Large bubbles (1-inch plus) in my glass platter. Help with next project, please.
Posted: Mon Nov 09, 2015 11:43 am
I want to create a large 11-inch bowl. To learn, I'm using scraps from last year's snowflake project. I arranged 2-inch diamonds, half-inch sqares and diamonds, and 2-inch rectangles as tightly as I could. I filled the gaps with smaller shards and frit I was making on the fly. I arranged this in a rough 11-inch circle and put an 11-inch disc of Bullseye Tekta COE 90 on top. All glass is Bullseye COE 90, by the way.
Here's my firing schedule (from THIS SITE):
Ramp 1 - Rate/400, Temp/1000, Time/.20 (20 minutes)
Ramp 2 - Rate/400, Temp/1150, Time/.15 (15 minutes)
Ramp 3 - Rate/50, Temp/1250, Time/.20 (20 minutes)
Ramp 4 - Rate/850, Temp/1450, Time/.15 (15 minutes)
Ramp 5 - Rate/AFAP, Temp/950, Time/.60 (1 hour)
Ramp 6 - Rate/400, Temp/100, Time/0
I think the large bubbles are from escaping air from all the little pieces of glass. I think the Tekta melted very nicely and formed a perfect seal. I'm using a ceramic shelf in a Paragon 14-inch clamshell kiln that has wash painted on it rather thickly.
The bubbles had no bottoms and were just thin glass at the top. I've broken out the tops of the bubbles, placed some more scrap at the bottom, and used cut pieces of Tekta to cap. Plenty of room for air to escape this time. It's in the kiln right now cooling after last night's refire. I'll see what happens tonight.
FINALLY TO THE QUESTIONS!
1) How do I prevent this from happening in the future?
My thought is that since it was a full fuse of clear uncoated glass, that I could have cut the Tekta a few times to give the air a place to escape. Is this a sound approach?
2) My Christmas project is an 11-inch Poinsettia Round Texture Mold [LINK HERE]. What can I do to keep the large bubbles from forming when I place my cap glass on top of all the frit?
Here's my firing schedule (from THIS SITE):
Ramp 1 - Rate/400, Temp/1000, Time/.20 (20 minutes)
Ramp 2 - Rate/400, Temp/1150, Time/.15 (15 minutes)
Ramp 3 - Rate/50, Temp/1250, Time/.20 (20 minutes)
Ramp 4 - Rate/850, Temp/1450, Time/.15 (15 minutes)
Ramp 5 - Rate/AFAP, Temp/950, Time/.60 (1 hour)
Ramp 6 - Rate/400, Temp/100, Time/0
I think the large bubbles are from escaping air from all the little pieces of glass. I think the Tekta melted very nicely and formed a perfect seal. I'm using a ceramic shelf in a Paragon 14-inch clamshell kiln that has wash painted on it rather thickly.
The bubbles had no bottoms and were just thin glass at the top. I've broken out the tops of the bubbles, placed some more scrap at the bottom, and used cut pieces of Tekta to cap. Plenty of room for air to escape this time. It's in the kiln right now cooling after last night's refire. I'll see what happens tonight.
FINALLY TO THE QUESTIONS!
1) How do I prevent this from happening in the future?
My thought is that since it was a full fuse of clear uncoated glass, that I could have cut the Tekta a few times to give the air a place to escape. Is this a sound approach?
2) My Christmas project is an 11-inch Poinsettia Round Texture Mold [LINK HERE]. What can I do to keep the large bubbles from forming when I place my cap glass on top of all the frit?