Resist coated, design cut into resist and etched with Hydrofluoric Acid/Potassium Fluoride. A German development that was first used on a commercial scale by Richardson's, Stourbridge in 1857.
UK= Acid engraving US=Needle etching.
(Reference: Glass Fact File A-Z. Ivo Haanstra, UK 2001, ISBN 18400042900)