├ A Glossary of Terms ├ Dating Pyrex Kitchenware ├ Pyrex Ware Patterns │├ Pyrex Pattern List │├ Pyrex Pattern Browser │└ Pyrex Pattern Timeline │ ├ Standard Patterns │ └ Non-Standard Patterns ├ Pyrex Opal Ware Shapes ├ Pyrex Model Numbers ├ About Pyrex Item Numbers ├ About Pyrex Colors ├ Pyrex Solid Colors ID Chart ├ Pyrex Promo Accessory ID ├ Vintage Pyrex Advertising ├ Pyrex Catalogs & Brochures ├ Patent Database ├ Videos & Links └ Accessories/Books/Apparel Estimating the age of Pyrex opal glass kitchenware can most often be done by observing a few basic characteristics. Production of opal ware commenced in 1936 after the merger with Mac Beth-Evans Glass Co. The plant there would be used to produce a more durable messware for the military. in a downward curve below forming a broken circle of sorts around the name. No model number or other information was included on the earliest pieces. 1950 or shortly thereafter, the registered trademark symbol "®" was added below the name, the encircling wording became TRADE MARK above the name, with MADE IN U. These appear to be related to either molds or production runs. Patterns The first pieces to have a decorative graphical pattern applied appear to have debuted in 1956.While colors and styles of decoration reflected consumer tastes at the time of production, the first thing to look at is the backstamp. But the product would not be branded Pyrex until the debut of kitchenware made from it nearly a decade later. New patterns were introduced in keeping with changing tastes, so they can also give clues as to time period.After 1959, the top surfaces were smooth and the undersides were fluted lengthwise.#500 dishes sold in 1959 and after in any color or patterns, therefore, should have the later style lids.Sometime in the 1960s, the circular configuration of backstamps gave way to a more straight text format consisting of PYREX ® in larger letters with model and capacity information in smaller characters above, and MADE IN U.On many pieces, various numbers and sometimes letters are seen in and around the backstamp.
A revised backstamp, with PATENTED above PYREX and MAY 27, 1919 below, was used after that date through 1924. A model number and, later, the capacity in pints or quarts were added above, and OVEN WARE below. Later pieces are also recognizable by, instead of "MADE IN U. A.", the the wording "by CORNING, Corning, NY, USA" with the verbiage NO BROILER OR STOVETOP or, later, BAKING AND MICROWAVE below.It was not until a few years later that the largest bowl was offered in open stock and also in red.Any 4-quart #404 bowl in a color of other than yellow must therefore be dated no earlier than 1949.The shade of blue on the 1-1/2 pint #401 bowl included in the 1968 revised color combo #400 set is different from that of any previously seen.Since the Cinderella design pieces were first introduced in 1958, they must all date from then or after.Backstamps On the bottom of most every genuine Pyrex opalware article is an embossed set of markings which contains a variety of information. The backstamp seen on various items prior to that echoes a Mac Beth-Evans trademark, but one not previously used on their glassware: that of a glassblower, or "gaffer", nicknamed "Little Joe". Since pattern collections and promotional pieces were available for relatively finite periods, knowing their years of introduction and discontinuance can also help narrow down dating somewhat.While technically a trademark, it is most often seen referred to as a backstamp. The configuration of the backstamp would undergo a few revisions after the introduction of opal glass kitchenware in 1945. A listing of patterns by year of introduction can be found .The different backstamp styles, consistent with the era of manufacture, serve to identify from which timeframe an individual example was made.Lids original to each would also be period correct.A revised backstamp, with PATENTED above PYREX and MAY 27, 1919 below, was used after that date through 1924.A model number and, later, the capacity in pints or quarts were added above, and OVEN WARE below.