sensitive plates by the use of the following than commercial plates; but that after keeping two days they were no better than Wratten & Wainwright commercial plates:
Pinaverdol, 1 : 2000 ale 8.8 ccs.
Homocol, 1 : 1000 ale 8.8 ccs.
Dicyanin, 1 : 1000 ale 12.6 ccs.
Pinacyanol, 1 : 1000 ale 11.35 ccs.
Ammonia 21.0 ccs.
Alcohol 400 ccs.
Water to 1000 ccs.
E. Stenger108 recommended a mixture of pinaverdol and dicyanin as giving a color-sensitiveness, similar to the luminosity curve of the eye, and suggested the name "ophthalmochromatic" for the plates. Later109 he gave the following, which is without the familar gap in the green :
Pinachrom violet 10 ccs.
Pinaverdol 10 ccs.
Alcohol 333 ccs.
Water to 1000 ccs.
The dyes were used in stock solutions 1 : 1000. Cleanworking plates should be bathed for 3 minutes in the dark and dried without washing. The sensitiveness extended to 7000 with very little damping in the minimum.
P. Richard and M. Abribat110 pointed out that solutions of the isocyanins have very little penetrative power as regards gelatin and that neutral