Hello! How can I date this 'antique' bag I've found? How much is it worth? Gold/brass colour with blue lining. Heavy metal with chain strap, and magnets stick to it. I've seen similar envelope-shaped purses from the 1920's and some replicas in the 1970's...but haven't seen this seashell shape. Is that art-deco? Or modern? How do I verify what I've got? Pics attached, thanks!!