Colored Crystal Bowl - Smoky Blue and Brown

This amazing bowl goes from smoky brown at the base to a smoky blue at the top. It has optic ridges that are straight, not twisted. The rim is cut and polished. Some minor shelf wear on the base.
6 1/4" tall x 8 5/8" across.

Can't find anything like it on the web. What words would you use to search? I've tried ombre, two toned, optic crystal...

Frank Thrower? Wedgwood? Dartington? I am really at a loss.