Watered Down Bead Release and Cracking Beads

[Pat from Canvey]

If the bead release is too thin now, just leave the lid off for a whle until you like the new consistency. If your beads crack along the mandrel line at whatever stage, they are cooling too quickly. This type of crack is the result of thermal shock. Are you spending a little too much time working on the decoration of the focal and not keeping the core warm enough. Flashing the bead through the flame should be enough every few seconds to keep the whole warm then continue with the decoration. The beads may also be too large for the batch anneal process as the vermiculite or blanket allows the larger bead to cool too quickly. Larger beads need to be garaged. Even then, if you stop to admire the bead before popping in a kiln, it might still crack as it's cooled too much in the process.

[ejralph]

In my case, the beads cracked down the middle only because that was the line of lease resistance I think. It was definitely the bead release that was causing the cracks somehow. (Believe me, I went definitive scientist on the whole thing for two days!)

I have found that often incompatibility can also masquerade as thermal cracking. Much depends on the shape / type of bead. But for me at least, incompatibility on heavily encased round beads will invariably crack along the mandrel (often only on one side of the bead though!). If I heavily encase moretti in bullseye or vice-versa, I will always get my cracks running along the mandrel.

With thinly encased beads or beads where the glass is all mixed up in different ways, the incompatibility shows in more traditional random crazing or J-shaped cracks running around the bead in the case of the thinly encased stuff.

I only say all that, because i think sometimes incompatibility issues are often wrongly dismissed as thermal issues and cracking along the mandrel isn't always definitely thermal.

I think the bead-release issue is thermal related though, in some shape or form, as to how much it insulates the mandrel maybe. All very odd.

It would be interested to test it out by double-dipping with the same release, or using it thicker and seeing if the cracking beads still occur?

Emma

[Trudi]

I only say all that, because i think sometimes incompatibility issues are often wrongly dismissed as thermal issues and cracking along the mandrel isn't always definitely thermal.

I've heard this too - I had a problem with some Bullseye glass - a yellow that was encased with clear and shaped as a lentil. I've made loads that were fine and two made the same way cracked (all the glass was BE BTW) sometimes certain colours don't like to be encased!

[Redhotsal]

I have been having the same problem with my focals, they are all fine until I take them off the mandrels, I also batch anneal and they are fine when I take them off, but crack later,  and they are the best ones that I have done - I'm gutted.  How do you 'heal' them please?
Sue

You can heal them easier if you have them left on the mandrel. It is possible to ramp up a cracked bead in the kiln (on its mandrel). Get it up to 520 C and let it soak at that temperature for about an hour. Take it out of the kiln and introduce it gently to the top of the flame. You can then gradually get enough heat back into it to fuse it back together. You will lose surface decoration like bobbles or raised stringer as you'll have to melt them into the surface but it can be useful especially on larger beads that have taken a long time to make.

This is not an easy technique if you've already taken the bead off the mandrel and obviously doesn't really work out for those who are batch annealing.

In my experience I have had cracked beads when the bead release has been too thick but never too thin. Sounds like your beads are shocking before they hit the vermiculite or maybe there's a problem with the vermiculite. I once had a spate of cracking beads because the vermiculite was actually damp.

[suzanneC]

Thanks Redhotsal, I did begin to wonder about the vermiculite as they were quite big beads, I think I shall probably not try to batch anneal - especially focals and put them straight in the kiln (nearly typed bin then), it's just been one of those weeks.
Sue