Sciencemadness Discussion Board

cheap glass beware!

chemrox - 25-4-2008 at 23:42

I have a flat bottom, three neck, 3L rb flask that had to go the glassblower to get it separated from the 6 cell Snyder column. It was made in India and the glassblower warned me not to pull a vacuum on it because the glass is so thin! The joints are out of round as well. Piece of shit I got on ebay. A lot of Chinese glass is fine but the stuff from India should be avoided.


MadHatter - 25-4-2008 at 23:48

That's what it sounds like. Good for measuring liquids but I'll never use it in heating
applications. Had an 800-ML beaker develop a crack after heating with just a slight

octave - 26-4-2008 at 20:31

Bomex is bad? I've used it for awhile and it seems fine to me, but then again maybe I'm just lucky :p .

The_Davster - 26-4-2008 at 20:32

We have been through this in other threads, bomex is just fine for standard chemistry with mild heating, but under any stressfull conditions it can and has been know to fail.

evil_lurker - 26-4-2008 at 20:46

Perhaps you should name the seller, or at least positively ID the brand so as other members can avoid purchasing the same.

chemrox - 26-4-2008 at 20:54

I am avoiding anything made in India for the present. There are a number of brands and I don't have access to all the names. I'll se if my glassblower knows though and post them if he can deliver.

undead_alchemist - 27-4-2008 at 22:06

The only Bomex glass what was made good was the items sold though VEE-GEE Scientific. All other Bomex glass was lower grade.
Also Bomex is now owned by Kimble Glassworks.

As for glass made in India. there are a few good glassworks.
Borosil brand. *was setup as a sister company to Corning, so glass is the same grade*
Glassco Brand. *made from Schott Brand glass*

Pulverulescent - 28-4-2008 at 05:11

Originally posted by chemrox
I'll se if my glassblower knows though and post them if he can deliver.

Your glassblower???
Jeez, some people are just born lucky, I guess!


Sauron - 28-4-2008 at 05:54

If joints are out of rounbd they will leak when a vacuum is pulled.

If the glass is crap, or too thin, it will fail under vacuum. Easy to test (behind a shield).

The real torture test is heat + vacuum. The major glass companies publish data for glass performance at temperature and under vacuum.

jimwig - 28-4-2008 at 11:06

repairing cheap glass may not be such a good idea.

the imported stuff just doesn't make the grade friends. stay with kimax, pyrex. and other brands of quality glass are the desired items.

although i am sure some of that is made in other countries-- at least its under (supposedly) the supervision and standard of the ASTM.

the chance for great profit is just too large. aka don.'t eat the tickle me elmo........ nor lick your collection of fishing sinkers. ya no?

it's one thing for us "older" folks but the kids--- another kettle of fish.... hahaha......

imho it is still mostly common sense but they are working on that aspect also --- "pay no attention to the man behind the mirror"

could the sons of bitches really have slaughtered those people in the world trade towers and others? hard -- very hard to believe but the (lackof) evidence says maybe so......

be ascared ===== be very ascared....

craZy jiM wGGns

[Edited on 28-4-2008 by jimwig]

bio2 - 28-4-2008 at 15:44

I've noticed that the Kimax boiling flasks made in Mexico are not as good as those from USA or Pyrex from UK.

They tend to sometimes have minor inclusions and joint tolerance is not as good.

One Mexican made Kimax Liebig condensor had to be discarded
because after full vacuum use it would always stick as the ground joint on the inlet end wouldn't completely seat.

All in all though, Kimbles Monterrey Mexico factory turns out
good stuff.

Any Mexican made Kimble glassware has "Mexico" enameled
onto the part.

[Edited on by bio2]

angelhair - 2-5-2008 at 19:28

I know a glass blower who is mixing the indian stuff with Duran when making condensers. He explained how the indian stuff is drawn up when manufactured and showed me how to identify it. You can see vertical striations in it.

He does it because the indian stuff is very cheap and the unsuspecting buyer has no idea.

MagicJigPipe - 2-5-2008 at 20:26

I have a couple of "unidentified" pieces of glassware. One is a 1000mL RB flask. I believe it was made by an independent glassblower as it simply says "1000mL" in blue text. One thing I noticed is that there was one imperfection on the side. I don't know much about working with glass but it is a little speck and if you rub your fingernail over it, it feels like a bump. Almost as if the glass folded in over itself in a millimeter sized spot. (it has a "generic" 24/40 joint)

What is this? Could it cause problems under vacuum?

Also, what is a good glass thickness for vacuum? I have ran all my flasks except the one above and a few others with vacuum and some heat but I would like to be able to tell without destroying the flasks.

chemrox - 2-5-2008 at 21:52

I only know when it feels and sounds too thin when you tap it. I suppose the right kind of caliper can reach in. I have some Chinese glass that has those little bumps and bubbles you're talking about. I was concerned about one and had my glassblower anneal it. Do you have access to a good glass man? If so have him inspect your flasks before you pull them down below say 7-10 mm. I have a plexiglass shield I can put between me and the evacuated system. It's easy to come by and cn be gotten out of the way when not wanted.

mick - 3-5-2008 at 11:17

If it was a flat bottom flask and not heavy walled, it is not designed to be used under vacuum. Round bottom flasks (rbf) are better.
If the glass blower mixes different brands of borosilicate glass from a few years ago i.e. pyrex, bomex, schott they all had different thermal expansion so they were not compatible. I helped move a lot of glass but it was all scrap because the company spec was different to the standard. Probably why they closed.

chemrox - 4-5-2008 at 05:54

What you say is true-about the falt bottom flask used for vacuum. I have pulled vac on those before though; without misadventure. I did use heavy wall material. What about adding joints to exsiting glassware? Glassblowers do it all the time. As I understand the practice, they get a "bag". The kind of thing you see on ebay a lot. An rb without any joints. Then they build the piece to a specified configuration of a joint or joints. So, doesn't that imply mixing borosilicates? BTW- I re-cycle the joints on broken pieces by giving them to the glassblower for jobs that require them. I got one particular joint stuck three times-another exampe of Indian glassware. I was sure I was doing something wrong until the last go-around when despite all precautions it was stuck again.

[Edited on 4-5-2008 by chemrox]