I'm just looking for practical real-world experience.
Today I had a bit of old tea powder left in a Lipton powdered iced tea
Instead of throwing it out or chipping it out, I simply poured boiling
water into it and drank it from the jar.
Since I half expected the glass jar to break, I did this in the sink -
but to my surprise, the glass held the just-boiled water.
I realize that glass can be made out of many materials (e.g., Pyrex) ...
but I wonder ...
Is this the general experience that typical American glass jars hold up
to boiling water?
On Fri, 06 Jan 2012 21:00:46 -0500, Betelgeuse wrote:
Over 150 incidents of glass 'bakeware' shattered (some with serious
Borosilicon (often made in Europe) versus soda lime (which is more
They filled bakeware with dry sand, baked at 450 degrees F for 80
minutes, and then put it on wet graniteand.
The result was that 10/10 times the American-made soda lime bakeware
broke while the European Borosilicon didn't break (but most did at 500
Revealingly, the ancient American Borosilicon did last at 500 degrees.
On Sat, 7 Jan 2012 01:27:06 +0000 (UTC), Chuck Banshee
Glass jars can easily take the 200 or so degrees of hot water. What
will do them in is thermal shock where it is heated too quickly in one
spot compared to other spots. As in a flame, for instance. or
freezer to oven or reverse.
Glass jars are heated fairly high when filled with the contents and
sealed. Heat killing bacteria is what allows it to keep product safe.
On Sat, 07 Jan 2012 01:27:06 +0000, Chuck Banshee wrote:
An unexpected bonus was the fact that the glue under the wrap-around
label heated up enough to be easily balled off with a kitchen utensil.
Maybe we accidentally found a way to remove the under-label glue without
Like most materials, glass expands when heated.
Heat breaks glass vessels when the glass is nonuniform,
i.e. has varying densities at various places. If some parts
expand faster than others, this introduces stresses that
may break the vessel. It is generally supposed that
older glass vessels are more uniform than modern
ones, thus can accept more heat without breaking.
Well, not all "glass" is the same.
Pure quartz glass has a very low thermal coefficient of expansion.
Standard "Soda-Lime" glass has a relatively high thermal coefficient of
The "Boru-silicate" glass features a thermal coefficient of expansion
close to pure quartz. It's advantage over quartz is a MUCH lower
The original American Pyrex (r) was a Boru-silicate glass. Apparently,
the owners of the trademark decided that in the US market they would use
"tempered" soda-lime glass in place of the Boru-silicate glass.
The Tempered glass is good stuff. It's very, very break resistant and
is moderately resistant to thermal shock. (It's actually created via a
"thermal shock" process whereby the hot glass surface is suddenly
cooled; another process uses a "case hardening" process when Potassium
(K) replaces Sodium (Na). The potassium atom is a bit larger ad that
places the surface under stress which has the same effect as quickly
"tempering" the glass.
The neat thing about tempered glass is that when it does break it breaks
into small pieces which are unlikely to cause a fatal injury. OTOH,
true Pyrex (r) will, when broken, generate good sized slithers.
The types of lawsuits generated by broken tempered glass are as in the
noise as compared to that generated by broken soda-lime glass.
Watch out for broken tempered glass! While external to the vehicle, I
had a front windshield shatter, in moving about the vehicle to
retrieve items on the front seat, I gently brushed my back against the
shattered widnshield. I did NOT even feel the small shards cut through
my shirt and down into flesh until someone pointed out the blood
running down my back. So yes, not fatal, but still as sharp as a
Pyrex does not expand much when it is heated. I had two Pyrex one
quart storage bowls (7201 05) that got stuck together. I put ice
and salt in the inner one and put the outer one in very hot water.
The temperature difference was at least 120 degrees Fahrenheit. The
bowls were still stuck together. I did not see any change in
I have read (or seen on TV) that Russians often make tea in glass
tumblers. They put a metal spoon in the glass to keep it from
breaking. A silver spoon would conduct heat much better than a
stainless steel spoon but stainless would probably be good enough.
When a cat sits in a human's lap both the human and the cat are usually
happy. The human is happy because he thinks the cat is sitting on him/her
As others point out, it is the thermal stress that breaks the glass.
Pyrex type glass expands less and will take more stress but is too
expensive to use for throwaway jars. The cheap jars if heated slowly and
uniformly to minimize stress will take hot filling. In your case,
adding the hot water slowly with swirling would probably be OK.
Also not a good idea to microwave items in this type glass.
Owens-Corning sold the Pyrex brand name to a company that's now using
it for soda-lime glass (not heat-resistant).
I once canned some peaches and didn't get the air bubbles out of the
jars before putting them in the canner. The bottoms of the canning jars
popped off very neatly, as though they'd been cut with a glass cutter.
You probably had the lids too tight to begin with...air is supposed to
escape during the canning bath and then the lids seal as the jars cool.
Should tighten before boiling so that the rubber seal barely touches,
not tight. The rings, if separate, are then tightened after cooling.
Test lid with a tap ..
The major issue with any kind of glass is even heating and cooling. One
t'giving, getting the turkey ready, I moved an empty Pyrex pie plate
onto a burner on our glass cook top. Sat down to dinner in the dining
room and a couple of minutes later there was an explosion in the
kitchen. The burner had been left on, and there were long shards of
glass all over the kitchen. Don't want to know what it would have been
like if one of us had still been in the kitchen.
Learned from glass crafting that various glasses have differing COE
(coefficient of expansion, I think)...can put glass in a kiln to melt or
fuse it, but two different glasses to be fused should have same COE or
they cool at different rates and then crack. Took grandson to a
glassblowing class...way cool. He had thought about being a glassblower
but decided to make it just a hobby :o)
I did not see the Pyrex brand on my old canning jars and doubt that they
Here's a Wiki link:
When I worked in a lab, all our glassware was Pyrex. I'd repair or
modify things on occasion but the complicated stuff went to the labs
professional glass blower. It was important to anneal the glass after
modifying to remove stresses. Looking at glass with polarized lenses
can show stress points.
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