Yellow spots in printed areas

[basslaw]

I print on Hahnemule museum etching paper with carbon black ink.
I have yellow spots developing on the paper weeks/months after printing.
these appear on both the front and back of paper in the printed area. any ideas?

[IJM_TechSupport]

The paper has most likely been exposed to some form of either acid or sulfur contamination either within your printing room/studio environment, or previous to being inked.

Exposure of contaminated paper to air and printer ink can make this appear.

Expose the paper to UV light (direct sunlight for a few days) and see if the spots go away. It could very well be malformed optical brighteners that are reacting. They can be cured out by UV.

best,
Walker