Not really sure about your item yet, have looked at bit. the hallmark that sapphire posted is a old sheffield plate complany, and would be very old and valueable if it was a Sykes Sheffield plate item, but since your flask has a screw on top I would really doubt it to be sheffield plate. but you did mention that the plate has seen better days, most sheffield plate items has, but most likely it would have copper showing through. I will say that it is a very unique Flask to say the least, and would have many collectors will to pay $$.00 for it.