ORTHOCHROMATIC PHOTOGRAPHY 25 
generally used. The extra blueish kind should be used in a 
1:5000 aqueous solution with the addition of 0.5 per cent 
of ammonia. This gives a strong yellow, orange and green 
sensitiveness, but a marked want of sensitiveness in the blue- 
green. For this reason the new dyes mentioned above may 
be substituted with advantage, but the proportion of ammonia 
should be reduced to one-tenth. 
Green, Yellow and Orange Sensitisers—To obtain sensi- 
tiveness up to 620 to 640 in the orange, any of the following 
dyes may be used: isocol (Bayer), orthochrome T, pina- 
verdol (Hoechst), sensitol green (Ilford), or pinachrome 
(Hoechst). These should be used in about a 1: 50,000 solu- 
tion, with the addition of a little ammonia, not more than 
0.01 per cent. The plates should be bathed for 3 or 4 
minutes, then rinsed in alcohol, and dried as quickly as pos- 
sible. Instead of using ammonia in the bath, it is preferable 
to use about 0.02 per cent of borax, which does not tend to 
give so much fog. The dilute dye solutions have a tendency 
to deposit a flocculent precipitate, and this can be prevented 
by adding from 20 to 40 per cent of ethyl or methyl alcohol 
or acetone to the bath, but this method does not give such 
good colour sensitiveness as with aqueous solutions. A deep 
red safelight may be used until the plates are covered with the 
dye solution, and then the rest of the operations should be 
conducted in darkness, or a green safelight used. 
Panchromatic and Red Sensitisers—Pinacyanol (Hoechst) 
or sensitol red and sensitol violet (Ilford) may be used for 
red sensitising and panchromatic plates, the violet dyes giving 
the best all round results; though a mixture of orthochrome 
or sensitol green with the violet may be used, in the ratio of 
2 of the former to 1 of the latter. The total strength of the 
bath should not be more than 1:75,000. Ammonia or borax 
should be used in the same way and the same precautions 
