hi - regret I'm no wiser than you as to an origin. Looking at the red decoration, first impressions are that it's been created in a manner similar to cameo - either a manual process to create the frieze or, possibly more likely, an acid etched style. The depth of the intaglio pattern appears quite substantial - in places almost back to the base white/cream colour. Just a personal take on the style of the decoration doesn't off hand make me think Spanish or Moorish, but who knows, you could well be correct.
The red decoration has a very geometric look - an absence of freehand styling perhaps - might this suggest a mechanical means? You don't mention wear - does the base wear suggest this might have the sort of age to take it back to c. 1900 - 1920? Appreciate your frustration, but the world is knee deep in unattributed glass - both shoddy, and classy such as this piece, and regret we have to live with this disappointment - it's maddening when a good piece lacks provenance in the form of a back stamp.
Was this an estate sale piece - any clues from that source as to it's history? Sorry to appear dim, but don't quite follow your comments ................. "The rougher glass on the outside is separated with a thin layer of white, then a super smooth layer of yellow on the inside." If you have the time perhaps you might clarify if possible. thanks
Very interesting piece - we do our best to help, but fail, often.
