What is it? A stemmed sugar made by Brockwitz of Germany in their "Kopenhagen" pattern. Dates from the mid 1920s through the 1930s. The design is known to Carnival collectors as "Tartan". (There is also a variation to the pattern known to collectors as "Daisy & Cane").
It was imported into the UK by Jules Lang and Son - and they called the pattern "George".
How did they get this colour? It's pressed selenium red. We have had discussions about this in the past on the GMB and you might be able to find them - though I did actually delete a chunk of what I wrote once. Long story.
The short version is this. Red is a difficult colour to strike. Using selenium in the batch made it possible. The red, however, has a habit of turning back to yellow or going all the way to black. Often pressed red shows a yellowing in the very centre or around the edges. This is what Carnival collectors call amberina (or reversed amberina). It is not the original Locke / purist Amberina, but nevertheless it is what a lot of people refer to as amberina.
It is, put simply, pressed selenium red that has not struck fully and completely. Quite a lot of pressed red shows a little yellow somewhere.
It's gorgeous. A beautiful piece of glass.