Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Glassware Imperfections?
hectic
Harmless
*




Posts: 6
Registered: 23-2-2008
Member Is Offline

Mood: No Mood

[*] posted on 15-7-2009 at 15:11
Glassware Imperfections?


Throughout my years of collecting chemistry glassware I've ocassionally seen lines similar to, but not quite the same as, a crack. The lines are typically perfectly straight and very narrow. They resemble a scratch more than a crack (I.e. they are whitish) and have a shape resembling a very elongated, strechted-out grain of rice (do not appear to be air bubbles - too opaque). The lines usually cannot be felt with a finger, so are likely internal.

Here's the part where you may say "ahah!" - strangely, they only seem to appear on wide, cylidrical expanses of glass and always running vertical on a sidewall (that is vertical on, say, a beaker that is siting on it's bottom). For instance, Ive noticed them on jacketed glassware, glass buchner funnels, sox extractors, beakers, etc. - anything cylindrical. And I believe I've seen them only on the clear glass, never the joints. I've also seen marks that appear to be the same on quartz tubing.

Does anyone know what the term for these is so I may have starting point to dig up some hazard information on them? I'm thinking they may be some type of glass stress, but they should have a name based on the frequency that I've observed them.

I've never been concerned until I saw one on Pyrex beaker I plan to use. Here, heat may be an issue.

BTW - I've even seen one these imperfections on a unopened box piece of Ace glassware, so it's not an issue of cleaning or usage.

Thanks!
View user's profile View All Posts By User
FrankRizzo
Hazard to Others
***




Posts: 200
Registered: 9-2-2004
Member Is Offline

Mood: No Mood

[*] posted on 16-7-2009 at 14:08


hectic,

Can you post a photo?
View user's profile View All Posts By User
chemrox
International Hazard
*****




Posts: 2953
Registered: 18-1-2007
Location: UTM
Member Is Offline

Mood: LaGrangian

[*] posted on 16-7-2009 at 22:29


I've seen these too. Poor glassblowing technique can provide these. I think there's a kind of bubble with a frosting within caused by a temperature drop or moisture trace in the bubble. This is speculation. It sort of depends where it is and how big it is whether to be concerned. I won't put a vacuum on anything that shows an opaque fault or scratch anywhere near the main bag.



"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
View user's profile View All Posts By User
Foss_Jeane
Harmless
*




Posts: 40
Registered: 14-5-2008
Member Is Offline

Mood: No Mood

[*] posted on 21-7-2009 at 22:24


I've seen the same thing in glassware as well as glass vacuum tubes. I've never had glassware break because of that, and I haven't had any vacuum tube implosions either. No idea what causes that, but it's not a prob.
View user's profile View All Posts By User
entropy51
Gone, but not forgotten
*****




Posts: 1612
Registered: 30-5-2009
Member Is Offline

Mood: Fissile

[*] posted on 22-7-2009 at 09:06


For what it's worth, one of the glassblowing books on the web (can't remember which one) describes the different types of defects and their implications for glassware integrity. Try forum library, google books, archive.org if you are still wondering.

I've seen these defects every now and then but have not (yet) had a failure due to one. I'd be a little more careful if I intended to use the glass under vacuum or high heat.
View user's profile View All Posts By User
wpenrose
Harmless
*




Posts: 17
Registered: 17-6-2007
Member Is Offline

Mood: No Mood

[*] posted on 23-7-2009 at 21:11


I've seen them often. My inclination is,

- if new, send them back

- if out of warranty, discard or demote to use with nontoxic, noncorrosive, nonheating, atmospheric pressure applications

In fact, it would be interesting to break one of these flasks by impact near the imperfection to see how the break propagates.

Dangerous Bill
View user's profile View All Posts By User
watson.fawkes
International Hazard
*****




Posts: 2793
Registered: 16-8-2008
Member Is Offline

Mood: No Mood

[*] posted on 24-7-2009 at 06:15


I've deferred posting my thoughts on the question in case someone had a definitive answer, which I don't, so treat the following as an educated guess.

A whole lot of glassware is manufactured by dropping molten glass through a die in the bottom of a melt furnace. Think of pasta extrusion, except with hot glass. It seems to me that a streak defect aligned with the axis of extrusion comes from something in the melt that gets elongated in the extrusion process. My best guess about the something is that it's a pocket of dissolved or trapped gas that boils out of solution when the pressure changes from whatever it is at the bottom of the melt to ambient pressure after the extrusion nozzle. The gas might have been present as such in the melt, or it might be a bit of carbonate that reacts down to the oxide.
View user's profile View All Posts By User
mwechtal
Harmless
*




Posts: 1
Registered: 6-11-2009
Member Is Offline

Mood: No Mood

[*] posted on 6-11-2009 at 18:59
Glass defect terms


Quote: Originally posted by hectic  
Throughout my years of collecting chemistry glassware I've ocassionally seen lines similar to, but not quite the same as, a crack. The lines are typically perfectly straight and very narrow. They resemble a scratch more than a crack (I.e. they are whitish) and have a shape resembling a very elongated, strechted-out grain of rice (do not appear to be air bubbles - too opaque). The lines usually cannot be felt with a finger, so are likely internal.

Here's the part where you may say "ahah!" - strangely, they only seem to appear on wide, cylidrical expanses of glass and always running vertical on a sidewall (that is vertical on, say, a beaker that is siting on it's bottom). For instance, Ive noticed them on jacketed glassware, glass buchner funnels, sox extractors, beakers, etc. - anything cylindrical. And I believe I've seen them only on the clear glass, never the joints. I've also seen marks that appear to be the same on quartz tubing.

Does anyone know what the term for these is so I may have starting point to dig up some hazard information on them? I'm thinking they may be some type of glass stress, but they should have a name based on the frequency that I've observed them.

I've never been concerned until I saw one on Pyrex beaker I plan to use. Here, heat may be an issue.

BTW - I've even seen one these imperfections on a unopened box piece of Ace glassware, so it's not an issue of cleaning or usage.

Thanks!


I just joined, and saw this note. Since I have worked in the glass industry, I can tell you something about defects, but it's hard to diagnose one with just a description.

Un-melted batch / refractory is called a stone.

Tiny bubbles are called seeds.

An area that's overheated and/or exposed to too much O2 looks like tiny crystals, and is called de-vitrification.

An area that has glass of a slightly different composition (melted but not well mixed) is called cord especially if it is drawn out.

Any defect could be a cause for concern, depending on the use to which you put the glassware.

Mike
View user's profile View All Posts By User

  Go To Top