Detecting Fake and Forged Acid Marks on Glass
1. New marks on old glass: Genuinely old marks applied at the time of manufacture will logically show scratches produced by normal wear. In other words, scratches will go through original marks, as shown below, left. Many new marks applied to old but originally unmarked pieces will often be placed over scratches. Under a 10X loupe, you can usually see the acid in these new marks flowing into the old scratches.
2. Smudges and fill-ins Many new acid-stamped marks have portions of letters filled in, some parts of letters may be missing. Other than normal wear, the great majority of original acid-stamped Czech marks are uniformly even. Filled-in letters and badly smeared letters are seldom found in original marks.
3. Lettering appears as an outline Many new acid-stamped marks appear as etched outlines with the interior of letters not etched. Although this effect can be found in original ink- stamped marks, original acid-stamped letters are generally completely and uniformly filled in.