The introduction of the Autochrome plate puts it within the power of the amateur photographer to record the colour as well as the outline, light and shade of his subject, and that with very-little more trouble than in making an ordinary negative. The instructions for the use of Autochrome plates have been modified by Messrs. Lumiere since they were first issued, and a host of other formulae and instructions have been put forward by different workers. Most of these I have tried, only to come to the conclusion that the best results are most certainly and most easily obtained by following closely the directions given by the makers. What follows, therefore, is based on Messrs. Lumiere's instructions, modified only where needed to allow of the use of chemicals obtainable of any British chemist.
The complete outfit for Autochrome photography, besides the camera and other things used in ordinary photography, consists of a supply of the plates and the few chemicals, a special colour screen and a holder to fit it to the lens, some black cards which are supplied with the plates, a dish and a safe light. Messrs. Lumiere supply " Virida " papers, which may be enclosed between glasses and used in the lamp ; and the use of these " safe-lights " greatly simplifies the development of uncertain exposures.
It is best before exposing a plate to make up the various solutions required. The list is a simple one, the solutions keep very well, and although distilled water is sometimes recommended, it is not in the least necessary. The pyro (Bath A) will keep for a month at least, and the other (Bath B) keeps almost indefinitely.
*Although the makers have introduced a metol-hydrokinone developer, rendered alkaline with ammonia, formula for which is given below, I much prefer the original formula for development with pyro-ammonia, using as a preservative of the pyro solution a trace of sodium bisulphite lye. This developer does not affect the skin as the other (Quinomet) does. The developer I use invariably now is as follows : Bath A.
* Those who prefer the quinomet developer, and are not susceptible to metol poisoning, can either buy it ready prepared or mix it up from the formulae given at the end.
Sodium bisulphite lye
or Potassium metabisulphite......
Liquor ammonia 880o.............
Potassium bromide ................
For development, half an ounce of A is diluted with five ounces of water, and, immediately before use, half an ounce of B is added.
Although a light may be used for development, this is only possible from the fact that the developer seems to rob the plate of much of its colour sensitiveness. As far as filling slides and commencing development are concerned, the work should be done in total darkness. This is not difficult. All should be got ready beforehand ; the dark slides open and dusted out ; the black cards black side upwards, where the hand can be put upon them in a moment ; the box of plates with its outer paper removed ; and a clean soft piece of washleather.
Two things call for note in filling the slides. The glass side of each plate must be carefully cleaned by breathing on it and rubbing it with the washleather, and on no account must the film side be injured. A slight scratch on it will show in the finished picture as a bright green spot. The plate after cleaning has a black card put upon it, with the black side next the film, and is put into the dark slide, not forgetting that it is the glass side that must come next the shutter. The card is used to protect the film while it is in the slide. .
As the glass side faces the lens, the sensitive film is further away from the lens than when an ordinary plate is in the dark slide. In order that the picture may be sharply focussed, therefore, there must be some compensation for this. The colour screen, if placed, after focussing, between the lens and the plate, lengthens the focus of the lens sufficiently to allow for the plate being turned. Or the ground glass may be turned ground side away from the lens, which, as there is not much difference between the thickness of the glass of an Autochrome plate and of the ground glass, will serve the same purpose. The writer does not adopt either expedient, but merely racks in the back of the camera, after focussing, about the thickness of a plate.
The special yellow screen supplied by Messrs. Lumiere must be
" used, or the colours will be incorrect. If no screen at all is employed, nearly all the colours will have a violet shade. If in spite of the screen this violet tint makes its appearance, there is a leakage of light into the camera.