Lea, It is not quite clear what your friend wants to do but if you take plain enlarging photo paper and place your hand on it and keep it there while the paper is exposed to reasonably strong white light (as in making a photogram) after about 5 minutes of such a situation if you remove your hand you will see a perceptible difference between the paper that was covered and that which was not ... essentially a photogram of your hand. This shadowimage will, of course, eventually fade away. On the other hand, if you preexpose a piece of paper to some image then it can only be developed under safelight conditions if you expect the image to be visible against the fog that would be apparent if a safelight is not used or if fogging light reaches the paper. The stage can be flooded with red light during the process I guess. Making a darkroom out the theatre. Anyway, another way to deal with this is to cover the paper with red cellophane and dream up a way of spreading developer over the paper without letting white light leak under the cellophane to an appreciable extent. I am sure there are variations on the theme ... there may also be other materials that change on exposure to light - I have seen one that is used to demonstrate high speed photography in a science museum. It is a phosphorescent material that reacts quickly but where the change in brightness of the material fades away slowly - and then it can be "flashed" again. Visitors to the exhibit jump between a flash and the screen and leave a temporary shadowgram of their "flying" bodies impressed on the screen. Andy > A friend is looking to use either photo paper of photo film in a performance art piece he is doing and he wants something with an exposure time of about 5 minutes...meaning a change will take place and be seeable by th audience in that much time.
