OK, Here's one that has me stumped. This is probably not the forum for it, but I don't really know where to ask, so here goes:
In a box of mixed photographic goodies (junk) sent to my friend for appraisal, there is a Kodak Illuminator Model 1A 10x10. It consists of a plastic housing, a 60 watt light bulb and a front frame holding a sheet of heavy blue glass over a sheet of white diffuser glass. The clips holding the glass are not spring mounted, or else I'd say it was for viewing x-rays or some other transparency, but I may be splitting hairs here.
Can anyone think of a situation where blue light would be necessary for viewing?