All the photographs in this exhibition have been produced from either autochromes or Paget colour plates. Both these colour systems were developed during the period of intense photographic research undertaken around 1900. The theory behind both systems is essentially the same.
How do colour screen plates work?
A colour screen plate is used to record the colour information in a photograph using a black-and-white glass plate negative. The screen plates are made up of a series of very small filters, based on the colours red, green and blue. The screen plate is held against the negative in such a way that light entering the camera lens must pass through the screen plate before exposing the negative behind it.
To see how the process works, imagine you want to photograph a red apple with a green leaf, tied with a blue ribbon. The red light coming from the apple’s surface is recorded on the negative after passing through the red (but not the blue or green) filter. Similarly, the other two filters let either the green of the leaf or the blue of the ribbon through.
The negative is then separated from the screen plate and developed, and a glass contact positive plate made from this negative. The screen plate is placed against this positive plate; when these plates are correctly aligned, and viewed with a light source behind them, a colour image is displayed.
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