- December 7, 2011 at 7:57 pm #9722
After doing a full fuse sometimes my glass pieces have small pinpoint-sized pits in the surface. What might be causing these and how can I remedy the situation?December 7, 2011 at 8:08 pm #12332
These pits are bubbles that have risen to the surface and burst. Most glass has small seeds (or bubbles ) in it. These – when the top temperature is high enough or the soak long enough – rise to the surface and burst leaving a tiny “hole”.
The remedy is to fire slower and lower.
Stephen RichardDecember 7, 2011 at 8:19 pm #12333
Which segment should be slower/lower?
Will refiring smooth out the surface?December 7, 2011 at 10:46 pm #12334
“Which segment should be slower/lower?”
hard to say as no information on your firing schedule is available.
Possibly. It is also possible that you will reveal other bubbles.
Sharing some information about your firing schedules, your firing conditions, your layup, your kind of kiln (side or top fired for example), will help people give you appropriate advice. Was the information in the glass tips blog any use?
Stephen RichardDecember 8, 2011 at 5:33 pm #12335
I’m firing two layers of 3mm glass; clear on the bottom, opal and/or streaky on top (I don’t seem to notice any pits when firing with some of the transparent glasses – perhaps they are just harder to see). My kiln is a Skutt Box 14, with the elements in the top. The fusing schedule I’m using is as follows:
400/hr to 1150
150/hr to 1250, hold for 60 minutes
400/hr to 1465, hold for 20 minutes
AFAP to 960, hold for 60 minutes
150/hr to 700, shutoff
I’m considering changing the rate on the second segment to 100/hr…December 9, 2011 at 8:41 am #12336
I have often found that I get the best results with opals, by putting the clear on top. I have occasionally had bubles from the clear base rise to the top, leaving clear pin-points within the opal colour. I also have fewer problems with devitrification when the clear is on top. So clear above opal is now my practice.
I do my bubble squeeze differently – not that your method is wrong – lots of people do it your way.
I soak at 677C for 30mins for a 6mm project. Having done a slow rise to 677C, you do not need a whole hour there.
Depending on your desired surface, you might thnik about raising your 796C top temperature to 804C but hold for only 10 minutes. This should give you an almost flat surface.
I don’t remember whether you are using Bullseye or System 96. In either case you can do your annealing soak at 482C for an hour. Then to 427C at 60C/hr. Follow this by 120C/hr to 370C. If the piece is 6mm you can turn the kiln off then, but I normally control my cooling all the way down to 100C.
In short, I think you will eliminate your bubble problem by putting the clear on top and reducing the amount of time at the top temperature.
Stephen RichardJanuary 28, 2012 at 6:38 pm #12337josthingsParticipant
I bought a glass pack in some beautiful colors but it had a lot of seeds in it, so I fused everything upside down, all the bubbles went to the back pice of glass and dissapated, after I cold worked I slumped it right side up and thye all turned out really well. So I know do this with anything that looks like it might want to bubble.
I have also done this with pieces that had bubbles show up out of nowhere, I simply flip it over and full fuse again. It does not work on all bubbles but they do seem to head for the back so that the top is smoth.
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