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518
History of Three-Color Photography
For use this stock solution should he diluted with three times its volume of water. The actual developer was :
Solution A 100 ccs.
Solution B, diluted 100 ccs.
Water 1000 ccs.
To compensate for errors in exposure and variations of temperature the following system was devised :
Have ready in a small graduate 45 ccs. of diluted ammonia solution B to be added wholly or partly to the bath during development, if necessary. As soon as the plate is in the dish, count the number of seconds from the moment of entering the developer until the appearance of the first outlines of the image. The sky, however, should not be taken into consideration. It is unnecessary to examine the plate until 20 seconds have elapsed, as whatever be the degree of exposure the first sign of the image will not be seen till 22 seconds have elapsed. The number of seconds before the appearance of the image is the guide to the further development of the plate, which should be carried out according to the following table :
Time of first appearance
Quantity of ammonia,
Total time
of develop
of image (not counting sky)
*%, strength, to be added after image appears
ment including time of appearance
Seconds
Ccs.
Minutes
Seconds
22 to 24
None
2
—
25 to 27
2
2
15
28 to 30
8
2
30
31 to 35
15
2
30
36 to 41
20
2
30
42 to 48
25
2
30
49 to 55
30
2
45
56 to 64
35
3
—
65 to 75
40
4
—
over 75
45
5
—
The additional quantity of B solution must be added when the outlines begin to appear.
It will be seen by the above, for example, that when the image takes 28 seconds to appear 8 ccs. of ammonia solution B should be added and development continued until the expiration of 2 minutes 30 seconds from the time the plate was placed in the developer.
Von Hubl34 strongly recommended pyrogallol as the developer, on account of its tanning action on the gelatin. P. S. Chataux35 suggested immersion of the plate first in the pyro solution and after a few seconds the addition of a little of the ammonia, continuing this addition if the plate appeared to lag, so as to complete development in 2y2 minutes. L. Cust36 considered that there was far greater possibility of correcting expo