Layered fused pendant problem

[Kelly & Charlie MacMu]

Im trying to make a layered fused pendant aprox 1/2 " thick when done. problem is I can't get my glass from cracking on second firing. I usually have two layers that i'm putting on with my previously fused two layers.Im using dichoric and bullseye, it has to be with my heating and annealing process ? Also on one of my disasters the glass cracked and then slid off ? ( not a pretty sight!! ) I Would appreciate some ideas, suggestions?

Thank you,
Brand new to glass ( and I suck )

[Cher]

Hi Mac. Welcome the the wonderful world of warmglass. It's confusing and sometimes complicated doing anything new, so give us some more details. What kind of glass? Brands? overall size? The ramp speed and temps used?

[Carol B]

Im trying to make a layered fused pendant aprox 1/2 " thick when done. problem is I can't get my glass from cracking on second firing. I usually have two layers that i'm putting on with my previously fused two layers.Im using dichoric and bullseye, it has to be with my heating and annealing process ? Also on one of my disasters the glass cracked and then slid off ? ( not a pretty sight!! ) I Would appreciate some ideas, suggestions?

Thank you,
Brand new to glass ( and I suck )

What is your firing schedule for the second firing Mac? Do you have a picture of the fractured piece? That would be helpful in determining what is causing your fracture problems.

I am asuming the Dichro is the same COE as the BE glass.

[Kelly & Charlie MacMu]

Being new to this I hope ramp speed is how fast I turned my evenheat hot box kiln up to full fuse ? With second fuse per glass shop employee that I asked I started second firing at warm for about 10 minutes (350 degrees ) then medium ( 500-1000 degrees ) right at the beginning of this is when glass cracked and slid off then I just put it up to full fuse 1500 degrees for about 10 minutes it really didnt matter by then the piece was already hating life. The size of the piece is 1" wide and 3/8 inches thick (post fusing) I started with the piece that was already fused which consist of bullseye 1/8" on bottom dichoric scrap in middle and then the same bullseye 1/8" on top, then I added a piece of dichoric on the bottom ( thin ) and bullseye again aprox 1/8 inch thick on top. I need to apologize if my glass lingo is incorrect Sorry

Thanks,
Mac Trout

[Kitty]

your lingo is fine.
i like that part about the pendant hating life.
egad.

i think you have a lot of layers going on there. you might reconsider that, and if you are new to doing pendants, start with fewer layers, and work up to your thicker idea.

i also like to put a shelf of pendants in the kiln and warm them. my usual regimen is to heat the kiln to 500F over about 15 minutes. the kiln in question has side coils, and takes an 8" shelf -- it's a Cress enameling kiln, but works great for fusing. after 500F, i turn it on full and take it to 1490 or 1500 ASAP. but i must say, in the last month or two, i have started slowing down -- and this after six years of doing it the same way. the slower temp up around 1200 or so reduces spread of the pendant's shape, allows the top to flatten more, especially if i'm using up dichroic scraps from my earring production.

are you making these pendants with a welding rod inside them to form a channel, or fiber paper, or are they cabochons without a cast channel?

[Cher]

your lingo is fine.
i like that part about the pendant hating life.
egad.

ditto

[Lyn]

I fire in a small aim jewelry kiln and it full fuses in the back and tack fuses in front ( no elements in the door) I have stacked things 4 layers thick and never had things crack apart. For me its crucial where in the kiln things are placed.
LOW #4 to 500 20 to 30 min
MED. #8 to950 " " " "
HIGH to full fuse " " " "

My pyrometer is off 150 degrees, (I'm assuming), because it reads 1350-1375 when my pendants look full fused.
Peek in there and watch whats going on and keep experimenting.
This board is a great help to those of us that don't or can't get to classes for professional help! THANKS AGAIN CONTRIBUTORS
http://community.webshots.com/user/lynfeu
Lyn

[AVLucky]

Being new to this I hope ramp speed is how fast I turned my evenheat hot box kiln up to full fuse ? With second fuse per glass shop employee that I asked I started second firing at warm for about 10 minutes (350 degrees ) then medium ( 500-1000 degrees ) right at the beginning of this is when glass cracked and slid off then I just put it up to full fuse 1500 degrees for about 10 minutes it really didnt matter by then the piece was already hating life.

You'll probably want to get The Book at some point to help you along your way, or check the tutorials on this site in the meantime. Ramp speed is temperature over time. You can think of it like miles per hour in a car. At a ramp speed of 500 degrees per hour, you'd be at 250 degrees after half an hour, 500 degrees after one hour, 1000 degrees after 2 hours, etc. If 10 minutes on warm got the temp up to 350 degrees, that's 1450 degrees/hour if your room temp was 75. It's much more convenient to plan ramp speeds when you have a kiln with a brain (computerized controller) that will obey your commands. The hot box, on the other hand, will require some note-taking and tests for you to figure out how fast it heats at different levels on the dial. It's a matter of just getting to know your kiln. Take lots of notes. They always help, and can be pretty amusing later on down the road.

That said, it sounds like you thermal shocked your piece while it was heating up. (There's your speeding ticket. Artistic license, please ) Did you open the lid to peek in at that point? If you did, that might have contributed to the shocking. Generally speaking, (and I'm sure plenty of people here would be able to fine tune these numbers) it's best not to peek until you're at 1300 on heat-up, or between 1150-250 on cool down. Or did you only discover what had happened after it was too late? If the layers slid apart, they weren't fused yet, and you might have been able to salvage pieces of them if you turned off the kiln right away.

For something that thick, you need a slower firing time. I do small test batches in the hotbox fairly often, but usually pieces that are only 2 regular thicknesses or 3 thins. I have been able to heat them from room temp to fusing temp on high without any breakage, then drop to a lower setting to hold there for as long as I need. For regular firings I prefer a slower, more cautious schedule. Just because you can get away with something, it doesn't mean that it's the best way to go. Conservative schedules will probably give you better results.

Enjoy the journey, and remember that mistakes help you learn!

[Barbara Muth]

That said, it sounds like you thermal shocked your piece while it was heating up. (There's your speeding ticket. Artistic license, please ) Did you open the lid to peek in at that point? If you did, that might have contributed to the shocking. Generally speaking, (and I'm sure plenty of people here would be able to fine tune these numbers) it's best not to peek until you're at 1300 on heat-up, or between 1150-250 on cool down. Or did you only discover what had happened after it was too late? If the layers slid apart, they weren't fused yet, and you might have been able to salvage pieces of them if you turned off the kiln right away.

Just to clarify, thermal shock is most likely to happen when the glass is below 1000 degrees. I never open the kiln below 1000 on the way up or between 1000 and 250 on the way down. And I try to wait to open till the kiln is at 150 or lower.

Barbara