My viola, unfortunately, seems to have entered a bout of illness. I put it away in its case at the start of the summer, several weeks ago, and having got it out today to have a go with it, I noticed tht the G string (made by Dominant) seems to have tiny green blobs going all the way up it. These blobs rub away, but the wrapping on the string is dull underneath them, while the rest of the string is shiny. They appear to be located only on the G string, the rest of the viola is fine. Any ideas what it is, or what to do about it?

MY guess is that the green is copper carbonate. If the strings contain copper they may start to corrode, reacting with carbon dioxide in the air. Rather like copper domed buildings which turn green.