My long beads are cracking in the kiln?

Bunyip · #1 2006-12-07, 8:36am

I made two long beads, one a bicone, the other more of a tube, and both cracked on me in the kiln overnight. Very disappointing indeed. It looks like the ends are cracking, but the centers are fine (they're transparents so I can see the cracks pretty clearly).

I made these on double-dipped mandrels, using lauscha transparent clear which I overlaid with surface stripes of color. The beads were about 2.5 - 3inches (60-75mm) and the cracking happened in the areas with little to no decoration at the extreme ends. Now that I think back, one of the beads cracked while I was working it and I re-melted it back into place. I was very careful on the second one as a result of that and they went into the kiln hotter than I'd dare put them in a fiber blanket, that's for sure.

My theory is that I was too close to the end of the mandrel release? Is that a common problem? One cracked at the end of the mandrel, the other cracked very close to the mandrel edge of the mandrel release where the double dip transitioned to the metal. Does that set up huge stress in the glass? or am I missing something?

Thanks in advance for any assistance.

Glassgoodies · #2 2006-12-07, 8:50am

Actually it sounds more like you aren't keeping your ends warm enough. They probably had cracks already developing, but too small for you to see when you put them in the kiln.

Anastasia · #3 2006-12-07, 9:02am

That doesn´t sound like a bead release problem...but a heat problem.

Usually long beads tend to crack at the end....rarely in the middle, which means, you have to constantly keep the edges hot. Heat from the ends tends to wander to the middle...so if the bead is not too long, it actually is enough to keep most attention to the ends...and heat from the ends will keep the middle warm, too.
But the longer the bead the less it works. Which means, you have to keep the entire bead hot al the time...not only flashing it through the flame, but glowing red, since flashing it only touches the surface...and actually often makes it crack while working, because the layers of glass close to the mandrel got too cold.
I have 2 ways..one is the regular...the other is to turn the mandrel into the same direction as the flame goes...giving the bead a "bath" in the flame throughout its entire length.
At least...making long beads requires patience. Apply a little glass....heat the whole bead...apply glass...heat the whole bead...the bigger the bead gets, the longer it takes.
Some of my focal beads take 2 hrs to make...and most of it is building the bead and shaping.
Am I reasonably clear in explaning that?
If not, feel free to ask.
Anastasia

Bunyip · #4 2006-12-07, 10:02am

I actually got the ends on the second bead good and hot (almost runny) before putting it in the kiln. I had the whole bead glowing a nice shade of orange, but I think that the last heat I gave it was in the center. I'll definately be trying again this evening so we shall see! I'm not used to making long-arse beads so this is an exploration. The shaping is tough, as is the heat control, at least until it becomes a solid part of your skill set (which it's not... but I'm getting there).

Thanks for the responses, I can use all the tips I can get!

Bunyip · #5 2006-12-07, 12:45pm

Well the cracks on one of the beads wasn't as bad as it looked. Basically a small bit flaked off the very end. I wouldn't sell it but it's nice enough to decorate the studio or a pen or something...

You can see the area where it cracked above the hole.... and yes it needs to soak overnight and be cleaned again!

thanks for all the tips. Hopefully tonight I can have a success!