26 PHOTOGRAPHIC FACTS AND FORMULAS 
taken as to the use of a green safelight. These dyes sensitise 
to about 720. For the extreme red and infra-red, dicyanine 
must be used. This does not sensitise for green at all, and 
great care must be taken in protecting the dye and its solution 
from light. 
Only perfectly clean glass dishes should be used for bath- 
ing plates; old porcelain dishes and metal tanks are to be 
avoided, as, in the former case, they are apt to contaminate 
the dye baths from traces of old solutions held in the cracks, 
and metals tend to reduce the dyes and cause fog. Home- 
bathed plates will not keep well, and the sooner they are used 
the better. 
The following method of hypersensitising plates gives 
extraordinary colour sensitivity and speed, but the plates will 
not keep more than about 36 hours. Three stock solutions of 
dyes are required: 
A. Pinaverdol lg 7.68 gr. 
Alcohol, 90° 1000 ccm 16 oz. 
B. Pinachrome 0.05 g 0.384 gr. 
Alcohol, 90° 1000 ccm 16 oz. 
C. Pinacyanol 0.05 g 0.384 gr. 
Alcohol, 90° 1000 ccm 16 oz. 
D. Solution A 405 ccm 634 oz. 
Solution B 405 ccm 634 oz. 
Solution C 210 ccm 3Y4 oz. 
If absolutely correct rendering of the colours is required, the 
ratios of these solutions may have to be altered slightly. It 
will be understood also that the English dyes, sensitol green 
and sensitol red, may be used instead of the pinaverdol and 
pinacyanol with equally satisfactory results. Stock dye solu- 
tion: 
E. Stock solution D 400 ccm 60z., 192 min. 
Alcohol 600 ccm 9o0z., 288 min. 
