Hi everyone! I've lurked around for a while but now I have a question. I just got a box of 75x75mm vintage russian filters. And by vintage I mean at least 25 yers old. They are made of two thin sheets of glass and a layer of colored gelatin in between (I took one apart to see if it's really gelatin). The markings on the go from 5cc to 99cc in magenta, blue and yellow. I would like to use them with my enlarger for variable contrast paper, but they have mould inside them. Is it ok to use them above the negative? I am using a Krokus condenser enlarger of the same vintage. And a second question is where could I buy polyester with the same properties to replace the gelatin in the filters?