coppercone
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Inspecting and destressing glassware
So i heard you can use polariscopes to inspect glass for sketchynes.. Are there pictures and videos on how to do that?
And for modern glass with tapered ground glass joints is it possible to destress it yourself if you have a precise kiln? Is this practice advised?
I personally get paranioa from glass sometimes and i would like to know how to asertain its condition.
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aga
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Using your glassware is quite a definitive test.
If it breaks, then it was Bad glass.
If not, then you did some Chemistry and the glass was Good.
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BromicAcid
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Glassware is usually destressed in an annealing oven. It's common practice to destress glassware after doing any sort of repair or work on it. In
general use glassware should not become stressed unless it is heated and held at extreme temperatures. I think >250C counts as extreme but I could
be wrong. ACE glass has a pamphlet on borosilicate glass that describes the upper working temperature for normal and extreme use. I have seen people
use polariscopes on glassware but have not done it myself. It's my understanding that unless the issue is major it's difficult for a novice to spot
it. But people who are good with them can tell a lot.
Here you go:
https://www.aceglass.com/dpro/kb_article.php?ref=4347-TFBN-1...
[Edited on 6/21/2018 by BromicAcid]
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aga
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Who ever does any repair work on their glass ?
I just buy it from China - it's only ever gotten broken during shipping or cleaning.
Boiling H2SO4 is a bit over 250C.
Still works fine.
Maybe need to temper and anneal my tweezers tomorrow - not sure they'll stand up to my nose hairs.
Maybe my beakers are about to break. Best not use them until examined under an electron microscope.
Is this chair i'm sitting on safe ? What if it isn't ? OMG.
Maybe my laptop battery is about to explode. Best remove it and interview each lithium ion as to it's future intentions.
You never know - could be a radical in there 
Edit:
WOW. That's the 7000th pointless pile of crap i posted.
Seems you really can pile shit very high indeed.
[Edited on 21-6-2018 by aga]
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Dr.Bob
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I have used lab glass for 30 years and you are likely worrying too much unless you are doing actual glassblowing work. I would remove the worry and
stress with alcohol like most chemists do.
Glassware relaxes with time, so stress will slowly go away with time unless you heat it to serious temps. Even fixing a minor chip or loosening a
stuck stopper with a torch will not create that much stress, only heating the glass to working temps should create that much stress. But normal
usage will not stress glass, unless you drop it. I have flasks that are 20+ years old that I still use, much of my daily glassware is at least 10
years old, much is older, and it works fine. Even the stuff with scratches, etching, and small chips on the joints is fine, as long as their are no
cracks.
Once a flask is cracked, I don't use it for anything under vacuum or pressure, or much else either. I might use it for a messy RT reaction that I
don't value much that will ruin the flask, but only with a dish under it, in case it breaks. But I have not even had a cracked flask break in
normal use of just stirring a reaction at RT. Good examples are NaOH reactions, fluoride chemistry, polymers, chromium reactions, and other black
tar forming reactions, or things that might contaminate the flask badly.
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coppercone
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Aga I just don't see it as fun and games especially if its airless chemistry, pyrophoric, highly flammable, toxic, etc. I don't want to deal with
having to clean up a nasty spill or having a plume develop.
Also corrosive gasses suck and destroy property.
Even with a fume hood you can easily saturate it unless you get serious airflow, and make it look like your house is on fire. I also don't like paying
the chinese for anything really, they produce garbage for hobos
I also don't drink. I like neatness and order. That kind of cowboy shit gets narcotics, fire departments, ATF and even evacuation orders.
[Edited on 22-6-2018 by coppercone]
[Edited on 22-6-2018 by coppercone]
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coppercone
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Dr bob, really the internal stresses go away over time? I did not know that, I thought it got pretty much stuck. What kind of time constants are you
looking at?
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Dr.Bob
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Quote: Originally posted by coppercone  | | Dr bob, really the internal stresses go away over time? I did not know that, I thought it got pretty much stuck. What kind of time constants are you
looking at? |
I'm not saying that it anneals itself, just that unless it is stressed by working, it will not get stressed from normal use. But glass is a stiff
fluid, so over the years it will slowly anneal itself, but I am talking years and centuries. So if you work glass at torch temps, it is best to
anneal it, otherwise it is not needed.
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wg48
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That’s so important I have made it my signature.
Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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Dr.Bob
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The number of times I have used glassware above 200 C is pretty rare. There have been a few times, but not too many. But for most organic work, you
will rarely exceed that. Inorganic work may exceed those temps, but you would normally do that type of work in a crucible, metal vessel, or
specialty glassware. Vycor or quartz comes to mind, but even those are rare in most labs.
Doing acid digestions used to be a place for that type of heat and acid, but those reaction are now mostly done in Teflon labware in a lab microwave
now. But certainly boiling things in acids can be harsh.
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MöbiusMan
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If you get a polarising filter for a camera and put your glass between a white laptop screen and the the filter you can see the stresses if there are
any 
If chemistry was easy it would be called biology.
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