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Boro Room -- For Boro-related tips, techniques, and questions. |
2006-09-17, 11:18am
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Join Date: Jul 11, 2005
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Thermal Cracking Grrrrrrr.
I took the summer off and I have been playing at the torch again but I am having a problem with lentil beads cracking on mandrels (3/32).
I don't know if its my kiln, the new mandrels or if I am just waiting a little bit longer to strike the beads in the flame. I had all but three lentil beads crack.
So, my question is:
Do you wait until the glow is off the bead as you look at the bead in the room or until the glow is off the bead as you look at it under the counter.
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2006-09-17, 12:08pm
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traumaqueen
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Join Date: Jun 27, 2005
Location: Utrecht, a town in The Netherlands, close to amsterdam
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you'll need to use a smaller size mandrell if you want to do lentils, the bigger mandrels are just too thick, too little glass around the mandrel so they will crack easily. You could also try to make your lentil thicker, or get yourself a chunky lentil press. This way there is more glass around the mandrel, and you won't have as many broken
Suzanne
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2006-09-17, 2:53pm
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Hey
I always use a 3/32" for my lentils, and use the largest of the 3. I wait until the glow is gone when looking under the table. I don't think it would be your new mandrels causing the cracking though. Any specific new color you're using that may be the cause?
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2006-09-17, 3:45pm
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Thanks to both of you for your help!
Suzanne I have always used 3/32 and not had a problem so its something I am doing that's messing the beads up.
Jen that's what is strange. I was using Star white and Aquatic Carnival for bases with twisties of black and AP. Then encasing.
I was wondering if my mandrels were made with a "new" steel that acted as a stronger heat sink. I tried one bead last night and it cracked also.
I think it has to be that I was waiting too long to strike. I made some test beads today striking a little sooner and I have my fingers crossed. I lost about two hours of work the last time!
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2006-09-17, 4:29pm
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Serenity Now!
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Join Date: Jul 15, 2005
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I think that what could very well be your culprit is if you've got your Star White touching the mandrel. I was having a similar problem, and found when I laid down some clear first before the white, the (cracking) problem magically disappeared!
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2006-09-17, 5:02pm
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I would think the same thing but its cracking with Aquatic Carnival and whatever black base I have been using also.
Fingers crossed! I made about 10 lentils and didn't let them cool as well. I also slowed my ramp sched. down just a tad.
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2006-09-17, 10:32pm
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traumaqueen
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Join Date: Jun 27, 2005
Location: Utrecht, a town in The Netherlands, close to amsterdam
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can't wait to see what comes out of this. I made a couple of lentils a while ago but they all cracked, then I switched to smaller mandrels and they were fine, but I can't remember what colors I used the first time, and I know I used different ones the second time.
Suzanne
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2006-09-18, 9:10am
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Jen
What is your annealing schedule? I think it is my annealing sched. I didn't let them lose the glow this time and they still cracked.
I still have cracked beads but about 1/2 cracked this time. ????
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2006-09-19, 4:44am
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Heidi (right?), I take it to whatever my striking temp is, hold, and bring it down to 1050 over an hour, and hold for at least a half hour, and have my kiln shut down from there. Make sure that your thermocoup is in enough, and your beads are at the back of the kiln.
That is so strange! Hmmmmm. Where did you get the mandrels from? The only thing I can think of is that your kiln temps aren't right for some reason or another...
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2006-09-19, 9:55am
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Thanks Jen for the advice.
The mandrels came from the welding supply.
My therocoup. was out about 3/8 of an inch (?) I guess that could have been what it was. I pushed it in before I annealed last night. Nothing cracked with this new schedule!
Yup its Heidi! I need to put that in my signature.
This is the schedule I used yesterday:
Ramped up to 1100 for 30 min
Down 60 degrees and hour to 960
960 Held for 45 minutes
Down 75 degrees an hour to 850
850 Held for 10 minutes
Down 150 hour to 600 then shut it off.
Its probably a little overkill but I didn't want to lose any to thermal shock. What a total waste of time!
Does anyone have any use for lentils cracked in half? I can't think of anything they would be good for.
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2006-09-19, 12:31pm
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Heidi, I'm glad nothing cracked! I bet it was the thermocouple (is that what the damn thing is called LOL?) Yes, your annealing schedule is way more than it needs to be, once you get the the 960 point, you should just be able to turn it off. Which type of kiln do you have?
Oh, and the cracked lentils...great for PMC...do you do any of that? If not, I'll take them and use them I hate cracking my beads apart. They're great for pendants and clasps!
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2006-09-19, 2:47pm
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I threw out a bunch of them but I still have about 10. PM me your address and I'll send the rest to you. Remember they are lentils cracked in half. So that makes the design on them weird. Really weird. lol
I thought it was called a pyrometer but then I have no idea.
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2006-09-19, 6:20pm
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Fire Goddess
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Join Date: Nov 17, 2005
Posts: 226
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I too, have had problems with cracking and am trying to find the common factor. I was wondering if Momka glass has less problems with incompatabilities and cracking. Does anybody know? It is great glass to work with , but I have very little .
CC
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2006-09-19, 8:53pm
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CC
I don't think its the glass in my case at all but my annealing schedule. The cracks are thermal and follow the mandrel, so I was either cooling them too long before striking them or the kiln was not cooling them slow enough.
I never heard or felt a ping and I thought it was the kiln.
Most all of the glasses are compatible. Momka has a lot of very nice colors. I just bought a few of her frits.
With boro you have to watch out for some of the greens and some glasses don't like to be overworked and/or overkilned. I haven't had a problem with greens. I back them with clear and use a thin coat.
What colors are you having problems with?
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2006-09-20, 8:18am
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Fire Goddess
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Join Date: Nov 17, 2005
Posts: 226
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Hi,
I had every bead crack with peacock chameleon and I had most beads crack with a bright yellow but I have all kinds of colors involved as dots and twisties. I am new with the boro and haven't figured it out. The crack is down the mandrel...I heat it all back up after I shape it. I wonder if my beads need to be farther back in the kiln. Some of the colors I had in a box were old, old, but the red was okay. It is an aggravation, but the boro glass is so gorgeous I am willing to put up with whatever obstacle there is, haha. More advice if you have it! Yeah, I love Momka, too. The color butterscotch is easy to work with....ughh.
Cher
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2006-09-20, 9:30am
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Cher
Did they crack in the kiln? If they cracked in the kiln then you need to bring them down to the stress point and hold them there for a while before ramping down further.
I haven't had peacock cham. crack but its silver added to peacock. On GA's site peacock's working tip says:
"Working characteristics: Work in a neutral flame. Do not garage in kiln at temperatures over 1090 and avoid extended garage times."
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2006-09-20, 11:14am
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Fire Goddess
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Join Date: Nov 17, 2005
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I have had them crack days later....I check them with a magnifying glass after I get them cleaned up. I had a beautiful set and lost 3 of them the next day. I have read the info on the GA site and have hard copy to refer to. I wish I had a photo, my hubby does on his computer of the set that had cracks the next day...when he comes home I will post so you can look at them, these had an avocado and pink base. I wonder if I put down butterscoth first and then that would be the glass touching the mandrel and it seems hardy, I could cover it with the colors and see if that works...watcha think?
Cher
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2006-09-20, 11:24am
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I haven't ever had problems with butterscotch but avocado is a green so I don't put that next to a mandrel.
What is your annealing schedule?
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2006-09-20, 11:43am
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Fire Goddess
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Join Date: Nov 17, 2005
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Yeah, I have heard about green, but some crack some don't, it is weird. I anneal different with different colors as prescribed, haha. It has to be me if peacock cham , (I did have stringers and all kinds of deco on it) didn't give you any trouble. I have tried pressing only once and heating back to hot hot and I have mashed and mashed and nothing seems to make a difference. Good grief I played with the Paramore colors and they don't mix with anything, gorgeous colors though.
C
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2006-09-21, 12:23am
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I think its your annealing schedule. When you bring down the temperature in your kiln you have to bring it down slow to the stress point then hold for a while depending on how big your beads/etc are.
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2006-09-21, 5:48am
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Fire Goddess
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Join Date: Nov 17, 2005
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I'll try changing the schedule. I also am putting the beads farther back in the kiln and none cracked last night, but I used red and it didn't crack last time. I found a yellow one that cracked since yesterday that was made over the weekend. I will take your appreciated advice and keep you posted on the outcome. Please do the same.
Cher
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2006-09-22, 12:17am
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Hi, not that I had something important to say about the cracking problem but I have an idea for half lentils:
mine were soft glass and made before I had a kiln, so I had really many of them....
Angela
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2006-09-22, 5:53am
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Fire Goddess
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Hey Angela!
Cool, I have some of mine on candles...it creates that colorful, what in the world is that look! Haha
Cher
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2006-09-22, 1:53pm
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Angela
Those are pretty cool! You definately made lemonade!
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2006-09-22, 3:21pm
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