Thread: My Rubber Has Black Spots

Some six months ago, I mixed a batch of brown shellac in a glass jar that I keep in a cupboard and transfer some of it in a plastic sauce bottle that I use to charge my rubber which I keep in a screw top glass jar. I recently made a new rubber and after about two weeks, I noticed some black spots developing on it, almost like a very fine mold.

Does this suggest that my batch of shellac is contaminated or is it to do with the material I am using to make the rubber? The rubber is made of cheese cloth wrapped up in an old piece of T-shirt material.

Suggestions and advice will be gratefully received.

Yvan