I picked up a small service of these tumblers / double old fashioneds from an estate sale.
At first glance I thought maybe Holmegaard or somebody for Dansk, but no hits on the search engines. So the design is interesting with an ebony disc base, and a floating ebony layer just below the ringed exterior. Measure 4 1/2" high and 3 3/8" across the base rim. The top half is relatively thin with a fire polished top rim.
As always, any guesstimates would be appreciated.