These BUBBLES are killing me!

[wendall]

I need help getting bubbles out of my fusings.

I take a piece of clear, cut out colored pieces, place them on the clear, and then cap it with another piece of clear. (Bullseye glass). So its three layers. I take it up to 1500 at 310/hour with a 15 minute soak. Now the bubbles have surfaced, but they don't pop. They pop to the touch after the piece is out of the kiln.

I have tried putting clear glass along edges to hold up the edges to allow air to escape, I've also tried holding at 1150 and then going up to temp. Nothing works!

I have a Jen-Ken kiln with the heating element in the top, with digital controller, so I don't think the kiln temp is the issue.

I'm thinking of bringing it up to 1700 this time.

[Steve Immerman]

If the bubbles are between the layers, than it is because you have constructed your piece in such a way that you are trapping air between the pieces. Try putting the colored design elements on top of the other two layers instead of inbetween. Make sure that your two layers of clear are 3mm, not 1.5mm, in thickness.

If the bubbles are between the kiln shelf and the glass, you may have an uneven kiln shelf. Lay a straight edge on it and see if it is perfectly flat. If not, you are trapping air between the shelf and the glass. Using fiber paper under the glass is a temporary fix for this. Getting a new shelf is the real solution.

Firing hotter will only make the problem worse if you are trapping air somewhere. 1500 for 10 or 15 minutes should be adequate for a full fuse.

Good luck.

Steve

[Dani]

Can you give us more info? Size of piece, kilnwash, fiber paper, or other, any glue used, etc.?

[wendall]

Thank you Steve, I never thought of putting the colors on top, I will try that now and see how the firing goes overnight.

(Dani the size of the piece is 9", and its firing in a 14.5" x 6.5" kiln. Each layer is the standard glass thickness.)

[Steve Immerman]

I hope it works. I my kiln, I would fire it to 1490 for about 15 min if I wanted the top design elements to blend into the piece. If I wanted to maintain a little 3D effect, I'd fire to 1480 for 10 min.

Steve

[Paul Housberg]

Putting your colored elements on the top layer as Steve suggested will help as well as using double rolled glass. However, you can successfully fire the colored elements in the center provided they fit together so as not to trap a lot of air.

Try this firing schedule: go as fast as possible—or as fast as you're comfortable—to 1250, soak at 1250 for 30 minutes, then go to 1480 at 600 degress per hour (still quite fast), hold for 10 minutes. If that works, try lowering the top temperature and/or raise the rate from 1250 to 1480 in order to arrive at the most economical firing. Obviously, all kilns are different, but I use approximately this schedule in three different kilns that I own for fusing three and four layers of glass similar to what you've described.

The soak at 1250 allows the glass to fuse slowly so that air can escape and lowering the top temperature prevents the bubbles that remain from breaking through the surface. You cannot avoid some bubbles with Bullseye, but they will be small and nicely formed. With Spectrum glass, you can virtually eliminate all the bubbles (which is its great advantage), however, I've found that Bullseye works better for subsequent hot slumps into stainless steel relief molds. (Not suggesting that one glass is better than the other - simply that I've had better results with Bullseye for the particular kind of work I do. And, I do like a few bubbles provided they're small and round.)

[wendall]

Thank you Paul, also very helpful. Right now, if I can get rid of those bubbles, I'll be ecstatic. But yes, the economics will come into question eventually. That was my next step, to figure out how fast I can reach certain temperatures without devit. Great tips.

Thanks again.

[Lorelei]

I found this thread interesting as I just fused two large circles with various pieces between them. I used Marty's schedule of ramping up to 1350 at 300dph. I ended up with a lot of large bubbles, *very* unattractive. I called the local WG shop and was advised to ramp up much faster because I was holding the glass too long around 1200. I understand that I need to have the centre drop before the sides in order to stop trapping air in there but now I'm confused with your reply where you say to hold it at 1250 for 30 min. Does this ensure the sides will drop slower than the centre?

[Dani]

Overspray will protect you from devit and worrying about holding temps in certain ranges too long, etc. I just use it on everything for insurance. Did you glue your pieces together? Is that causing the bubbles? Did you offer libations to the kiln gods? I want a bumper sticker that says "The Kiln Gods Must Be Crazy". My current solution for bubblevity is one-of-a-kind clocks. No need to drill a hole, it's already there. Don't get many bubbles these days.... must have taken all the fun out of it.

[Paul Housberg]

... I understand that I need to have the centre drop before the sides in order to stop trapping air in there but now I'm confused with your reply where you say to hold it at 1250 for 30 min. Does this ensure the sides will drop slower than the centre?

That's exactly right. Of course, there are many variables, your kiln, the manner in which you stack your glass, size of your piece etc. If you have voids in the interior layers, you may still get bubbles. You may find that holding at 1225, say, may work better, or going slower from 1250 to 1480, etc. If you have elements on the sides of your kiln and your glass is close you may need to baffle (although one of my kilns has side elements as well as top and I haven't had a problem).

I regularly fuse four layers of double rolled Bullseye glass roughly 6" x 12" The bottom two layers are clear pieces 6" x 12". The third and top layer consist of colored strips, 1/2" to 1" wide by 12" long placed side by side with no gaps. I fire about 25 of these per week using the schedule I described and I get very few bubbles. The bubbles I do get are small and round and don't break the surface. Not objectionable, in fact, I like a few bubbles.

Btw, I assume we're talking about bubbles forming within the glass, not underneath the glass. I use thinfire to avoid the latter. Also, double rolled definitely works better than standard Bullseye. Try some tests with scrap to begin. I can almost guarantee this will give you better results.

[wendall]

Hi Paul-

Yes, I was talking about bubbles forming in the glass in my original post (clear layer, colored layer, then clear layer on top). I'm going to try your firing suggestion today.

Last night I tried putting colored pieces on top, and they merged beautifully with no bubbles, except I hadn't yet refigured temp suggestions and went too high with the temp ... to 1675. Because of that I have kiln wash on the bottom of my plate.

I'll try some new pieces and go up to 1490. Hopefully the glass gods will bless my kiln today and I will not have to go mad!

[Paul Housberg]

Last night I tried putting colored pieces on top, and they merged beautifully with no bubbles...

I'll try some new pieces and go up to 1490. Hopefully the glass gods will bless my kiln today and I will not have to go mad!

Try 1480. Don't think you'll need to go higher. Also, depending on your design, you may get better results if your colored elements comprise, in fact, an interior layer. Maybe. I've found that sometimes colored elements placed on the top layer will pull away leaving a hairline of clear glass (the layer below) between them. So, there is some logic to trying to make it work with color on the interior. As with most things glass, it all depends...

[robertb]

My question is once you have the bubble (and you have the cure)can you save a piece with a nickle size bubble by drilling a hole in it?.If so do you drill through both layers or just the top layer? Which will leave you with less scarring?

[Lorelei]

On my piece that had the large bubbles, I drilled out the top of them, smashed up some of the same glass and filled the holes up. Did a re-fire and you'd never know I ever had bubbles!

[robertb]

On my piece that had the large bubbles, I drilled out the top of them, smashed up some of the same glass and filled the holes up. Did a re-fire and you'd never know I ever had bubbles!

Thanks Lorelei

[Lorelei]

hey! You're welcome!
do you have any idea how good it feels to ANSWER a question for a change!!

*rofl*

[Barbara Muth]

If you have elements all in the center of the circle, sandwiched between two layers then a slow soak at 1250 will cause the outside edges to slup down and seal in the air, unless you allow it a place to escape. That can be done using Brock's chad method. Place a small piece of glass, previously full fused so it is cabochon shaped, in several places sticking slightly over the edge of the piece. this alows the glass to slump down and squeeze most of the air ouyt the sides.

Another option I have used on occassion is to full fuse the elements into the bottom layer before firing on the top clear layer. It's smoother then and traps less air.

or you can stack the base, the design elements and then cover with a layer of clear 03 frit. The frit will let all of the air escape.

Good luck!
Barbara

[Lorelei]

Oh wow! Thanks a lot for that!

I'll try that tonight in my overnight firing!