The secret is simple—check the logo. If the brand name is in all capital letters, it's vintage Pyrex. If it's all lowercase, it's modern.
Pyrex dishes also hide a little secret code: Many contain a three- or four-digit number that corresponds to a specific dish. A series of Mixing Bowls will feature 401 (1.5 pint), 402 (1.5 quart), 403 (2.5 quart), 404 (4 quart). The iconic two-quart green-and-white casserole dish is a 232.
Broken or chipped Pyrex should be disposed of carefully in the waste bin.
Each Pyrex piece is assigned a model number, though some of the earliest sets of color ware pieces do not have them. Model numbers are typically found on the bottom of your glassware, though sometimes they are located elsewhere—look for them above the trademark on your dishes, and around handles and edges of lids.
The brand switched its formula in the 1950s to the soda lime glass, but recently started reintroducing borosilicate glass. Although both glasses are heat-resistant, borosilicate glass does better with extreme temperatures, making the vintage Pyrex pieces highly coveted by collectors.
Pattern. Patterned Pyrex—such as the 1956 Pink Daisy or the 1983 Colonial Mist—tend to be valuable as a collector's item. Other popular patterns include the 1957 Butterprint, which features an Amish couple and their crops, and has been valued at a few hundred dollars.
If it's all caps “PYREX,” it's vintage, made of borosilicate. If it's lower case “pyrex,” it's new, and it's soda lime. (In Europe, Pyrex is still made of borosilicate. So these recommendations only apply to Pyrex in the United States.)
How can you tell if a piece is real vintage Pyrex? The secret is simple—check the logo. If the brand name is in all capital letters, it's vintage Pyrex. If it's all lowercase, it's modern.
In 1915, the company launched its first Pyrex line (Pyrex combined "pie" and "Nonex") with 12 pieces, including pie plates and a loaf pan. The 8-ounce liquid measuring cup came out 10 years later; early versions had a closed, D-shaped handle and tick marks made out of molded glass.
It's lasted for decades. If it's all caps Pyrex, it's vintage, made of borosilicate. If it's lowercase Pyrex, it's new. And it's soda lime.
While vintage Pyrex is durable and even safer than newer tempered glass dishes, it's still essential to follow some precautions to ensure safe use. First, always bring your vintage Pyrex to room temperature before placing it in the oven.
Make Exceptions For Vintage Pyrex
When it comes to caring for those dear pieces, it's best to do nothing more than wash them by hand with gentle, clear, unscented dish soap and dry them with a soft cloth. You can find other tips for caring for vintage Pyrex on the Corning Museum of Glass website.
To avoid marring the finish, avoid stacking vintage Pyrex bowls upside down on top of each other. If you have pieces that won't be used often, store them in boxes with layers of heavy paper between each piece, and store the lids separately. If you keep them out for display, clean and dust them regularly.
Along with Butterprint, Gooseberry was one of the first patterns debuted on the new “Cinderella Bowls.” Cinderella Bowls were a series of large nested mixing bowls with a handle or spout on each side, which were designed by John Philip Johnson.
The Bottom Line
pyrex: Lowercase indication of containers that should not be heated in the oven or microwave. These are most likely made of soda-lime glass. PYREX: Uppercase label on cookware that is made of borosilicate glass and can be heated in a microwave or oven.
They are numbered as follows: 401 (1.5 pt), 402 (1.5 qt), 403 (2.5 qt), 404 (4 qt). The second type of mixing bowls are the Cinderella Mixing Bowls. These have handles and pour spouts on the sides. They are numbered as follows: 441 (1.5 pt), 442 (1.5 qt), 443 (2.5 qt), 444 (4 qt).
What Are the Patterns to Look For? The most sought-after pattern of all time is Lucky In Love. This promotional pattern was released in 1959, and very few pieces remain. The cheerful round casserole dish has green shamrocks and pink hearts and is encircled by blades of green grass.
Corning divested itself of the Corning Consumer Products Company (now known as Corelle Brands) in 1998 and production of consumer Pyrex products went with it. Its previous licensing of the name to Newell Cookware Europe remained in effect.
JAJ (short for James A Jobling) were the producers of PYREX tableware, casserole dishes and other bakeware in the United Kingdom from 1922 until the plant (in Sunderland, England) closed in 2007.
The best way is to look at the bottom of the product. My vintage Pyrex, which is at least 40 years old, and definitely boro-silicate, reads “Not For Lab Or Stovetop Use - Corning N.Y. - U.S.A. - 516 - PYREX.” Newer products made of soda-lime glass do not read Corning N.Y., nor are they made by Corning.
If the logo is in upper case lettering, PYREX, it's most likely made of borosilicate, and thus safer. The lowercase lettering is most likely made of soda-lime glass, so take extra care after any high-heat cooking.
It's tempered, meaning it's been heated and cooled in a manner that makes it more durable under future temperature fluctuations. It's less likely to break under an impact, and when it does, tempered glass breaks into diamond-like cubes instead of long, pointy shards, so it's a little safer to deal with.
One of the ways that collectors know what to look for is the three or four-digit number codes pressed into the bottom of each piece. If you've ever flipped over your pie plate or casserole dish and wondered what all those numbers are about, they're simply product codes that are assigned to each style and size of dish.
Vintage Pyrex Stamp and Logo
Flip over your piece and look at it carefully. It will have a stamp that can help you date it: 1940s and 1950s - The oldest Pyrex markings should be on the bottom of glass pieces and feature Pyrex in all capital letters inside a circle with CG for Corning Glassworks.
In 1968, a Corning retail promotional sheet states that “Four traditional colors give that special 'Americana' touch to the Early American collection.” From then on the Multicolor bowls were a part of the Early American collection, which was available between 1962 and 1971.