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 recent article in Antique Week provided some valuable insight into dating Frankoma pottery.
Between 19 Frankoma used tan clay from the Ada, Oklahoma area.
Clicking on the mold number will take you to the first entry of a given piece in the Frankoma catalog.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.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.#500 dishes sold in 1959 and after in any color or patterns, therefore, should have the later style lids.Bear in mind, of course, that either style lid will fit any dish of corresponding size, so one can never assume a lid was originally sold with its dish unless it is found as new old stock.Clicking the links to the right of the date will take you to other photos if they are available on this site.├ 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. 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. 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.Many collectors now refer to the pottery from this era as Ada clay pieces.The Ada clay pieces are typically the most sought-after by pottery collectors. Frankoma collectors commonly refer to this clay as Sapulpa clay pre-1980.