After much consideration I think this is a rummer from the Regency/Early Victorian era. It is 5 1/4" tall, with a 3 1/2" wide bowl and 3 1/8" foot. There is considerable wear on the foot but with only a very minimal contact area. The pontil is a ground out swirl and it has a blade knop. The bowl has some horizontal striations and a slightly grey colour, it may be my imagination but it seems to also have a slightly mauve tinge. Any thoughts ?