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:
http://www.corningware.com/index.asp?pageId=99
Some, not all Corelle(tm) is made of "Vitrelle," ie: the plates and bowls.
http://www.corelle.com/index.asp?pageId=81
(Corelle also originally made cups from this difficult to break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:
http://images.etsy.com/all_images/3/37d/3ef/il_430xN.12556309.jpg
Pyrex(tm) once made flameware (mid-1930's to late 1970's.)
http://americastestkitchen.com/ibb/posts.aspx?postID=215084&viewreplies=true
> 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:
http://www.villagekitchen.com/mfg/arc/arc_tempered_glass.html
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
(Americastestkitchen.com) 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.
Helen
(Who has various pieces of earthenware, stoneware or porcelain pottery
in daily use, as well as her Corelle ;) )
--
Helen Bates
Belleville, Ontario, Canada
Clayarters' URLs: http://amsterlaw.com/clayart/
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