├ A Glossary of Terms ├ Dating Pyrex Kitchenware ├ Pyrex Opal Ware Shapes ├ Pyrex Ware Patterns │├ Pyrex Pattern Browser │└ Pyrex Pattern Timeline │ ├ Standard Patterns │ └ Non-Standard Patterns ├ Pyrex Model Numbers ├ About Pyrex Item Numbers ├ About Pyrex Colors ├ Pyrex Solid Colors ID Chart ├ Pyrex Promo Accessories 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.
Being embossed rather than incised, and the material being glass, it is obviously molded in rather than stamped. The following are general representations of the various backstamps, which may not look exactly the same on all shapes. Promotional patterns may have been available for as little as a holiday season or a year, standard patterns from two years to as long as a decade in a few instances.The early clear glass Pyrex ware backstamp was a simple circle with PYREX in an all-caps serif font with Corning Glassworks' CG monogram above and below. The backstamp on the earliest color ware included the word PYREX with the abbreviation T. Other Considerations The earliest colored nesting mixing bowls have a deep base ring, the bases on later ones being almost flat by comparison. The CG monogram is often mistaken for and referred to by collectors as a dollar sign, albeit a backwards one. 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 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. Starting in the mid-1970s, equivalent metric capacities were also embossed on pieces, therefore any seen so-marked can be dated positively later than that.
The older mixing bowls also have a thicker, more pronounced rim, but with no appreciable difference in capacity from later examples. Variations in the red 2-1/2 quart mixing bowls encountered are owed to their differing heritages.The earliest #402 bowl was definitely more of an orange-red hue, described in advertising as "Chinese Red".The red #402 bowl supplied with the 1970s Friendship pattern collection differs from both the 1950s red 402 and the shade of red-orange on the 402 sold as part of the 1968 revised #400 multi-color mixing bowl set.Side by side comparisons, however, are often necessary to distinguish among them.From the time of introduction, the #400 nesting mixing bowl set was offered only as a set and in the original colors.It was not until a few years later that the largest bowl was offered in open stock and also in red.