Technical Topics

Opal Pyrex:

Opal Pyrex was used in many cup styles until late 1986.  Confusingly, it has been stamped at various times with the name ‘Corning’ as well as ‘Pyrex’ and even 'Corelle', so the best way to identify it is by appearance.  Of all the materials discussed here, Opal Pyrex is the most translucent and looks slightly grey when compared to Corelle.  When all else fails, if it says, ‘No Stovetop or Broiler’ in embossed lettering then it's definitely Pyrex. 

There is a second kind of opal Pyrex used mid 1980s for cups in the ‘Livingware 2’ product line.  It is formulated to be a brighter white and is more opaque than usual.  Both types of opal Pyrex are excellent for microwave use, as is clear Pyrex. 

Corning Ware:

Real Corning Ware glass-ceramic was used in the manufacture of Corelle-matching cups in the late 1990s.  But it was short-lived, and soon after (in 2000 perhaps) all cups were manufactured overseas from stoneware.  These cups were made in white and Sandstone, and are slightly less glossy than Suprema and Centura.  Generally, cups made of real Corning Ware literally say ‘Corningware’ on the stamp.  Although the stamp does not mention it, they are safe for the microwave.  To add to the confusion, some cups actually made of Corning Ware are marked simply 'Corning'.  But similarly they make no mention of microwaves.  The stamps are essentially the same as the one pictured below, minus the word 'ware'.

Most cups made of real Corning Ware have the 'Corningware' brand.

(Please see "Glass Manufacture" in the left column for other glass types.)