Really old russian filters

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?

Hello and welcome to Apug. If there is mold growing inside feeding on the gel layer I would put them aside and buy a new set of contrast filters. The newest filters are most likely optimized for use with modern papers.

If you cannot afford a new set, leave them out in the sun for a long while, UV should kill the mold.
You would have to experiment with the strength of the filters, but it doesn't really matter if you know if you are at grade 3 or whatever; what is important that you get the effect you want.

Those filters sound like colour printing filters. They aren't totally unsuitable for variable contrast black and white paper, but they aren't ideal.

Thanks for the quick replies.
Indeed they look like color printing filters. I decided they are too much of a risk to keep around (I don't want that kind of mold near my negatives or lenses). Keeping them in the sun may have damaged the pigments along with the mold.
I will buy a set of filters designed for B/W paper and I have put thees in warm water to separate the glass sheets and remove the gelatin. I will use them to make glass/plastic gel/glass sandwich filters or whatever else strikes my fancy in the future. Until then, I will have 66 square sheets of thin optical glass.

Thanks!