How to tell the COE of unknown glass

GoldSmithy · #1 2009-04-16, 9:56am

Being the newbie that I am, I just bought a used shop setup that has about 6 or seven lbs of glass rod. The person I bought it from does not know the COE of the glass. Is there a way to tell as I have some other glass with a COE of 104 and don't want to mix COEs. That's a no-no I am told. Any help will be GREATLY appreciated Smithy

shawnette · #2 2009-04-16, 10:09am

Not really. Some colors can be identified by sight, though. Do you have any black? If you do, pull a stringer and hold it up to the light. If it's really dark purple, not black, it's Effetre (Moretti) and the COE is 104. Based on our conversations, you most like received 104 with your setup, but it could be 90 (Bullseye). It's not likely that it's 96 or boro.

Can you post some photos of the rods?

Elizabeth Beads · #3 2009-04-16, 10:20am

Make some small test beads with a known 104 glass and the unidentified glass. I like to use inexpensive 104 Vertofond or Effetre clear to encase the mystery color. If the glass isn't compatible (i.e., fractures), it probably isn't 104 (although not all 104s play 100%nicely, which is why I wouldn't use Lauscha or ASK clear). Repeat test with a known 96 or 90 combined with the mystery glass to narrow it down further if it isn't 104. Hope that helps.

ArtcoInc · #4 2009-04-16, 10:49am

Take a rod of a know COE glass. As Erose suggested, use an inexpensive color. Heat the end of both the know glass and the unknown sample. Lay the hot end of one glass on top of the hot end of the other, like this:

Code:

known ==========
             ========== unknown

Fuse together *without twisting*, then pull into a thin stringer. Let cool.

If the stringer remains straight, the two glasses are "probably" the same COE. If the stringer curls up into a corkscrew, the two glasses are NOT the same COE.

Malcolm

Imaglassgal · #5 2009-04-16, 2:44pm

Cool idea, thanks for that one Malcolm!

SadiesJewels · #6 2009-04-16, 5:43pm

For that method you need to pull it of a certain length and take the middle 18" I believe. If that has a bend of a certain percentage (15% or was it measured in degrees?) it's incompatible. It means you need to be able to pull a good straight stringer ... lol.

Encased spacers also do the trick ... I had some unknown dichro I had to test and in the end I chose this method with careful notes.

Hayley · #7 2009-04-16, 5:48pm

Yes, for the stringer test, you need to pull to at least 18" and cut 6" off each end. Start with one end against a straight edge and see if it curves more than 1/4" at the other end or not. It doesn't need to curl up into a corkscrew for it to be incompatible.

In my experience, if it's more than 1/4", chances are it will crack.

Here is Arrow Springs' excellent instructions:
http://arrowsprings.com/html/stringe...patibilit.html

Karen Hardy · #8 2009-04-16, 7:14pm

Quote:

Originally Posted by GoldSmithy

Being the newbie that I am, I just bought a used shop setup that has about 6 or seven lbs of glass rod. The person I bought it from does not know the COE of the glass. Is there a way to tell as I have some other glass with a COE of 104 and don't want to mix COEs. That's a no-no I am told. Any help will be GREATLY appreciated Smithy

Your safest bet? Assume that you're going to have 6 or seven pounds
of spacers. Not a bad thing, you'll always need spacers to go with focals.

maren · #9 2009-04-16, 7:42pm

And, for newbies (I'm one myself), practicing spacers isn't exactly a bad thing.

squid · #10 2009-04-16, 8:05pm

How long are the rods? That might also be a clue. If they are 17" long, they are most likely BE. If you take a pic of some of them and post it along with the length, it's possible we might be able to help.

GoldSmithy · #11 2009-04-17, 5:56am

You guys are great...thanks for all the knowledge...Smithy

GinnyHampton · #12 2009-04-17, 6:10am

Quote:

Originally Posted by Karen Hardy

Your safest bet? Assume that you're going to have 6 or seven pounds
of spacers. Not a bad thing, you'll always need spacers to go with focals.

this is what I would do too!!

ginko · #13 2009-04-17, 6:21am

Quote:

Originally Posted by squid

How long are the rods? That might also be a clue. If they are 17" long, they are most likely BE. If you take a pic of some of them and post it along with the length, it's possible we might be able to help.

That is true. Just as a counterpoint, ArrowSprings tends to cut in 17" lengths, so it could be 104 or 96 as well.

I started to suggest a picture of all the colors together, but that would only work if we knew the glass came from the same source. There really isn't any good way to know, is there? Sounds like there is 7 pounds of great practice glass.

squid · #14 2009-04-17, 11:07pm

Quote:

Originally Posted by ginko

That is true. Just as a counterpoint, ArrowSprings tends to cut in 17" lengths, so it could be 104 or 96 as well.

I started to suggest a picture of all the colors together, but that would only work if we knew the glass came from the same source. There really isn't any good way to know, is there? Sounds like there is 7 pounds of great practice glass.

Darn them - darn them to heck!

oftenred · #15 2009-04-18, 4:57am

fuse each color to a piece of 104 clear and look at it through a polariscope...(just two pieces of polarized plastic or glass) you will see if there is any stress and you will know for sure...If stress is present do the same with a strip of 90 and 96 clear, and you will know exactly what you have...hope this helps