David;
I remember a similar situation way back in 1973. We had a Restaurant that had about 40 silk lampshades. After their request for us to clean them, I asked if we could take one for testing. On the advice of a knowledgable drapery cleaner, I dipped them up and down in soapy water; then in clean clear water; then let dry.
Next day, they were 10 times brighter and cleaner! Absolutely no water stains, period.
Boy, that was one of the easiest but most profitable jobs we had ever done! We never told anyone our "secret"!
The very best;
Good Fortune to small businesses;
Ed valentine
cross-american corp.