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. A listing of patterns by year of introduction can be found here. 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. New patterns were introduced in keeping with changing tastes, so they can also give clues as to time period. The first pieces to have a decorative graphical pattern applied appear to have debuted in 1956. These appear to be related to either molds or production runs. On many pieces, various numbers and sometimes letters are seen in and around the backstamp. Later pieces are also recognizable by, instead of "MADE IN U.S.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. Sometime in the late 1960s, the circular configuration of backstamps on refrigerator dishes 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.S.A. A model number and, later, the capacity in pints or quarts were added above, and OVEN WARE below. 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.S.A. No model number or other information was included on the earliest pieces. On some pieces, this was also enclosed in a ring. in a downward curve below forming a broken circle of sorts around the name. The backstamp on the earliest color ware round bowls included the word PYREX with the abbreviation T.M.
The following are general representations of the various backstamps, which may not look exactly the same on all shapes. The configuration of the backstamp would undergo a few revisions after the introduction of opal glass kitchenware in 1945. The backstamp seen on various items prior to that echoes a MacBeth-Evans trademark, but one not previously used on their glassware: that of a glassblower, or "gaffer", nicknamed "Little Joe". But the product would not be branded Pyrex until the debut of kitchenware made from it nearly a decade later. The plant there would be used to produce a more durable messware for the military. Production of opal ware commenced in 1936 after the merger with MacBeth-Evans Glass Co. The CG monogram is often mistaken for and referred to by collectors as a dollar sign, albeit a backwards one. below.Ī revised backstamp, with PATENTED above PYREX and below, was used after that date through 1924. 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. Being embossed rather than incised, and the material being glass, it is obviously molded in rather than stamped.
While technically a trademark, it is most often seen referred to as a backstamp. On the bottom of most every genuine Pyrex opalware article is an embossed set of markings which contains a variety of information.
While colors and styles of decoration reflected consumer tastes at the time of production, the first thing to look at is the backstamp. This mixing bowl is designed to fit Pyrex 326-PC plastic lid (sold separately).Estimating the age of Pyrex opal glass kitchenware can most often be done by observing a few basic characteristics. Providing enough space to the user to mix up meat fillings, salads, batters, doughs, etc., this bowl is sure to be a much-used staple in any professional or home kitchen. This 4qt mixing bowl is ideal for hand mixing ingredients as well as baking, storing, heating, and serving various food items. This glass bowl has a simple, classic design and is safe for use in microwave, pre-heated oven, freezer, and refrigerator, and can be easily washed using a dishwasher. The non-porous surface of this glass bowl does not absorb any odors or stains from food, ensuring its appearance for years of use. The Pyrex 326 is made using high-quality clear glass that gives the user the chance to keep a proper view of the food while it is being prepared.