"Alchemy". Sapphire, if it's blue based, Emerald, if it's green based.
There should be an acid etched mark on the base, it might take a bit of peering to find it, it represents two blobs of glass on the blowing irons, inside a circle. One blob is bigger than the other.
Do have a search here for Dartington Studio Glass here, it was short lived (too expensive to produce) and although they stopped only recently, pieces are already very highly collectable!