Filter weird - ice crystals "new coating"

Hello,

I have Schuller 1.25" photometry filters.
I left them at their original plastic cups for 4 months in a drawer.
When I opened and look at the filters- they had a strange cover of a whitish material that looks like big ice crystals on a windowpane.
It is very hard and can not be cleaned.
The filters are currently useless!.
What can be the couse of this strange phenemenon?
How can it be cleaned of, without damaging the optic surface itself?

Kind regards,
Ido.

It sounds like it may be a fungus. If so it may have etched the coating. Is there a chance it was put away damp? I'd try to clean them with regular optic cleaning methods. Just don't rub it.

Good luck - Cal

Hi Ido -

I don't have experience with Schuller filters but their coating process may have something to do with the patterns you see. I'd try to contact Schuller. Good luck with it.

Bob Polcyn