Since glassware is fired on,, not painted on (except for those hand painted items) I don`t think anything would hurt the finish !! Might try a blow dryer as the heat should soften it as well and would be less messy !! If that doesn`t work throw it in a bucket of mineral spirits and let it sit a day or so !! You may be able to easily scrape it off then !! Just be careful with that razor blade,, it can easily scrape the surface off as well !! Try using a plastic scraper !!