My thoughts on wet cleaning an historic textile is that it is irreversible and that it can be a very tricky endeavor. Are there stains that are distracting from the image or does it just appear "grubby." If it is the latter, it might be best to give the t-shirt a light surface cleaning with a vacuum on low suction and display as-is or store in acid-free tissue/box. If it is the former, I suggest you consult a Textile Conservator to help you navigate next steps. Even though they are t-shirts, which seem like they should be easy to wash, their age, past life, manufacturing process and materials, not to mention the type of stain, will all have an effect on how the textile will behave during treatment.
You can find someone in your area via AIC's "Find a Conservator": Find a Conservator
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Beth Szuhay
Head of Textile Conservation
Fine Arts Museums of San Francisco
de Young \ Legion of Honor
50 Hagiwara Tea Garden Drive
San Francisco, CA 94118
415 750 7611
bszuhay@famsf.orgwww.famsf.org------------------------------