The glassworks that eventually became Franz Welz, was founded in Bohemia in 1728, by the Kopp family. Welz involvement began in 1794, when Vaclav Weltz married Marie Anna Kopp (the "t" was later removed from the family name). In 1894, Franz Welz built a new facility in Klostergrab, which was named Antonienhütte, after his wife Antonie Schreiber. The factory was in production until around the 1930's. Franz Welz glass is most noted for a wide range of colourful artistic glassware produced during the early 1900's. Output at this time included spatter glass + tango glass, and was similar in style to Kralik glass. Welz glass can occasionally but rarely be found with labels, either with the word "Welz", or the initials "F.W.K." (for "Franz Welz Klostergrab"). Labels with the words "Royal Art Glass" can also be found almost exclusively on Welz production.
Sources: Much of this information was shared in the excellent Franz Welz Art Glass Collectors Facebook group, by Craig Orkney, who has been researching Welz glass for many years, and it is thanks to him that most of the attributions shown below have been made possible.