If glass articles are tapped, a dull thump is produced. All materials are easily purchased over the counter or by mail. and slowing the progression of psoriatic arthritis, Back Listened & answered questions. First of all, its always advisable to buy Waterford Crystal articles from a reputed retailer who vouches for the authenticity of the items. Old scratches in an original mark on an old piece of glass will be unfrosted because the glass and mark were scratched at the same time. New marks on old glass: Genuinely old marks applied at the time of manufacture will logically show scratches produced by normal wear.