Vintage Pyrex 228 9" Pie Plate - USA Borosilicate Glass - 1950s Circular Stamp

Vintage Pyrex 228 9 Pie Plate - USA Borosilicate Glass - 1950s Circular Stamp  Product History & Authentication This piece is a classic example of mid-century American bakeware. You can verify its vintage status and material through several key markings:  • Glass Type: This plate is made of borosilicate glass. Historically, vintage Pyrex (stamped in all capital letters PYREX) used this thermal-shock-resistant formula. This allows the dish to handle significant temperature changes better than modern soda-lime glass (pyrex in lowercase), which was adopted later in the U.S. for consumer goods.  • The Logo (1950s): The circular backstamp configuration—with TRADE I 9-inch diameter.  	• D-15: These smaller alphanumeric codes usually refer to specific factory mold numbers or production runs rather than a date.