How can I tell the age of a Pyrex dish?

The backstamp on the bottom of the dish is the first place to look. Pyrex changed its logo and markings several times over the decades, and collectors use these differences to date pieces. Older clear glass bakeware often has a more detailed stamp, while later opaque colored pieces have a simpler logo with the model number of the piece.

The pattern is another major clue. Each decorated pattern was introduced and retired at known times, so identifying your pattern in a vintage Pyrex guide will usually narrow the date to a range of years. Lettering style matters too: pieces marked in all capital letters generally come from the earlier era, while lowercase lettering on the bottom of some pieces is associated with later production.

Be aware that Pyrex sold in the United States later shifted to different glass, and newer pieces are not the same as the vintage borosilicate or opal glass many collectors seek. Original boxes, catalogs and advertisements are useful for confirming dates. If you have something unusual, collector groups and a dealer who handles vintage kitchenware can help confirm what it is.