a good starting point would be to look for glass, which has been made and decorated in Kamenický Šenov
(also look for the former german name Steinschönau to get further results).
I take it you´ve looked at the pieces very carefully so you haven´t missed a tiny signature in the painted
If you find a W.Berndt for example:ebay
But... these have been made over a long time and I´m almost sure you´d still be able to get quite
similar examples in this style in Czech Republic until today. But the date of your grandparents´acquiry
gives an early time frame of course.
I´m sure I´ve read other names on similar pieces, but I can´t recall them unfortunately...