The merits of making test beads

One of the first things I learned in lampworking is not to mix different COE’s because they are not compatible and in most cases it will lead to broken or cracked beads. There are some exceptions to this rule and under certain circumstances you can mix COE’s safely, but this should be done very carefully.

Quick side note: COE = coefficient of expansion. Glass expands and contracts with temperature. And different types of glass expand and contract at various temperatures because they use different ingredients. I personally use mostly COE 104 (= soft glass or soda lime glass), but occasionally also COE 96 and COE 90.

But even if you’re very careful not to mix the different COE’s, and stay only within one glass type, this doesn’t mean that you don’t have to deal with the one or other compatibility issue. Which I tend to forget sometimes. These are the days I’m banging my head against the wall saying “blech, I should have made some test beads”. Last week I had two days of head banging. Look at these cracked beauties:

The first picture at the top of the post shows beads with a base of Lauscha Black Cherry Red, decorated with the fabulous Taji opal frit (supplier: JetAge Studio) and encased with Double Helix Aether clear. Pretty, right? Except for those nasty incompatibility cracks that showed in the beads after I took them out of the kiln (some of those cracks appeared not right away, but within the next couple of days).

On paper these three glass colors should play nicely with each other – they’re all COE 104. Theoretically! So why are they not working? There could be a number of reasons but most likely it’s that one glass is at the upper end of the 104 COE spectrum, the other on the lower end.

This second pictures show some sparkle spacers that were part of a big set of beads. As a base I used Devardi Gold Aventurine rods, again encased in Aether clear. The same happened as with the red opal frit beads: Cracks appeared as soon as I started cleaning the beads. Another case of: should work, but didn’t.

Had I done test beads, I could have saved myself around 2.5 hours of work last week. And lots of frustration as well.

So why am I not doing test beads regularly? Good question. And every time something like the above happens I’m telling myself: that’s it Judith – from now on I will make test beads with every new glass combination before making a whole set of beads.
But then I’m sitting in front of the torch and look at my glass, see all the beautiful colors and possibilities and get ideas in my head. And off I go and get very excited and start making bead after bead after bead … LOL. All those pretty colors in my glass rack switch off the brain I guess!

But this time – this time I learned my lesson. That’s for sure! I mean it!
This time everything changes and I’ll make test beads with every new recipe!
Oh …. look at this lovely translucent turquoise.
I bet I could make a really great set if I combine it with this … and this …
Oh, and wouldn’t it be fabulous if I add a bit of this here ….
🙂 😉


4 responses to “The merits of making test beads

  1. i feel your pain judith! i have problems with one of my recipes and my mandrel material – technicaly it SHOULDN”T be a problem but it is, always, so i'm having to rework parts of my recipe ;P and god forbid you want to use glass from different manufacturers! then the finger pointing starts! sheesh! if you say it's 104 then it should work with all 104 – no backtracking and caveats! sheesh! i certainly understand how your glass starts talking to you at the bench ;)D

  2. I've had a few problems with compatibility cracking and learned 2 things: make the test beads at least as large as the beads you are planning to make for real and if in doubt, make them over a core of clear. I don't know why this helps but it does. Also, compaitibility is an individual issue. I may have an issue using the same glasses others have no problem with and vice versa.

  3. Carol, that's a very good point to make a larger test bead. If I make them at all, I tend to make them spacer size, just to see how the colors look like annealed or to see if a compatibility issue exists. But you're absolutely right, the size can make a difference. Also the amount of the different glass colors used in relation with each other. It's really best to make a test bead with the exact design & size that we have in mind.

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