I've finally checked my beads with polarizing lenses and found that the ones I've batch annealed aren't properly annealed. I tried annealing them again and soaking longer, but it didn't help.
I ramp up slowly enough to avoid thermal shock, soak for 60 minutes at 520, then I ramp down 70 degrees/hour to 370. The odd thing is that I've use the same schedule (plus garaging at 520 while I'm working) when I anneal beads that I put directly in the kiln from the flame, and those beads don't show any stress. It's only the batch annealed ones that I made before I had a bead door on the kiln.
What parameters should I change first? Should I soak at a slightly higher temperature? Ramp down slower? Ramp down to a lower temp? How can there be a difference between the batch annealed beads and the ones I garage at once, if the temperatures and ramps are the same? :(
Now there's a question for you! Never heard of that problem before. I garage anneal, though (even if I don't have a bead door - erm).
Are the beads very big? I would try to soak a bit longer and ramp down slower (maybe 50 deg/hour - I know that number has been mentioned by someone experienced, just cannot remember which blog I read it on!)
They're small fairly round newbie beads. I didn't dare to make large beads when I was still cooling them in vermiculite.
Sorry I cannot help - I hope someone a lot more knowledgeable than me comes along!
My bead cube came programmed with a batch anneal schedule of
ramp up at 150 per hour to 520
hold at 520 for 90 mins
ramp down at 50 per hour to 250
turn off and leave to fully cool
Not a expert but if the beads are large it may be the soak time that is too short.
Hope you get an answer from an expert soon.
Nikki
not sure if this might help
http://www.frit-happens.co.uk/wiki/Annealing
After several rounds of experimenting I found that I have to bump up the temperature to 550 when I batch anneal beads. That's funny, because garaging and annealing beads at 520 works perfectly if I put the beads in the kiln right after they're made.
I even have photographic evidence (hope this works - the photos are on facebook):
Bead 1 cooled in vermiculite (not annealed):
(http://photos-a.ak.fbcdn.net/hphotos-ak-snc4/hs226.snc4/38641_140616859293060_100000342397143_270775_3464213_s.jpg)
Bead 2 garaged and annealed straight away (sorry for the bubble and other impurities, it was just a test bead to verify that my garaging+annealing actually works):
(http://photos-c.ak.fbcdn.net/hphotos-ak-ash2/hs106.ash2/38641_140616862626393_100000342397143_270776_209187_s.jpg)
Bead 1 again after batch annealing:
(http://photos-h.ak.fbcdn.net/hphotos-ak-snc4/hs164.snc4/37561_140783282609751_100000342397143_271619_2523126_s.jpg)
I was just about to ask for pics!
Bead 1 is clearly not annealed.
I can't see Bead 2 properly to tell whether there's any stress lines showing in that one.
Bead 3 is fine, it IS annealed, there are no stress lines visible.
Are you saying that Bead 2 isn't annealed properly? Do you have a better photo of that one?
interesting!
I think noora is showing that the bottom 2 are stress free whilst the top one is clearly not.
Bead 2 looks properly annealed, it was garaged + annealed at once rather than batch annealed. Here's a better photo of it. It has a big bubble in it, I didn't bother about quality when I made it since I only made it to verify that at least my garaging + annealing works. I was beginning to doubt it since batch annealing at the same temperature wasn't working.
(http://photos-g.ak.fbcdn.net/hphotos-ak-snc4/hs200.snc4/38355_140799675941445_100000342397143_271663_7638835_s.jpg)
The schedule I used when I finally got the batch anneal to work was:
1: 70 degrees/hour to 550
2: Hold 1:30 hours
3: Full to 520
4: Hold 30 minutes
5: 70 degrees/hour to 300
Then I let the kiln cool to below 50 before I opened it.
I've tried the same schedule but with a temperature of 540 at step 1. That did not anneal the beads even with a longer soak.
Steps 3 and 4 are probably not necessary, I was just too lazy to remove them when I edited the garaging + annealing schedule that I had used earlier the same day.
The ramp up in step 1 could probably be faster, I just took it slowly to be certain I wouldn't shock the bead.
My kiln is an Evenheat E360, very similar to Paragon SC2. The controller looks the same, except that Evenheat pre-programmed it with a whole bunch of useless PMC firing programmes and left only one fully programmable slot.
ETA: I'm now using 550 as my garaging temperature as well. If batch anneal doesn't work at lower temps, I don't feel secure using lower temps when garaging + annealing straight from the flame either.
Okay, could it be the glass you are using? Is it lauscha over silverglass?
Maybe your kiln is not reading a true temperature?
Be interesting to see how many others here use strain viewer or polarising filters to check beads as issue maybe more wide spread than just one person. Happen to me and I slowed down cooling rate which worked OK.
Ian
What type of polarising filter would you need to check this and are they expensive ?
Jenny
Quote from: Ian Pearson on July 28, 2010, 12:51:53 PM
Be interesting to see how many others here use strain viewer or polarising filters to check beads as issue maybe more wide spread than just one person. Happen to me and I slowed down cooling rate which worked OK.
Ian
I agree, it's so easy to think a schedule works because "it says so on the Internet" :)
Jenny, you really only need one polarizing filter (for example polarizing sunglasses or a polarizing camera filter) and a flat screen monitor (for example a laptop monitor or a flat screen computer monitor - the old fat CRT monitors won't do the trick). The flat screen monitor emits polarized light, so that you don't have to use two filters. You hold the bead between the polarizing filter and the monitor and turn the filter until it filters out all (or at least most of) the light from the screen. If all your own beads look okay, try it with some cheapo chinese lampies and you'll see the (actually quite pretty) stress marks :)
I guess the same as Mary, that my kiln doesn't read the proper temperature.
Beadysam, all the glass I'm using is plain old effetre, I don't have much else :)
Quote from: noora on July 28, 2010, 01:25:22 PM
Beadysam, all the glass I'm using is plain old effetre, I don't have much else :)
I just asked because, I recently had a sort out of my beads and randomly checked them with filters. The ones that were silver glass and Lauscha were stressed, but all the others were fine. Even on odd shaped ones you could see where the Lausch clear encasing touched the silver glass (or in some cases plain old effetre) and left areas of dark stresses. I won't be selling
those beads! Not that I ever get around to selling my beads anyway.... ::)
Quote from: beadysam on July 28, 2010, 02:44:45 PM
I just asked because, I recently had a sort out of my beads and randomly checked them with filters. The ones that were silver glass and Lauscha were stressed, but all the others were fine. Even on odd shaped ones you could see where the Lausch clear encasing touched the silver glass (or in some cases plain old effetre) and left areas of dark stresses. I won't be selling those beads! Not that I ever get around to selling my beads anyway.... ::)
Oh wow, that can be good to know! Maybe it's time to let go of the illusion that glasses with matching COE don't cause stress if properly annealed. Especially after my incident with a fused pendant made with Fuseworks COE 90 + Bullseye COE 90 that broke in the customer's purse :o I actually couldn't see any stress in the tack fused test piece I made afterward to see if there was compatibility problems, but a couple of weeks later the test piece had cracked too so obviously it wasn't fine either.
Now that I did an actual batch anneal (100 beads or so) the new schedule didn't work either >:( The stress marks are still there on the transparent beads. I'll give it one more try with an even higher temperature, then I'm giving up. It's just those ~100 newbie beads that I made before I got a kiln anyway. None of them are pretty enough to sell or give away anyway.