COE Does Not Equal Compatibility

houptdavid · #1 2013-03-03, 9:42am

http://www.bullseyeglass.com/images/...chnotes_03.pdf

Mitosis Glass · #2 2013-03-03, 10:06am

Excellent article. Thank you for posting it.

patienthand · #3 2013-03-03, 12:00pm

have not read it, but the statement is correct.

Janetlee · #4 2013-03-03, 4:15pm

Thanks David for posting the link.
Janet

Lisi · #5 2013-03-03, 10:59pm

Thanks! I have wondered about viscosity of different glasses in the same bead, from day 1 of my beadmaking career. It always did make me a little nervous.

LarryC · #6 2013-03-04, 11:20am

Unfortunately no one reports on viscosity so COE is the only measure from the manufacturer that the consumer has. As such viscosity may also vary batch to batch without the consumer knowing until it is too late.

Double Helix Glassworks · #7 2013-03-04, 3:15pm

We use strain polarimetry to determine compatibility parameters and fit. We test against a single, repeatable, (though somewhat arbitrary) constant, a certain batch of Effetre 004 clear. The fit testing process gives us strain in PSI, which is a fairly accurate and specific measure of compatibility, and allows us to adjust each batch, if necessary, to more closely approach the prefered "zero".

Is it 104? I don't really know. Dilatometric testing is often only accurate to +/- 2 coe points, which is a margin of error way outside of our in-house testing parameters, in addition to being somewhat irrelevant in light of the aforementioned viscosity, annealing point, and strain point issues.

Rough_necked · #8 2013-03-04, 4:19pm

What happens when you run out of the one specific batch?

I have not had any issues with double helix glass. Just curious as it is arbitrary anyways.

Double Helix Glassworks · #9 2013-03-04, 4:28pm

When we get low, we go to Frantz Art Glass, and take samples of all the bundles of 5mm clear in the building. Then we run polarimetric testing on the "new" clear vs the "old" clear until we find one that yields "zero" PSI, and buy the 10 kilo bundles that yielded zero PSI strain.

patienthand · #10 2013-03-05, 5:20am

an example in real life for me of COE not meaning compatible... I learned soft glass blown work from Jean Boutz using 90 coe tubing. All his colors came out of europe and were tested over a period of years. when I started doing glass about 35 years ago, most of his color stash was already 20 or more years old.

the 90s coe tubing is very soft and drippy stuff, it is lead based. I have been trying and testing a lot of the bullseye 90 coe rod, much of that is rather stiff, and it does not work in my application. Some of the very soft and runny colors do work.

then you add in the added factor of wanting to use more than one color on a thinly blown piece and you have to test all over again.

I really wish I could find some soft 90 coe color rod, or some standard wall 104 tubing.. the 104 tubing I can find is bloody expensive and hand pulled and VERY thin.. then its test all that glass and color as well....

I really want to keep alive the tradition of the blown work I learned, but getting compatible glasses is not an easy thing.

shawnette · #11 2013-03-05, 7:09am

Quote:

Originally Posted by patienthand

an example in real life for me of COE not meaning compatible... I learned soft glass blown work from Jean Boutz using 90 coe tubing. All his colors came out of europe and were tested over a period of years. when I started doing glass about 35 years ago, most of his color stash was already 20 or more years old.

the 90s coe tubing is very soft and drippy stuff, it is lead based. I have been trying and testing a lot of the bullseye 90 coe rod, much of that is rather stiff, and it does not work in my application. Some of the very soft and runny colors do work.

then you add in the added factor of wanting to use more than one color on a thinly blown piece and you have to test all over again.

I really wish I could find some soft 90 coe color rod, or some standard wall 104 tubing.. the 104 tubing I can find is bloody expensive and hand pulled and VERY thin.. then its test all that glass and color as well....

I really want to keep alive the tradition of the blown work I learned, but getting compatible glasses is not an easy thing.

Have you tried the chandelier glass the Arrow Springs has for $5/lb? It's 104 with 2mm wall. I've thought about ordering some, but never got around to it.