Arthur Dent
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Chipped Condenser
Hi folks,
I bought yesterday a nice Pyrex condenser with 19/38 ground glass tapers, but it has a chipped spout!
So I was contemplating the best method to "repair" the thing without shattering it. I have repaired chipped borosilicate glass volumetric pipettes
before by using my dremel tool with the diamond cutting disk and it works pretty well! It does a great job when cutting through glass tubing without
shattering it and I can also polish off jagged bits and sharp edges. So that's probably the way I'll go to repair the chipped spout.
But then to smooth-off the grated surface, I usually use a small butane torch to bring the glass edges to reddish orange and it does a fair job. I
don't mind doing it on cheap pipettes, but the condenser is a much more valuable piece of gear and I don't want to "weaken" the glass where I'll heat
it up...
I have to admit that I am truly unfamiliar with the art of glass manipulation (bending/annealing/joining). Does anyone have tips on how to perform
that particular repair for my condenser? and while we're at it, can anyone recommend a starter's guide on the art of bending glass?
Thanks!
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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Magpie
lab constructor
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I have run into a similar problem on my broken buret. I cleaned up the edge with a diamond cut-off wheel but it is still rough. I just left it that
way.
Have you seen the book in the forum library on glassblowing?
The single most important condition for a successful synthesis is good mixing - Nicodem
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a_bab
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Even if he did see it unfortunately glassblowing is one of those skills that would take some 20 years to master. 5 more years and you get shaky hands,
then retire. Bunzen was a known to be a good glass blower; he made most of his equipment himself. He also stated that a real chemist must ideally
learn this skill.
There are small operations and repairs such as the described ones (cutting a chipped part, flame-polishing the sharp edges), but when it comes to
fixing up a crack that's pretty much it. A real glassblower can do it.
It may sound crazy but I once had the opportunity of getting the full gear of a retired lab glass blower for free (all kinds of burners, graphite
shapers, pinchers and such, even pre-ground standard joints ment to be glued to different glass equipment).
On a second thought I didn't take it since I'll never have the time nor the interest in learning this wonderful art of glassblowing, let alone the
full oxygen/propane lines that those burners needed.
[Edited on 5-2-2011 by a_bab]
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garage chemist
chemical wizard
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Don't repair it, leave it that way. The chip doesn't impair operation in any way.
If you try to flame-polish the chipped area, you will invariably deform the joint sufficiently to make an airtight seal impossible.
Since you said that this condenser is valuable to you, don't risk ruining it with repair attempts.
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Arthur Dent
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Indeed, I downloaded the book in question from the library and, although it gives interesting tips on bending glass tubing and basic glass
manipulation techniques, it's way over the top, describing elaborate glass-blowing equipment and high level techniques that I do not intend to use.
(I'd rather buy my condensers, not make them myself!)
I did learn interesing stuff though in this document and I went ahead repairing my condenser with my diamond cutting disk to just trim the broken
edges until I had a relatively smooth unpolished surface and just let it be, as Magpie suggested... I was apprehensive at the idea of using a flame
that near to a ground glass joint.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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Contrabasso
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When I worked in a pro lab I used to spend an hour a month or so gently polishing chipped glassware with wet n dry abrasive paper from 120 grit to
2400 grit. I could easily remove sharp edges that would otherwise cut you while assembling or using things.
Fortunately the lab next door was a metallurgical preparation area with stocks of circular abrasive discs.
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Arthur Dent
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Now that i've got my condenser all squared up  I read the rest of the book on
glassblowing. Fascinating piece of work! From the book, the hardest trick to master is to avoid the inside of the tube from collapsing when it's
heated and bent, by gently blowing inside the tube; 
i'll try my hand at the art of bending glass tubing soon. I need to make myself a few pieces of tubing with specific bends and lenghts (for gas
scrubbers and distillation apparatus joints) so i'll try to find a cheap source of glass tubes.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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Magpie
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Try these folks:
http://www.frantzartglass.com/
Good glass without the fancy scientific house prices.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Phosphor-ing
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http://www.ecu.edu/glassblowing/
Try this site for some general info on scientific glassblowing.
"The nine most terrifying words in the English language are: 'I'm from the government and I'm here to help.'" -Ronald Reagan
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watson.fawkes
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Quote: Originally posted by Arthur Dent  | | From the book, the hardest trick to master is to avoid the inside of the tube from collapsing when it's heated and bent, by gently blowing inside the
tube; |
It maybe the first serious
trick, not the hardest. Heat-softened glass responds to different forces: gravity, surface tension, air pressure, contact from tools, forces
transmitted from the cold end. The craft skills involving glass all involve learning how to manipulate and balance these.
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