Fair warning.
 

I encased Effetere white with CIM Mediterranean Blue. And every one cracked. I'm not just pissed at the time they took but the wonderful murrini wasted.
It's hard to see them but they are there especially around the holes.

That bites Pat! Those are beautiful! I would be pissed too!

Ack, is that one of the new colors? So sorry, Pat. Beautiful work :(

Aww man. I got that with Marine, but it was fine for some other testers, so not sure if it was just a confluence of things in my case.

I think it is a new color. Maybe it would be ok with peace white. I just wanted to warn others about this.

Could it be a viscosity problem? Sometimes with fusing if you do an especially careful anneal you can avoid the problem. Don't know if that would work for beads. It doesn't always work for fusing.

Viscosity is problably the culprit as Deb L says. CIM glass all tends to be 'hard' glass and Itallian glass is 'softer, especially white and creams. Can probably be traced back to the sand used to make them. They are using from different deposits on the opposite sides of the world. I try to keep CIM with CIM.

Ummm, no...

Glassmaking sand is 99+ percent silica, whether sourced in Europe or Asia. There may be some difference in minor impurities such as iron, etc., but these would be small enough to result only in color differences (greenish tint for iron), not a major viscosity difference. Any potential viscosity and/or COE difference would depend on the overall composition of the glass, not the origin of the silica in it.

That's a shame. I have found that many transparents tend to crack over white alone, including rubino. I think it is because white is do soupy.

My solution is to make a core of transparent scrap, encase in a thin layer of white and then encase in your beautiful transparent. Give it a try and let us know how it turnout for you.

Very considerate of you to share your sorrow. I'm with fcfmountain - I just try to keep all the same glass with only the same glass.

How sad-they're beautiful!

Thanks for the heads up/

Georgia

Well that just stinks Pat! They were really pretty too. I had a bunch of that going on awhile ago and now only use it all by itself. I almost gave up on it but the colors are too pretty.

:( They're beautiful beads and a fantastic color. What a bummer.

Aww such a bummer. Such pretty beads. =(

In the 9 years I made beads I never heard of a "viscosity" issue. (???)

Patti, as I stated in my answer, I come from a fusing background where viscosity can matter. I said I didn't know if it was a problem with beads. They are small so maybe it isn't a problem? Obviously, something is wrong, whether it is a coe off, viscosity or something else. Either way the loss of such a beautiful set is very sad.

I have had lots of trouble with transparents cracking over a solid white core, even if they are all Effetre. I second the suggestion of a clear core with just a white coating before encasing!

What does CIM say? I understand they tout compatibility of their glass with soft glass.

Well! That explains why Halong over white kept cracking on me. I was sure it had to do with me not giving it enough heat when I was shaping, but then I tried with just simple round beads and the same thing happened. I'm going to try the clear, white, halong trick.

Thanks!

CIM blues tend to need higher annealing temps, and even then I don't know if that's any guarantee. I remember hearing about people having issues with Leaky Pen, Halong Bay and a few others. Kathy recommended annealing at 1040 or so.

Here is another case of just because it is the same COE does NOT mean compatibility, until companies test to a standard with a polariscope this will continue to be a problem for lampworkers

"Viscosity issue" is another way of saying the annealing temperature and/or strain points of different glasses are far enough apart to cause problems. This can - and does - happen with some lampworking glasses, even those with the same COE. Sometimes even those from the same manufacturer.

On top of that, some glasses can undergo a COE shift during working, and in extreme cases wind up incompatible even with themselves. So there are no simple answers to compatibility that can be universally applied.

I don't know the answer to the problem with the specific glasses mentioned above. But, as also mentioned above, sandwiching a thin layer of white between the other glass may help. This technique is one that has been used for a very long time to deal with problem glasses. It doesn't always succeed, but in some instances it can keep the overall stress below the point where it will crack the piece. While less technically demanding, in practice it can act like a graded seal in scientific glass, which is a method of joining glasses of different COE, such as 33 COE borosilicate to 90 COE soft glass, which is sometimes necessary in order to make glass to metal seals.

Brad

This is great info! Thank you!

You're welcome Karen! Hope it works for you.

I have another glass friend whose gorgeous bead has incompatibility cracks. This time the culprit was Peacock, another bluish CIM. Too bad, the CIM blues are so gorgeous.

Thank you Brad, for your input on this issue. It is interesting to learn from someone who actually makes glass rods and who really understands the chemistry involved :)

Awe shucks! Sorry, they were very pretty.

I'm so sorry. Those were lovely. :love: Angelique

OK, did someone say viscosity???I have to refer you to this very old- and very useful- discussion. I have wondered a bit about some of the CIM I've used as it has been fairly stiff. Anyway- here's a lot of info about viscosity.
http://lampworketc.com/forums/showth...ight=viscosity

I just read that thread and I hate to say it, but there's a lot more misinformation there than information.

There are only two posts in the thread that I would recommend anyone pay attention to, with a third that makes some sense if you already understand the subject, but only confuses the issue otherwise. (I think the third poster actually knows what he is talking about, but chose a very bad example to describe things.)

I consider the posts by Emiko and houptdavid to be the informative ones there.

Anyone who wants truly useful and factual information about compatibility, viscosity, and COE (as well as other glass stuff) should try to hunt down the booklet, "Glass Technology for the Studio", by (now retired) Corning Glass Scientist Frank Woolley. A while back it could be ordered from Bullseye, but I just checked and the link I have no longer works. Nor does the booklet show up in a search of the Bullseye website, so it looks like they no longer carry it. But it may still be available from somewhere else if you get lucky.

Brad

Oh, thanks for the replies about viscosity. I didn't know. =)