DUNCAN, GEORGE & SONS No. .306 and 307 (OMN) by Duncan, George & Sons (Pittsburgh-PA, Company Operated: 1874-1891), Unknown Date of Introduction
NOTE: Brad Gougeon - Early Duncan Glassware shows the two side by side and the only difference is height. Unfortunately the illustration does not give height or volume for either.
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Shape: Tumblers
Contributor: Robert Nathan Korn

Shape: Tumblers
Contributor: Andy Vaughn

Shape: Catalogue/Ads
Contributor: Sid Lethbridge

Shape: Tumblers
Contributor: Ed Perva

Shape: Tumblers
Contributor: John Ragsdale

Shape: Tumblers
Contributor: John Ragsdale