Odd Black Stain with Gum

[Jon Harwood]

I have a new affliction with some gum prints. On a intermittent basis I am getting small black or very dark brown spots that appear when a freshly coated piece of paper dries. They are not visible immediately after coating the paper but appear during the drying process. Currently I am using Fabriano Artistico Extra White hot press paper sized with gelatin that is hardened with glutaraldehyde. Once the little spots appear they remain permanently, ruining the print in most cases. I am at a loss to explain the origin of these spots and wonder if anyone else out there has encountered this problem.

 

[Kerik]

Are these spots independent of the pigment color you're using or are they happening with black pigments?

 

[Jon Harwood]

Are these spots independent of the pigment color you're using or are they happening with black pigments?

The spots seem independent of the pigment. I have had them come up with M. Graham Indian Yellow and Daniel Smith Deep Scarlet.

I have a theory about what may be happening. I was looking around my work area thinking about the problem and I suspect it may be my Badger Brush. I have been using badger varnish brushes to remove streakiness in the emulsion coat. I observed apparent rust in the shanks of the brush with a stain running down the bristles. It appears that the maker wasn't concerned about corrosion since it is a VARNISH brush. So it might be that rust particles are working their way down the brush into the wet emulsion with a stain spreading as the drying goes on (maybe). I will try a badger shaving brush with a wood handle and see if that cures the problem.

However, I will be grateful for any enlightenment available, in case my theory is just baloney

Thanks,

jh