have new evenheat GTS 2541 and am experiencing BIG BUBBLES

[Pam Kissel]

I have just started using my new evenheat GTS 2541-13. I have been fusing glass for three years with smaller kilns and never had such a problem I am having now. I have been doing test fires with Spectrum 96 and Bullseye 90 and am experiencing the same problem......you guessed it !!! Huge Big Blister Bubbles that pop and then form a hole. At first I thought it must be my kiln wash.....So I cleaned my shelves, and reapplied following the 1 to 5 ratio and firing in kiln for 10 minutes at 500 degrees. This has not helped. I then tried raising my shelves above the bottom heating elements as I thought this might be sealing the edges before the center is able to catch up. I also slooooooowwwwweeeeddd down my schedule to 350 to 1000, 60 to 1250 then 600 to 1425 or 1450 depending on the glass that I was using. This helped somewhat as I only got one big raise in the glass ( I wouldnt call it a full bubble) it did not pop but still is unacceptable. I have also lowered the top heating element to firing at 80% instead of 100%. I am making progress, but could sure use some brainstorming from you guys and gals as to any other possible solutions.

Thanks soooooo much my brothers and sisters in warm glass world!!!

[Brad Walker]

Most likely, your kiln shelves aren't flat. See what happens if you try a test with your old kiln shelf in the new kiln.

[Pam Kissel]

Thanks for the quick reply. I have placed a level on my shelves and they appear to be flat. I am assuming that is an accuate test.????

[Andrew]

I think Brad means the surface of the shelf may have dips. Leveling the shelf won't help if the shelf surface itself is not flat. Try your old shelf like Brad suggested or use fiber paper. I have a shelf that consistently gets bubbles unless I use fiber paper.

[Brad Walker]

Thanks for the quick reply. I have placed a level on my shelves and they appear to be flat. I am assuming that is an accuate test.????

No. First, because I'm referring to the actual surface of the shelves, not whether or not they are parallel to the floor. Second, because what happens at room temperature is not necessarily what happens at fusing temperature.

Try your old shelf in your new kiln and see what happens. Just place it on top of the new shelves.

[Pam Kissel]

OK tommorrow will be a new test fire with my old shelve. I think I will also make one with fiber board and try that. SSSHHHEEEESSSHH Thanks for your quick input. You know how it goes......I am not sleeping at night because my brain loves a good mystery!!!! I just dont like loosing all of the glass.............part of the price we all pay I suppose in order to keep learning!!!

THanks I will let you know my progress

[AVLucky]

I had the same problem when I first made the jump to a bigger kiln from a quickfire: Made up a really cool, detailed platter, popped it in, came back for a peek when it was at fusing temp, and was horrified to discover that it had turned into a sombrero! Fiber board or paper will definitely solve that problem, even the thinfire stuff, because it lets gases filter through and escape instead of being trapped under the glass and trying to find its own way out. As for the sombrero...I ended up breaking out the stretched part in the center and refiring it to get a big flat donut shape, and now it lives on as a "suncatcher" (a.k.a. interesting mistake) in my studio window.

[Ron Coleman]

I don't understand the need for all the speed between 1250 and full fuse. Slow down and let your glass conform to the shelf. Add a soak at 1225 or 1250 of about 20 min and then creep up to full fuse over about 45 min.

I swear I could fuse on a gravel road without bubbles. Just slow down and save your glass.

Ron

[Ron Coleman]

A little clarification about my previous post.

I think with rapid heating from 1250 to full fuse you're actually causing the shelf to warp. Looking at the kiln configuration tells me the shelves are probably seeing a lot of uneven heating. If the shelf is sitting on short posts there isn't any heat under it.

With side and top elements going full bore, and glass on the shelf there has to be a tremendous temperature differential between the edges of the shelf and the center. The result can be SHELF WARP.

Ron

[Pam Kissel]

Ron,

Thanks for the good info. I didnt get around to firing today, however am ready to go for tomorrow. I got very similar advice today from a good friend. She stated about the same as you, that I need to slow down, and that my glass is starting to lay flat around the edges but remainin cooler in the middle, thus the bubbles. I looked at my shelves and they are as flat as a pancake........(flatter) so I really do think that the problem is in the way that I am heating things up........makes sense that the selves would warp if heating unevenly and too rapidly.....I just got some 6" shelve post today and am going to use those tomorrow also. Ill let you know my results.......In the mean time I am learning a whole lot......


Thanks again,

[Tony Serviente]

Pam-I'm reluctant to believe that your shelves are warping, only because I regularly go from 1000 to target afap, with no bubble problems. While I accept the reasoning behind going slow around 11-1200, I get good results without doing that. I am guessing it is overfiring. You said it was a new kiln. Are you firing to schedules and temps based on your old one? If you are, that may be the problem. Since the glass reacts to a combination of time and temperature, even though you may be going to the same temp as your old kiln, you could be having a much slower ramp up, due to kilns wattage, construction, etc, effectively lowering the target temp you used to go to. I have five kilns, and three out of five need substantially different target temps to get the same result. The other two don't, only because I built them to be thermally identical. If this guess misses the mark, I would ask if you are using the new BE shelf paper. It is not porous like the old, and can cause bubble trouble.

[Pam Kissel]

Tony
Thanks for the info. I am currently firing my kiln. I am using a much slower ramp time. Yes I am finding that this larger kiln seems to hold a temp and fuses at a lower range than my smaller one. I really think that the size of the shelve has alot to do with it, as I am using two large shelves, am wondering if they heat evenly and how much heat they retain compared to the thermocupler temp reading. I dont have much of a science background, but am finding it all very interesting.

Thanks for your help

I will let all know how this fire comes out

[deborahbur]

I just got big bubbles for the first time. Got a new JenKen Oval 13. Fired at 400 to 1100, 250 to 1300, 1000 to 1490 hold 10. My 4x9 with clear BE and red BE on top were fine but my 8x8 same mix had a huge bubble in middle of all 3. I use BE shelf paper. Any idea?

Also, what can I fill my bubble holes with to make them cool looking??

Thanks
Deborah

[Tony Serviente]

Sounds like you are figuring it out Pam. The more mass in a kiln, the slower it will heat, so the shelves may be the culprit, but it could also be the ratio of wattage to cubic footage, as well as the kilns insulation. I would not worry about the shelves heating unevenly, as they all do to varying degrees. I work with this, when necessary, through adjusting schedules and cursing. Deborah-Check the archives for ideas on filling holes, there are lots of possibilities.

[Pam Kissel]

Deborah,

I dont know that I can offer much more than a shoulder to cry on. I am really trying to slow down the whole firing process. I am actually ramping 250 to 980, holding for 20 than 60 to 1285 holding for 20 than 250 to 1435. I am trying this with bullseye. I have discovered that this new kiln tends to actually run hotter than my small Jen ken. I would maybe try slowing things down and maybe go alittle slower when going from 1300 up to your full fuse. I have given up in trying to fill in the holes, at least until I have my problem figured out. Let me know if you have any success.

[Pam Kissel]

O.K. I am not quite ready to do a happy dance, but I am getting close.
Heres what I have discovered and what the final results are.

My shelves are flat.
My kiln is firing hotter than it thinks!!
my firing schedule yesterday was incredibly conservative:
250 dph to 980 soak for 20
60 dph to 1285 soak for 20
250 to 1435 soak for 10

I was using BE and had a full fuse at 1435!!

I fired an eight inch circle that.......praise the lord turned out beautifully!!
(slight happy dance)

I also fired next to the circle a 10 inch square that has two small (less than a quarter size) bubbles, coming from the underside. (no happy dance)

on the other shelve I fired a picture frame....turned out o.k. but full of devit, a small 4" square, wich turned out o.k. small bubble between glass, which I can live with.

I'm a thinkin that I should'nt have put both big pieces on the same shelve. perhaps separating them would have distributed the heat more evenly???????

I'm also a thinkin that when I soaked at 1285, my kiln was probably more than likely firing at around 3000, which would explain the devit.

I appreciate any and all comments........Its very helpful to brainstorm with everyone.......thanks so much!!!

[gone]

Hi Pam,

You should be able to fire as many projects as will fit on your shelves. I have the same kiln and found the heat not all that even, but have learned to live with the cool spots by using those areas to fire black glass, etc. The Bullseye tipsheet on "knowing your Kiln" is so helpful. It can help you determine your hot/cool areas as well as check the pyrometer accuracy.
Are you firing pieces that have areas with just one layer of glass? You're a lot less likely to get bubbles with 2 full layers.
Good Luck!

[Tony Serviente]

I'm also a thinkin that when I soaked at 1285, my kiln was probably more than likely firing at around 3000, which would explain the devit.

Pam-When you soak at 1285, assuming your thermocouple is accurate and well placed, you really are at 1285. Not sure what you mean by your kiln was firing at 3K(?), which would be a big league overfire. Don't forget that glass does what we want it to with a mixture of time and temperature. Two kilns going to the exact same temperature with the same glass and shelves can get two very different results, because one may heat more quickly than the other, so the glass gets to the same temp in less time, and less heat work is put into it. Conversely, a slow kiln puts more time into the glass on the way to target, and more heat work is done. The practical result of all this, is that fast kilns cook hotter than similarly sized slow kilns. It's great that you are keeping notes on this. When I get sloppy about my note taking, I end up reinventing the wheel and just making my glass suppliers and utility company happy.

[Pam Kissel]

Tony,
Thanks for the info and continued support!! I just noticed that you are from Ithaca. Are you connected with Corning Museum?? I love that place and hope to take some classes there in the future. I've never been to a more interesting museum, not just because I love glass either......my family humored me by coming with me and no one wanted to leave!!! Love Ithaca........Hope my daughter can attend Cornell someday!!!! (AHHHH a parents dream) I really just want her to attend somewhere where there is cool camping nearby..........of course so mom can visit!!
Thanks again for the info....things are certainly getting better. I just did not expect so much trial and error. Of course looking back, I dont know why I thought that!!!!
Have a great day