Causes of Cracks
Pyrex notes that any type of glass can unexpectedly crack or shatter, including Pyrex glass, also known as borosilicate. The intense heat from a gas stove’s burner or top places Pyrex under too much stress. Pyrex notes that any strong heat source, such as a stove top, barbecue grill, broiler or toaster oven, heats up too fast and too unevenly for Pyrex glass to accommodate. Pyrex Flameware pieces may be too old and stressed by previous stove top use to risk cooking with them.
If harsh detergents other than dish soap are used to clean Pyrex Flameware, the inside of the piece is scratched, notes Pyrex collector website Pyrex Love. Pyrex Flameware was not made to withstand the high temperatures of a dishwasher. Pyrex items, including any pieces in the Flameware line, should be soaked in hot water to loosen any baked-on mess. Any Flameware pieces a collector purchases now may well have been cleaned in a way that left scratches, even if the scratches cannot be seen. This makes Flameware too risky to use for cooking.
Never use any type of Pyrex on the burners of a gas stove or an electric stove. The Pyrex will not withstand the intense temperature changes and will shatter, according to Pyrex. To avoid breakage, never place a Pyrex item directly from the freezer into an oven. Always pre-heat the oven before placing a Pyrex item inside. Place a small amount of liquid, broth or gravy in pans containing meat or vegetables. The liquid will help heat the pan evenly.
Pyrex Flameware is too valuable to be used for everyday cooking. The line was made from 1936 to 1979. Older pieces have a handle made of Pyrex glass while newer pieces have a detachable aluminum handle. Individual pieces advertised for $1.50 in a 1950 edition of “Ladies Home Journal” sell for $20 on eBay as of 2011. Pieces in better condition bring higher prices.