Found on busts, granites, Basalt vases, figurines, plaques, medallions, and cameos. It is assumed that Josiah Wedgwood used the mark at Burslem. Although this was not a fool proof system for dating purposes, because sometimes they overlapped and in some cases certain letters may provide you with possible dates for its production. Early Wedgwood works may be unmarked, but the presence of the correct mark is an indication that the piece is genuine and should allow you to determine its true age. Having lines inside and outside, the mark was impressed on Basalt or Etruria vases, but not seen on Jasper ware.
How to Date Orrefors Glass.
Allison Thompson's top article generates over views. Look for letters. However, sometimes this mark was also encircled, while in other cases the entire mark was raised rather than impressed. For a short period.