and very attractive it is too. If I may add a little to the information already given........cruet is indeed the correct name applied to a container for a liquid condiment (for vinegar, oil, garlic juice, lemon juice etc.) - and if the contents are dry (as in pepper, mustard or sugar) then the container becomes a 'castor'. Often seen in sets, they were housed in wooden or silver stands, and it does seem that a glass underplate is unusual. The colour 'flashing' is typical of the origins that Lustrousstone indicates, and no doubt is still produced like that. The technique of firing a coloured stain onto a clear glass ground - then cutting to give the impression of cased glass is probably attributable to the Bohemians - ruby or amber being favourite colours. I may be correct in saying that the amber, such as this one, is produced by painting the glass with a derivative of silver suphide (then firing) - and the ruby by using a colloidal solution containing gold - but I may well be wrong (even very wrong).

. Date wise it may well be nigh on impossible to be even reasably accurate, but somewhere between 1900 and 1940.
Ref. (for some of the above only) - British Glass 1800 - 1914 - Charles Hajdamach......1991.