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corningware not flameware anymore; corelle not always made of

updated sun 2 mar 08


Helen Bates on sat 1 mar 08

sandwiched glass; Pyrex and "downshock"; French tempered glass

Corningware(tm) is no longer made of the glass-ceramic material that
could be used on the stove, in the oven and under the broiler:

Some, not all Corelle(tm) is made of "Vitrelle," ie: the plates and bowls.
(Corelle also originally made cups from this difficult to break
material, not mugs, which were introduced later on.)
I have a set of these cups, which come with saucers:

Pyrex(tm) once made flameware (mid-1930's to late 1970's.)

> Pyrex pie plates and baking dishes are standard issue in the test kitchen, but over
> the years we've learned that they are prone to shattering when exposed to sudden
> and extreme temperature changes. Naturally, this prohibits their use under a broiler
> or over direct stovetop heat, but the tempered glass bakeware is also vulnerable to
> sudden drops in temperature, known in the industry as downshock. Downshock would
> result from adding cold liquid to a hot Pyrex dish or from placing a hot dish directly
> on a cold or wet surface. It is considered safe,however, to transfer a Pyrex dish
> directly from the refrigerator or freezer to a hot oven, provided it has been properly
> preheated--some ovens use the broiler element to heat up to the desired temperature.

The internet vendor Village Kitchen sells Luminarc products, many of
which are made of heat-proof glass:
What I find interesting is the mechanism of delayed breakage in these
products when damaged.
> Fully tempered glass may not break when it is damaged.
> Damage by impact after slipping or dropping seems to be
> the most often reported cause. The stress is stored and
> it may be released by shattering weeks or months later
> without obvious cause. Thermal stress often precipitates
> shattering. The release of the stored stress may cause
> the glass to scatter over a large area. Do not continue
> to use tempered glass that is damaged, it should be
> recycled and replaced with undamaged glass.
I feel lucky now that the one or two pieces of Corelle in my posession
that have broken did so immediately. One, I dropped on a concrete porch
floor onto a grain of sand. I think another broke many years later, but
the circumstances escape me. Otherwise, all my original pieces are
fine, as well as a few I have bought in a thrift store.

Mention is made by one of the posters in this last site
( of the metal heat diffuser that was meant to
be used with even the old flameware Pyrex... I have one of these,
probably for use with a Pyrex teapot I once had. I suppose the pot
broke at some point, but I don't remember now. I still have, and
sometimes use, the wire heat diffuser.

(Who has various pieces of earthenware, stoneware or porcelain pottery
in daily use, as well as her Corelle ;) )

Helen Bates
Belleville, Ontario, Canada
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