WarmGlass.com

I've been working on this bowl and got a huge bubble when trying to full fused some frit on it. I was hoping to slump it into this bowl mold.
Is it possible to just slump it into the bowl as it is? Seeing it, it feels like the bubble has just done some of the work so far but I'm very new to glass and especially bowls, and I'm aware that that's probably not the right way to do it. I've been told that I could drill a hole in the bubble and add frit (I'm unclear where or how to add the frit and what that would do) and fuse it again to let it sink back down but I'm getting that information 3rd hand and no one in the Makerspace I'm at has done this before.

I think I figured out why I got the bubble in the first place (there was a tiny air pocket underneath and I didn't bring it up slow enough) and have heard some good techniques for preventing it in the future but I'm hoping to still recover this piece. I know it'll look funky but I'd really still like to try and get it into a bowl.

Does anyone have any advice or guidance? Thanks in advance!

In general, it helps if you give us the firing schedule you used that caused the problem.

The bubble was likely caused by firing too fast between 1200 and your top temperature. If you share your schedule we can answer more definitively.

Slumping the piece won't fix the problem. And you can't fix it by just popping the bubble and adding frit. It's more complicated than that -- you need to flip it upside down and refire, then see what you have.

Schedule:
1. 300 to 500 for 30
2. 400 to 900 for 15
3. AFAP to 1425 for 30
4. AFAP to 930 for 40
5. 200 to 700, no hold then cool to room temp.

I figured that I brought it up too quickly; my iPad died and none of my notes from previous firings were backed up, so I was just using a schedule suggested by someone at the Makerspace I work at. But I changed the schedule for my next piece to one more similar to one that someone on Reddit suggested when I asked about this there and ended up getting another bubble in my next piece, too. I've never had a bubble before and then 2 in 2 pieces!

Here's the second piece: That schedule was
1. 300 to 1000 for 15
2. 400 to 1225 for 10
3. 350 to 1425 for 25
4. AFAP to 960 for 60
5. 100 to 700, no hold, then letting it cool to room temp.

Both pieces had Oceanside glass and Uroboros frit. I've bought fiber paper since then to put under my pieces to help with bubbles but I know my firing schedules aren't right either. I think I've figured out why I got the bubble in the first piece.
This is the other side and that red circle was, like, a mm higher than the rest of the glass, so it probably trapped some air.

For getting rid of the bubbles, you're saying to just turn it upside down and full fuse again? Do you have a suggestion for how to do that with the big bubble in a way that'll keep it from getting super wonky or is that just the way it'll be? Do you have a suggestion for a schedule for that?

Thank you for responding. You seem to have a lot of amazing knowledge and I really appreciate your help! And sorry for not answering you earlier! (I thought I'd get an email that someone had responded.)

Not long enough for a bubble hold. You need to hold at least 30 minutes at 1230F on the way up.

Too fast from the bubble hold to your top temperature. 200 dph at the most.

Too long a hold at the top temperature.

Lots of lousy schedules at Makerspace and Reddit.

As for refiring the damaged pieces, you can turn over and do a full fuse (but not following those two schedules). The piece may still look like crap, but the bubble should go away and be replaced with something else that may or may not be better.

Great! Thank you for the advice!

If I want the glass smoother, rather than more like a task fuse, how long do you recommend holding it at the top temp? Or is that more a matter of what the top temp is?

Yeah, I'm definitely finding that some people have bad schedules but hopefully I won't lose my records in the future so I don't need to ask people. I bought Kiln Schedules for Kilnformed Glass by Bob Leatherbarrow and I bought your book, so I'm hoping I can start to understand the science behind the temps a little better.

Thanks again!

Also, when I refire, I was thinking of putting fiber paper on the bottomto help with airflow around the piece. Can I put kiln paper (I have Bullseye Thinfire) on top of the fiber paper to try and mitigate the rough texture or would that defeat the purpose of the fiber paper? Is fiber paper something I should use for everything or just something good to use when I'm really invested in a piece? The person teaching me at the Makerspace (who does have, like, 30 years experience but has usually taught people projects that she then fires) has never mentioned using fiber paper for anything but lining molds.

BennettS wrote: ↑Mon Aug 11, 2025 3:19 am Also, when I refire, I was thinking of putting fiber paper on the bottomto help with airflow around the piece. Can I put kiln paper (I have Bullseye Thinfire) on top of the fiber paper to try and mitigate the rough texture or would that defeat the purpose of the fiber paper? Is fiber paper something I should use for everything or just something good to use when I'm really invested in a piece? The person teaching me at the Makerspace (who does have, like, 30 years experience but has usually taught people projects that she then fires) has never mentioned using fiber paper for anything but lining molds.

Putting fiber paper beneath your piece will stop the bubble issue, but if you fire properly you won't have the bubbles in the first place. So I wouldn't use fiber paper, I'd just adjust my schedule. The main time I would use fiber paper under a piece would be if I wanted the texture.

If you do use fiber paper, you can put thinfire over top, but that seems a waste of money to me.

BennettS wrote: ↑Sun Aug 10, 2025 10:34 pm If I want the glass smoother, rather than more like a task fuse, how long do you recommend holding it at the top temp? Or is that more a matter of what the top temp is?

The smartest thing to do is to keep the hold time the same and just vary the temperature. 10 minutes is a good standard to use. If you try to vary two things -- the temperature and the hold time -- you'll be confused as to which change gave you the result you want.

The exact top temperature will depend on lots of factors, including the color of glass, type of glass and construction of the piece. Best solution is to keep a log book of each firing and adjust based on what you learn. Every kiln fires differently -- we have seven kilns right now and each one requires a different top temperature to full fuse.

Yeah, I'm definitely finding that some people have bad schedules but hopefully I won't lose my records in the future so I don't need to ask people. I bought Kiln Schedules for Kilnformed Glass by Bob Leatherbarrow and I bought your book, so I'm hoping I can start to understand the science behind the temps a little better.

My book has a chapter on firing schedules that explains the basics. Bob's book is excellent as well. I would use those two as references, rather than Reddit or Facebook or similar sites.

I will definitely be consulting the books for figuring out firing schedules in the future!

Thanks so much for your help!