Cracking beads...

[Les]

Oh Har Har Tan....

[*rowanberry*]

I am going to change my annealing schedule to the one that Izzy posted on the other thread and see if it helps me, its slightly different to what I was using. Seeing as I have a habit of making huge beads, it may help.

wish me luck!

[Les]

Hope it works out for you Claire

[Dragonfire Glass]

It has suddenley got a bit colder weather wise the last few days. Maybe the beads are getting just that bit cooler than usual before going in the kiln?

[*rowanberry*]

actually you know.... i did change *something* on my annealing schedule in the batch that cracked - and that was the hold for garaging, which was set at just over 12hrs (I knew i was in for a long session!). Maybe it didnt like that being in the program and had a hissy fit at me!

(by the way any beads I am selling at the moment, are crack free and fully annealled as they were made a while ago!)

[*rowanberry*]

It has suddenley got a bit colder weather wise the last few days. Maybe the beads are getting just that bit cooler than usual before going in the kiln?

It could be that yeh, I guess - I am usually the opposite though - have too much of a habit of putting them in still glowing and they get fibre blanket bits on them! Oooops! When I work today I'll be very careful to make sure they havent cooled too much and twist them in the kiln and not place them down until the glows gone.

[Billie]

Good luck hun 

[♥♥Tan♥♥]

goodest of luck

[Dora]

Claire,

Found this thread whilst taking a break from the packing of my beads. I wish to mention that where you must be careful during cooling is the annealing region. This is the part which goes from the annealing point down to the strain point (380°C) - this is usually where stress can be trapped during cooling through this zone, so you have to go slowly. Perhaps as a guide, using a 1/2"/10cm  in diameter bead as a thumbrule (for larger beads, I do a longer slow cool):

Annealing dwell: 30min
Slow Cool: 5.38°C/min
Annealing point to Strain Point: 23.8min
Equilibrium dwell: 15 min
Final cool: 16.1min
Straining point to Room Temp: 33.7min

Of course the kiln will taking longer than those few mins to reach room temperature, though again I would like to stress here that you need to watch the ramping down from AP to SP (ie the Slow Cool or ramping down bit). After strain point has been reached and you let dwell for 15min, thereafter the stress is out of the bead and you can actually switch off the kiln totally if you like or have a firebrick kiln.

I personally don't shut off the kiln, since it's digital-controlled, I let the kiln run its full program. I also have used a e-control devise which measures how much electricity I used for the kiln and discovered that when the annealing program begins and somewhere along the way, the electricity is no longer drawn. The only thing I can't confirm is exactly when this happens as I didn't stand there to observe - what I mean here is you don't need to shut off the kiln if you have programmed it to run down to room temp, you are not drawing anymore electricity and not spending extra. With the program running its full course, you shouldn't need to worry too much about the beads cracking.

You have also observed yourself that you may have put in the beads too late and letting it cool too much where tension builds up on the bead. When I took my 1st workshop using the HH, I was told to put the bead into the vermiculite when it has lost its glow so that that the granules will not stick to the bead. When I finally got my kiln, I did exactly the same thing and most of the larger beads came out cracked as I put them in after the glowing has stopped. It's best to put the bead into the kiln while it's still glowing hot as long it is not in a soupy stage, that way you should eliminate your cracking problems.

Hope this helps.

[*rowanberry*]

Thanks Dora...

No cracked beads in the last few sessions!

I think the main culprit was the cold weather we had all of a sudden - and I was putting them in too late (my fear of the fibre blanket sticking was getting to me too much! LOL!). 

I think that was my problem to be honest - Now its warmed up and I've been careful all is okay again....

I was working with a fairly slow cool down anyway and long anneal (at least 1 hr) but have increased the anneal to 90mins and made the ramp down to strain point even longer (70c per hour) and increased the dwell at the strain point. I do a switch off after strain point bit, and it normally takes about 60 mins to get from 371 to room temp (sometimes more).

[♥♥Tan♥♥]

Yay Claire, I'm chuffed it's back on track for you