Thermal Cracks weeks later??

[onesweetbead]

So I've noticed a very upsetting trend as of late. Beads that have been kiln annealed, off the mandrel and cleaned are suddenly appearing with thermal cracks vertically on them. This has happened with all types of colors and base colors. Today I reached in the bead basket to start stringing sets and a bead out of my favorite set EVER had developed 2 cracks vertically on each side literally overnight. As in I just looked at them last night while I was cleaning it and viola there it was today. These were made probably 1-1/2 to 2 weeks ago. When I run my fingernail over the bead I can't feel anything but its certainly there.

Thoughts?

[ditfd]

Can you provide any more details? Which glass? What colors?

Best,
Patti

[pam]

Also annealing schedule might be important.

[HWCGlass]

it happens.

i'll spare you my horror stories, but i have them.

i have this expression you might find useful, "follow the cracks, find the problem."

[Jasio]

Maybe pressing the beads too thin?

Andrea

[onesweetbead]

Thanks for the input so far. These are pretty chunky beads and none of them are pressed, just shaped lightly with a small dental tool. Its happened with green exotic (notorious for cracking when encased so I didn't pay much attention to those), pink, cherry strike, caramel luster, AP. Most of them were encased with clear, all had a white base, which I've used forever under colors with no problem.

I garage at 1050 and then when I'm kiln striking I ramp to 1100 and hold for 30 mins, then ramp down to 960 at 70/hour and hold for 30 mins.

I have no idea what's started happening but I'm paranoid about selling my beads since some of these are appearing a week or more after they're made and I have show coming up this weekend.

[PixieFireBeads]

I've had cracks show up in beads months later. I was encasing with Lauscha clear, since I stopped using Lauscha I haven't had this problem.

OOPS: I clicked this thread from the main forum and didn't realize it was in the boro room so my answer is probably not appropriate. I apologize!

[HWCGlass]

i say:

1) turn your kiln down. park it for a few days at an even 1000, see how that works for you; cycle your stuff the same, just hold down the temp wile you are working.

2) whose white? There is another thread around here about black; I went through this period of time years back where i thought that boro glass was like some sort of race relations symbol because nothing cracked for me like black or white. Until jade, that blew my thinking altogeather.

3) bead release?

4) how do you know they are thermal cracks? why are they not coefficient cracks? If they radiate from the center of the bead . . .

5) if they are cracking after you clean them . . . then they were reintroduced into the kiln? you heated them up a second time? Take close note to what happens on re-kilning glass.

6) Try smoking out of them, the cracks will 'fix themselves'.

[LyndaJ]

I've seen several threads that white next to the mandrel is prone to cracking later. Put down a small wrap of clear before the white.

Also, as for soft glass, make sure they have a good even heat before you garage them.

You can also probably put them back on a mandrel and reheat to heal the crack.

[HWCGlass]

Originally Posted by LyndaJ

. . . Put down a small wrap of clear before the white . . .

very smart.

[Kalera]

I would recommend borrowing a pyrometer and testing your kiln's temperature. I had a friend who went through this with soft glass for almost a year and was going nuts... it turned out that her kiln's temp was off by about 200 degrees, so her beads were simply not being annealed. Thermal cracks that appear days or weeks later are a red flag for kiln temp problems.

[dogsrlove]

Which "white" are you using?

Vanessa

[onesweetbead]

I've been using Star White, nothing changed there, but I did catch some threads about white cracking so I'll lay down a layer of clear from now on.

I'm starting to think the kiln itself might be the culprit. I had to replace the relay about 2 months ago, and everything seemed fine at first but I watched it run a cycle yesterday and it was bouncing as low as 1000 and as high as 1080 while it was supposed to be sitting at 1050. I don't know if this is normal for other kilns but its new on this one. I'm going to test it with a pyrometer this evening and find out if its even close on the temps.

These cracks look identical to thermal cracks, from the inside out. It was my understanding that coefficient cracks were more spider web-like, which is why I assumed it was something like a thermal crack instead. Once they are cleaned they are never reintroduced into the torch or the heat so its not happening under those circumstances.

Thanks for the input, I really appreciate it.