Annealing from a cold kiln question

BeadedChic · #1 2012-10-14, 6:16pm

If I need to re-anneal a bead still on the mandrel, what schedule do you use to ramp up the kiln to garaging temp? I have not done this before and am used to turning on the kiln, letting it ramp up at full speed to garaging and going to the torch.

I've read about putting the bead still on the mandrel into a cold kiln and doing your 'regular annealing schedule' but wasn't sure if the bead can take ramping up at full throttle or if there is a slower pace I need to program in to keep the bead from having too much stress (and cracking in the process).

Any help would be really appreciated...thanks!

wendbill · #2 2012-10-14, 6:29pm

It depends on the size of the bead. Is there any reason why the bead needs to stay on the mandrel?

AmorphousDesigns · #3 2012-10-14, 7:19pm

mine is set to ramp up over 2 hours (about 500 per hour).

Elizabeth Beads · #4 2012-10-14, 7:29pm

I ramp up full out and I make fairly big beads.

artsyuno · #5 2012-10-14, 9:37pm

So do I.

Angie09 · #6 2012-10-15, 6:05am

Quote:

Originally Posted by Elizabeth Beads

I ramp up full out and I make fairly big beads.

I hope this isn't a stupid question ... but would it be the same if she has NOT annealed the bead before?

Dale M. · #7 2012-10-15, 7:57am

If you want to risk losing some beads to thermal shock, just fast ramp them up ...

IF you want to preserve as many beads as possible and have more success the acceptable way is to ramp up slowly over a hour or two....

All I ever do is batch anneal and I always slow ramp up to annealing point (temp)...

Glass is a poor conductor of heat, and the enemy is excessive (fast) thermal expansion....

Dale

Molly Bird · #8 2012-10-15, 12:41pm

I accidentally left two beads on mandrells in the kiln & ramped it full blast when I made beads Saturday & they were both perfect. I was shocked.

BeadedChic · #9 2012-10-15, 4:52pm

Thank you everyone for responding...have not batch annealed before, so this is not a concept I am used to. I've been considering doing the low fire decals mentioned in another thread but didn't want to hijack that thread with questions about how to ramp up the kiln after applying the decals. Will try to slow ramp on some experimental beads first before I try it on the ones with decals....

ElizabethCreations · #10 2012-10-15, 5:03pm

Hi Donna,
I am actually doing high rampage on Large Straight Lentil focals for decals and I never had one bead that cracked or anything...

Have fun with the decals!

ewdb · #11 2012-10-16, 11:40am

i ramp up 350F/hr. with round beads you can probably take more risks and ramp faster since it will heat fairly evenly; with really big, thin, pressed and/or sculptural beads i'd be more conservative with the ramp schedule

Lyssa · #12 2012-10-16, 4:10pm

I've ramped up at full speed (0-925 in about 10 minutes) with beads as large as 1 inch across and not had any trouble, but I also know that one of these days I may lose a bead that way.

GabiLoraine · #13 2015-10-16, 9:47am

I'm actually going around reading annealing question posts because I had this same question.
I was doing demonstrations at a festival last weekend and made a bunch of tiiiiiny spacers which I left in a fiber blanket. I also left many on mandrels because one I pulled off cracked in my hand and I figure that taking them off the mandrels adds extra stress? No? So I left as many as I could on the mandrels and annealed in my regular working schedule which ramps up at full speed over like 15 minutes maybe... mainly because I was too lazy to change the schedule on my kiln.
So... I should re-anneal them, huh? I'm talking about beads that are smaller than half an inch diameter...

5betsy · #14 2015-10-16, 3:23pm

No need to reanneal. If I read your question correctly, you ramped up quickly then ran your usual anneal cycle. Right?

If so, you did fine and your tiny beads are annealed.

GabiLoraine · #15 2015-10-16, 9:27pm

Thank you! That's what I thought but I wonder, because then why would they tell you to ramp up for like 4 hours?

Otter's Flame · #16 2015-10-17, 2:54am

Gabi, ramping your kiln up to temperature does not really have anything to do with the annealing of your glass, so as you have already been told, there is no need to anneal them again provided your annealing schedule is correct.

The ramping up aspect of your kiln cycle does have to do with heating any room temperature glass you have in there possibly too fast. The faster it heats the faster it expands. A slow ramping up gives your glass the chance to heat up and expand in a more homogeneous manner. A rapid heating of glass can cause a piece of glass that may be under internal strain to heat unevenly and crack. Or, heating too fast can induce stress and then crack your glass.

With small beads like you have described it will be less of an issue. Larger pieces are more often subject to uneven heating and expanding therefore the reccommendation is to ramp your kiln up slower.

I tend to find many kiln cycle schedules run fairly conservative but that is usually a good thing. There are mathematical formulas available online and often from glass manufacturers that help you calculate a kiln schedule that is right for you. This is a good question, it promotes some great discussion.

Otter

Katia · #17 2015-10-17, 2:59pm

150C (300F or so) work for me for batch annealing. Yes, 3+ hours to annealing temp but no surprises so far.

GabiLoraine · #18 2015-10-22, 12:15am

Quote:

Originally Posted by Otter's Flame

...
With small beads like you have described it will be less of an issue. Larger pieces are more often subject to uneven heating and expanding therefore the reccommendation is to ramp your kiln up slower.

I tend to find many kiln cycle schedules run fairly conservative but that is usually a good thing. There are mathematical formulas available online and often from glass manufacturers that help you calculate a kiln schedule that is right for you. This is a good question, it promotes some great discussion.

Otter

Thank you for clarifying that! I knew these things, but I wasn't making the connections in my mind. This really helps a lot. I still haven't cleaned these beads so I might still have some surprises...