The glasses are quite thin. Unfortunately, they have a low-quality sticker on their bottom that leaves a lot of glue residue. After I tried to remove it with hot water... with soap... with general-purpose cleaning liquid (like Sweep), with alcohol... And it wouldn't "budge"... I ended up using turpentine. With turpentine and cotton, the glass was cleaned... I didn't know (but I confirmed it after searching) that turpentine, due to its chemical composition, can damage thin glass. So, be careful.