Many attempts have been made to secure instantaneous results on Autochrome plates but the methods employed have been uncertain in result and the procedure beyond the abilities of the average worker.
Thanks, however, to the researches of Monsieur Ch. Simmen and the skill of Monsieur F. Monpillard, a process is now available enabling workers possessing a dark-room and ordinary manipulative skill to so increase the speed of their colour plates, either Autochrome or Omnicolour, that in good light fully exposed results may be obtained with instantaneous exposures.
The means employed are : (1) Bathing the plate in a special sensitizing bath.
(2) The use of a taking screen adapted to the plate so treated.
Beyond the ordinary articles used it will be necessary to provide
Alcohol at 90o (ethyl).
A drying box and some calcium chloride.
A whirler and some blotting paper.
The drying box can easily be improvised. Take any well-made box and make it light-light, and as air-tight as possible. Arrange the interior so that the plates may be easily disposed for drying, either by leaning against the sides of the box or in a rack leaving as much space as possible between the plates. Allow room for the insertion of the box containing the calcium chloride.
Instructions. Take 3 1/2 ozs. alcohol 90o and add to it 10 1/2 ozs. of distilled water. Label " Alcohol solution 22.5°."
In ordinary practice it is preferable to sensitize two plates at a time. For two quarter-plates use a 7 X 5 dish and 3 1/2- ozs. of solution.
To 4 ozs. of the alcohol solution add 1/2 oz. of the ammonia solution B and 1/2 oz. of the sensitizing solution A as supplied.
From this onward all operations are preferably performed in complete darkness; the Virida light as used for Autochromes is,however, permissible if the illumination be very feeble and all operations carried out at the greatest distance possible from the light.
Place the first two plates in the solution and, with occasional rocking, allow them to remain immersed for 3 to 3 1/2 minutes. At the expiration of this time withdraw the plates and stand on end on some clean blotting paper to drain.
Then put two more plates in the solution, allowing them to remain in for four minutes.
If the bath be used for sensitizing more than four plates, about one-third of the quantity should be thrown away and replaced by the same quantity of fresh bath. If, after use, it is desired to keep the bath for further use, it should be stored in a well-stoppered bottle in the dark, as otherwise it will lose its colour and activity.
While the second pair of plates are immersed, the first, which have been draining, can be placed in the whirler - given a few seconds whirling, then placed in the drying box. The whirler may be dispensed with if the plates be shaken violently and all drops removed from the back of the plate, but we advise its use, as the minimum quantity of solution is retained by the plate and drying is consequently more rapid. Once all plates are stood in the drying box, the box containing the calcium chloride should be introduced, the lid removed and the drying box closed.
Time of drying will depend on the state of the calcium, the number of plates, etc., but a good plan is to sensitize at night and remove plates in the morning. The cards found in contact with the plates should be stored in a dry place in order that they may be in the best condition for again placing in contact with the plates when loading the dark slides.
Plates so sensitized will retain their speed for at least a month, after which time they will gradually become slower.
Before exposure, the glass side of the plates should be thoroughly cleaned.
Exposures may be calculated on a basis of one-fifth those necessary for a normal Autochrome.
With a focal plane shutter and a lens working at f/4'S, well-lit subjects in sunlight will be fully exposed in 1/25th of a second.
Development is carried out as usual (Quinomet being preferable to Pyro). The Virida safe light is used but should not be approached till the plate has been in the developer some 30 to 40 seconds. The plate will at first appear darker than usual owing to the colour imparted by the sensitizer, but gradually resumes its normal appearance.
All other operations are performed as usual.
Screens are supplied for use with daylight, or flash powder at the same price.