Original glass trade vintage ad for the  CLAYTON MAYERS COMPANY. Main office and factory was located on North Circular Road, London, England.  Crystolac Toughened Tumbler. how long do they last in use?  Look through the top of the glass at the wording engraved on the base, then look underneath the word Toughened.  If there is nothing, then it was made in 1940.  If there is one dot it was made in 1941, 2 dots made in 42, and so on. ​This old 1947 one-page trade magazine advertisement would display beautifully matted and framed.