Big Fat Air Bubble

[Amber]

What can I do? I've got a problem with big fat air bubbles coming out when the local shop fuses things for me that are large. This one piece that I set up the other day and left for fusing is a 12" round scallop edge bowl. I laid a full piece of white glass over top a piece of clear glass, then did a simple shaded cherry design smack in the middle. After doing some reading online I left instructions for it to be soaked at 1150 for half and hour, what the booklet they had suggested was 1100 for 25 minutes which is what they did. They haven't slumped it yet, just a contour fuse with the soak, is there anything I can do at this point to remedy the bubble problem?

[Anne]

Becki is probably the best one for advice on this one Amber.  I have an idea what to do but I'll wait for her to tell us - she's the expert here! --------or Kev?

[Kev]

Sounds like my forth of July experience. It's trapped air or moisture between the layers. or moisture between the shelf and the glass. What I do now is preheat the kiln to 700 degrees and then cool it off to remove any moisture in kiln shelves or firebrick may have absorbed, before I fire....or course if your using someone elses kiln, that's harder to control. Another problem might have been that it was also ramped up too fast and the edges sealed before the air/moisture  had a chance to escape from between the layers. My friend Becki would say....slow it down.....,,she will be along soon and can be more specific, as I am on the learning curve as well.

[Becki]

Does it look like the bubbles are between the layers or from underneath? Your set up makes me think that they're coming from under the glass.  Do you know if she fires on a kiln washed shelf or shelf paper? Do you know the entire schedule?  Is the shelf smooth and flat?  A number of things can cause bubbles to form. Do you have a picture?

Any moisture should burn out before it causes a problem. I'm thinking it might be the shelf or the schedule.

[Amber]

They are using the paper, and they had an issue before with leveling but I just asked him on the phone and they are sure it's been fixed since then. This is what he fired at for a schedule:

 ramp 325 to 1100
       hold for 25min
 ramp 325 to 1550
       hold for 20min
 ramp 600 to 1440
       hold for 5min
 ramp down to 950 (they said infinity 999?)
       hold for 40min
 ramp down 150 to 800
       hold for 10min
 ramp down (shut off, infinity 999)
 



I haven't actually seen the piece so I can't describe exactly what it looks like or shot pics, they called me on the phone after it was fired because I was in a couple days ago and expressed concern over the firing. I'd gotten a piece back with fat bubbles in the past and I know sometimes they fire a bunch of different stuff at the same time even if they need different schedule so I wanted to talk specifics about this piece and asked for a soaker time since I knew it was a risk for bubbles. I've looked inside the kiln lots and the shelves are smooth and flat, clean etc.

[Becki]

I don't think your set up had a risk for bubbles unless you had glass between the layers. The problem with firing alot of different projects at once is that, unless they're approximately the same size and set up, one schedule may not work for all. His schedule is a bit strange.  1550 is high for only getting a contour fuse. Are you using BE glass?  I rarely ramp up faster than 300, usually slower. I wonder if other pieces are getting bubbles too?

You may be able to flip the piece over and refire but I don't want to recommend that without knowing why the bubbles formed and how big they are.  Have they offered you a solution?  It seems to me if they fire glass frequently they should know what's causing it and a possible solution for fixing it.

[Amber]

I thought firing various things all at once was a it off and that's why I talked about soaking times and what not, it can have panels to slumped votives to bowls and after spending X amount on the glass I didn't want another bad bowl. I'm pretty sure the bump is between the two sheets of glass, so the underside is flat and the top is with bubble bumps. Most glass is Uroboros, frit and noodles the same, sometimes some spectrum system 96 glass too.
They don't have a solution, a phone call from them telling me the problem and I said I'd look into on my end to see if something can be salvaged. The first batches of bowls they did, for themselves, they didn't use a clear base of glass so they didn't run into the problem, I like the weight of two layers of glass though and I'm not really looking to that ditch in favor of no bubbles, since I know it can be done. It just bugs me to buy the glass from them for this bowl (10.95 for the clear sheet and 14.95 for the white plus 5.00 firing feel plus taxes) and in the end it's bumpy from bubbles and I wasted my money.

[Becki]

Firing one layer of glass will not guarantee that you won't get bubbles and if taken to full fuse temp can cause a whole new set of problems!  The man needs to stop firing anyone's glass until he gets a clue! System 96 (and Uro 96) full fuses at 1465.  He's not even taking that into consideration! I could go on but it makes me so mad I could spit!

You said that they were bubbly bumps...are they really just bumps?  If so you may be able to get away with flipping it over and firing it face down then flipping it and firing polishing. You'll lose any dimension you have but it might take care of the bumps.  I know that's 2 more firings but it's no good to you the way it is and if he slumps it you'll just have a bumpy bowl.  I'd really be leery of letting this guy handle it unless he learns to adjust his schedules.  Is there another shop that could possibly do it for you? 

[Amber]

I don't have anywhere else to go and even though I've been looking online kijiji (kinda like craig's list) for a used pottery kiln but nothing is coming up for a good price. I see one for 50 bucks  "working order" but it's so cheap and old that it's a red flag. I think I'm going to hop off the fusing band wagon, it's been a trip but I'm just not able to afford even small wastes in glass. I'll save my pennies as I can and buy a machine down the road.

As for this bowl I think it's likely air bubbles that I'm seeing but how can I tell the difference and what else could it be? I'm thinking of trying to flip it over like you say, could I bother you for any firing temp/time suggestions? And will the small cherry design I did on the front with frit turn bad by flipping it?

[Becki]

They're all air bubbles...some come from between the layers, some from underneath. You can still have a flat bottom and have bumps.  They can sometimes be fired face down and flattened out.  It will flatten your frit out also and your design will have a matte finish if it's not flipped again and fire polished.  Some bubbles (usually the ones between the glass) thin out as they grow. There is really no fix for these.  Some people break the bubbles and fill with clear frit before refiring but it will always be noticeable.

Save your pennies, girl, and get your own kiln!  You'll be so glad you did.  I know it's a big expense but think of all the money you'll save not having to go to someone that's clueless and having him ruin your glass!  Who the heck can afford that??

[Amber]

I looked at another bad bowl and the bubbles are definitely coming from the bottom, not between like I thought. I had hoped to keep the shape of the cherries but I'll take flat berries to a wasted bowl *lol. I'm gonna go the flipping and then finish with a fire polish and call it a day with his kiln. I'll keep putting money aside as I go along and then buy my own kiln, it may take 6 months to a year with all the other silly things like table, coverings, bags etc that are on my list but it's better for me in the long run I think. It stings to much to worry about wasting even a few dollars here and there on badly fused glassware.

[Becki]

I wish we lived closer...I'd share!  I sent you a pm.  I hope it helps!

[Audrey]

Just be patient. Save your money and you will stumble across just what you need when you least expect it.

[ct4mom]

Yes Amber when you least expect it it will happen like mine. If I hear of any deals I will pass them along. Even if you have to travel a bit might be cheaper than shipping..

[Anne]

and Amber, our Canadian $ is getting better.  I'd save your $, keep watching Kijjii etc and who knows maybe you'll be able to buy a new one.  But, I would recommend whatever you do buy if you have to save a little longer buy, a bigger one.  I have a hotshot and while it's a great kiln I really wish I'd gone bigger.

[Amber]

You read my thoughts Anne *lol, about a month ago I was scouring around about kilns and the hot shot was the only one that was priced low but I just knew it wasn't for me. For the sake of having something soon, and I know I'd use it and love it to bits ;), I would just be needing a bigger one sooner rather then later. I'm willing to buy used within a certain driving radius (total driving time 4-5 hours) but if I buy new then likely I'll have to go to Halifax. For now it's kijiji :).

[JoanFrances]

Amber, I don't know what your budget is but Y glass has 1 Skutt kilns on sale that are bigger than the hot shot.

Skutt-Studio Kiln  $545.95    and    Skutt-Hot Start Pro  $648.88

[Amber]

The only thing with ordering from YGlass is the shipping fees, it's just too much. Even the kokomo box I bought from them a while ago was 150.00 in shipping and the only reason I did it was even with that stacked on the glass came out to 7.14 a square foot in the sale so it was worth it. To ship a kiln here from the states would be big bucks :(.

[Becki]

I agree, Amber.  Shipping within the US is bad enough!  The 2 kilns that Joan mentioned are the same size as a Hot Shot...if you want bigger, go for it!  You'll get there!  You might even look into square kilns...alot less wasted space.

[JoanFrances]

I agree, Amber.  Shipping within the US is bad enough!  The 2 kilns that Joan mentioned are the same size as a Hot Shot...if you want bigger, go for it!  You'll get there!  You might even look into square kilns...alot less wasted space.

SOOOOO sorry!... I put the wrong name in.  I confused the hot box and not hot shot. 

[Stephen Richard]

They are using the paper, and they had an issue before with leveling but I just asked him on the phone and they are sure it's been fixed since then. This is what he fired at for a schedule:

 ramp 325 to 1100
       hold for 25min
 ramp 325 to 1550
       hold for 20min

What glass are you firing? 842C is far too high for anything other than float.

 ramp 600 to 1440
       hold for 5min

What ever is a soak at 781C on the way down for?

 ramp down to 950 (they said infinity 999?)
       hold for 40min
 ramp down 150 to 800
       hold for 10min
 ramp down (shut off, infinity 999)
 

There is no bubble squeeze in that schedule.  It would be around 1200 - 1250F for Bullseye, maybe 1330F for float.

I think you need to get more control over the firing process.  Perhaps you should make enough to fill the kiln so you can determine the firing.

[Anne]

Amber's using Uro and Sys 96 Steve.  What schedule should she have used? Neither she nor I know what you mean by bubble squeeze - we need the schedule!

[Becki]

A bubble squeeze is a slow ramp segment added to your schedule to allow the air between the 2 layers of glass to slowly be pushed out before the glass seals together.  There are varied approaches to a bubble squeeze....some just soak at slumping temperatures, as Stephen obviously does, and some combine a slow ramp up with soaks through the slump temps.  I don't always use a bubble squeeze in my schedule but when I do I  ramp up slowly (50-75dph) between 1050 and 1250, a method I learned from another artist, Barbara Muth. It works well for me.

I'm not sure if I even brought up a bubble squeeze because the piece had already been fired...once the bubbles are there the squeeze will do no good.

[Stephen Richard]

Amber's using Uro and Sys 96 Steve.  What schedule should she have used? Neither she nor I know what you mean by bubble squeeze - we need the schedule!

With sincere respect you do not need a schedule.  You need the information to be able to construct a schedule.  You will see Becki has given the explanation of a bubble squeeze. 

the reason that I say you do not need a schedule is that many think a schedule tells them all they need to know.  Unfortunately, using someone else's schedule can only lead to questions down the line.   It is important to know the princilples rather than the schedule.  the principles can help you to build schedules to fit a variety of circumstances, but schedules alone are suitable for only a single kind of application.

Uroboros and S96 use different temperature points and firing strategies for their products.  If you look at their sites you will find the schedules they recommend for general purposes.

Steve