This section is from the book "A Manual Of Photography", by Robert Hunt. Also available from Amazon: A Manual of Photography.
Having on many occasions subjected the simply nitrated photographic paper to the influence of chlorine and iodine in close wooden boxes, I was often struck with the sudden change which light produced on the wood of the box, particularly when it was of deal ; changing it in a few minutes from a pale yellow to a deep green. This curious effect frequently occurring, led me to observe the change somewhat more closely, and to pursue some experiments on the subject. These produced no very satisfactory result. They proved the change to depend much on the formation of hydrochloric and hydriodic acids, and the decomposition of water in the pores of the wood. I found well-baked wood quite insusceptible of this very curious phenomenon. The woods of a soft kind, as the deal and willow, were much sooner influenced than the harder varieties, but all the light-coloured woods appeared more or less capable of undergoing this change. All that is necessary is, to place at the bottom of an air-tight box, a vessel containing a mixture of manganese and muriatic acid, or simply some iodine, and fix the piece of wood at some distance above it. Different kinds of wood require to be more or less saturated with the chlorine or iodine, and consequently need a longer or shorter exposure. The time, therefore, necessary for the wood to remain in the atmosphere of chlorine can only be settled by direct experiment. Wood is impregnated very readily with iodine, by putting a small portion in a capsule a few inches below it. It does not appear to me at present that any practical result is likely to arise out of this peculiar property ; it is only introduced as a singular fact, which is perhaps worthy a little attention.