I've progressed from fusing bubbles to slumping bubbles. I have been having center bubbles in BE 14 1/2 square mold. White was fine, black was worst. 300dph to 1100.afap1350, hld 15 to 20.
Should I slow between 1100 amd 1300?. Additional refire didn't help, retry on black a disaster.
Would raising mold up a bit from shelf help air escape?
I'm starting a new speciatly section for an upcoming show-Perforated Art
Jeri, holier then ....
Does the mold have small holes in the bottom? It probably should if it doesn't. Yes, elevate it slightly above the shelf with kiln furniture being careful not to block the holes (and make sure kiln wash isn't clogging holes either). Then check to see if it's level and adjust so it is.
I don't slump higher than 1150. I usually put a 20 min hold in around 1100F, then 300 dph up to 1150 with a 30 min hold there. But most of the time I stop the slump well before then and go afap to annealing ramp.
1) Make sure the air holes in your mold are not plugged with kiln wash.
2) Depending on the shape of your mold raising it off the shelf with some kiln furniture or pieces of fiber paper will help the air escape. Is the mold sitting on the shelf so that the air holes are blocked on the bottom? Does the mold have solid sides that prevent air from escaping from inside the bottom edges? (Just make sure the mold remains level and well supported).
3) Going as fast as possible from 1100 to 1300 is probably too fast and too high for slumping. Have a soak of 15 min at 1100 or 1150. You want the glass to be evenly heated before it starts moving. Peek at the piece. Then inch the temperature up 25 degrees. Hold again. Once the glass starts slumping hold that temperature until it is done.
The lower the temperature you use for slumping the more even the slump will be, the glass will stretch more equally and you will have fewer mold marks on the bottom.
Hope this helps. I had my own bubble experience this weekend. I blew two big bubbles in two pieces fusing on Friday night from using a kiln shelf that obviously wasn't dry enough. Bummer!
Thank you for the advice. Still getting schedules together.
there are holes in mold and I added a few more( can air come up as well, I guess so) The mold center does not touch kiln shelf but all sides are flush. I will try to notch some of the sides
I will definitely slow down
Thanks again
I wouldn't necessarily put notches into the sides of your mold. That might weaken the structure.
You could insert a piece of fiber paper under each side - raise it just a fraction of an inch off the shelf - enough to let air escape - but keep it level.
I would agree with the slower, but also advise lower. Depending on the depth of the slump and the thickness of the glass, you should be able to slump the piece at 1225-1250 probably with the same 30 minute (or less) soak.
Hi,
I have recently started using Bullseye's schedule [with slight modifications] for slumping as found on the back of their Ceramic Slumping Mold bulletin with much success.
I use 500 to 1250 and hold for 5-7 minutes for shallow molds and up to 30 minutes for steeper molds.
Then full throttle to 960 and anneal for 40 minutes
I've progressed from fusing bubbles to slumping bubbles. I have been having center bubbles in BE 14 1/2 square mold. White was fine, black was worst. 300dph to 1100.afap1350, hld 15 to 20. 