Dear Donia,
How can I remove or reduce foxing and mold from watercolor paintings?
Q. Dear Donia,
A. Dear James,
It is possible to reduce foxing and reduce mold staining (results will vary) on watercolors but there is no way to do it if you are not a trained conservator as the process will take a lot of testing and careful treatment.
You are lucky to be located in Stamford, Connecticut which is an area that has a lot of very capable paper conservators. To find a good fit for you, you can start at the American Institute for Conservation's Find a Conservator page. Fill out the information in the Search Criteria boxes and you'll be given a selection of conservators in your area who can assist you with this project. Be sure to look for those that specialize in Art on Paper and make sure you speak to at least three people to find the right fit for you and your watercolor.
I hopes this helps you make a decision on how to proceed. If you have any more questions, please don't hesitate to ask "Dear Donia" again.