This well known John Derbyshire vase RD300300 dates from 1876.
It is usually seen in black, matt or gloss, but also in plain or frosted.
There appears to be something odd about the black covering of this piece. Usually, black glass from this period is a very dark amethyst, which may look deep purple or red under strong light.
This one is different. It looks like an amethyst / puce item which has had a black covering applied in some way.
A close up shows a black layer over the top, which can flake off to show the puce underneath.
I've recently seen a puce one without covering, which is a previously unknown colour for this registration.
Actually I think the "frosted" version is really a satin finish, or a coating of some sort. Maybe this was made by dipping a plain one in acid?
Does anyone know what process is being used here for black and white?