Thank you very much, Dirk and Astrid!
The Gralglas book is already on the wishlist for my next birthday...
Regarding the Zwiesel vase: I looked in to my favourite glass book again, '20th century factory glass' by Lesley Jackson, and as usual I am surprised by the profound information found in it (but too few pics).
"... In 1972 the factory changed its name to Schott-Zwiesel-Glaswerke AG. From this date designs were marketed anonymously as Atelier Schott-Zwiesel, although most were designed by Wilhelm Kuchler until his retirement in 1986. During the early 1970s Kuchler oversaw the development of a range of hand-made art glass, including ... vases decorated with thick, treacly bands or streaks of blue and green glass."
So my vase was made post 1972, and Wilhelm Kuchler "oversaw" the designs during that time...