Produced all over Europe.
In Denmark they were produced at:
Holmegaard: 1890-1945 Kastrup: 1910-1950 Fyens: 1910-1950.
The individual glassfactories glasses are very difficult to distinguish from each other.
There may be color differences and minor differences in sizes due to the age of the glass.
Derby glasses, Holmegaard - Kastrup - Fyn Glassworks