I have been collecting little accessories for use in an Argus C3 and just recently purchased a Walz 85c warming filter which I have considered using for special daylight effect use in the morning or late afternoon.

I have a concern about it though.

When looking through it with the naked eye it looks fine, but when examining it at a particular reflective angle with a rather powerful eyeloop (10x and 20x on opposite ends) it shows some crackling of the filter material.

Could this be a lens fungus?

If so, how might I treat it or should I just not use it?

Or is it just the age and manner of manufacture of the filter?

All my other Walz filters are in fairly good shape and do not show any significant amount of deterioration.

I really do not want to spend the extra money on Leica Elmar filters if I could find the ones I want, which are probably a better quality in manufacture.

I am reluctant to use this particular filter, because of the risk of a lens fungus infection that could spread to my best Argus C3 which has been fully refurbished to factory conditions.

Any corrective advice or information on this concern would be appreciated.

Thank you for taking the time to read this.