BIG bubbles!

[Julieann]

I know this has been discussed before. I'm just starting out, and I've been using this forum as a guide to any problems I've had. I had problems with small bubbles right at first and then looked it up here. Found out I needed to slow down the ramp to temperature. That really worked nice!

However, all of a sudden they are back! Big huge, size of coins bubbles! I'm using this firing schedule:

400 dph to 1000, hold for 15 min., 200 dph to 1350, hold for 20 min, 125 dph to 1475, hold for 1 hr, AFAC to 960, hold for 45 min.

I don't understand how it can have worked so well for several firings, and then these last two firings I'm having big bubble problem again. I should mention that it appears from the spreading of the glass that it almost looks like the kiln was at a higher temperature????

Very wierd.

Anyway, if anyone has any suggestions, they would be greatly appreciated. I guess I'll go pop the bubbles and fill them with frit now....

Julieann

[Phil Hoppes]

A couple of observations. My first guess on the bubbles is that it is coming from your shelves. You did not mention the size or type of kiln but I'm guessing you are using mullite shelves. (These are the heavy, ceramic tile like shelves) This type of shelf is notorious for causing bubbles. A few things to look for right from the start. Get yourself a good metal ruler, yard stick preferably, and place it with the small flat edge you use to measure with down on the shelf. Now get your eye level with the top of the shelf and look under the ruler. If you see daylight under the ruler, you will now see the high and low spots on your shelf. If you have multiple shelves, look at all of them to check them for flatness.
If they are not totally flat, the low spots will cause a bubble if it is trapped under the glass. For uneven shelves there a few things you can do to fix the situation.

1) Drill small holes in the low spots (1/16"). I really don't like this solution myself as at fusing temps you will see the hole's mirrored in the bottom of your work.

2) Use a shelf paper. You can use either thinfire from BE or Brad Walker sells a very good shelf paper from the board. I believe he calls it J110. Check the classifieds.

3) You can grind the shelf flat using a silicon carbide grit such as that used
for sandblasting. Get yourself a ceramic tile (saltiel....I know I'm spelling this wrong...) this is the type of red clay ceramic tile you find in hardware stores that does not have a glaze finish. You use the tile as a tool to grind the top of your shelf with the grit and water inbetween. This takes a LOT of elbow grease so if the shelf is way out of flatness you will be grinding a long time.

Another source of your bubbles may be that you did not dry your kilnwash sufficiently. When I kiln wash a shelf, I put it in my kilns for and hour at 500 with the kiln well vented. This guarantees a dry shelf for firing. If you live in a humid climate and you store your kiln shelves for days before firing them you may need to dry them again before you use them.

Another way to rid yourself of bubbles (this is what I did. I had the same problem) is go away from mullite shelves and use rigidized fiberboard as a kiln shelf. These are lighter and easier to work with. They have some downsides too but all in all I prefer it to mullite shelves. If you are interested, send me an email and I will tell you how to get them and prep them for use.

Hope this helps,

Phil

PS - Your schedule is fairly conservative on ramp up. This is fine but I'm curious as to the thickness of the piece you are firing with this schedule.

[Steve Immerman]

Of course Phil's suggestions are right on target.

If the shelf is the culpret (as I suspect it is) you could just get a new shelf. The Bullseye connection sells shelves that they say are perfectly flat.

Steve

[charlie]

Of course Phil's suggestions are right on target.

If the shelf is the culpret (as I suspect it is) you could just get a new shelf. The Bullseye connection sells shelves that they say are perfectly flat.

Steve

i'm coming to the conclusion that flatness or wet wash isn't the whole story. i'm using a fiberboard shelf in making a series of 6 10"x20" panels, one at a time. they were cut from the same 2 complete sheets of glass. i prepped the board identically for each one.

2 of them blew half dollar sized bubbles, not in the same place. 4 of them were perfect. the glass was irid to irid, sandblasted a pattern in each one. the bubbles were not over a sandblasted area (ie it was in an irid to irid spot).

i used a very slow schedule from 1150-1300.

the distributer was out of b.e. irid, and so i used uro 90 instead. besides not having good intense colors that the be has, the glass wasn't completely flat.

i'm suspecting that there these small folds in the glass surface trapped air. i used very small chads in the corners to prevent this from occurring, but that didn't work out on all of them.

this was an expensive lesson, and i hope i can solve it without using up too much more glass.

[Phil Hoppes]

Hi Charlie,

Bummer Dude

I've heard from a few sources that the chad trick only works on smaller pieces. 10x20 might be a little large for that. I'm thinking you are right on the flatness of the glass. On the small sushi's we did in class I over etched on a few places and I got small bubbles between the glass where an irregular corner fit. Is the design the same on all pieces or is it a different design on each piece?

Phil

[charlie]

each piece has a different pattern. basically it's vines with hummingbirds, and they'll be mounted such that the pattern from one flows into the next panel.

it's an easier way to make a 2'x5' panel without having a big kiln, and having to start with 2x5' sheets of irid glass.

[Julieann]

I have a Paragon kiln using a 12x8 kiln shelf. I checked the level of the kiln, and it's perfectly flat. No variations at all (nice to know I can rule that out).

I'm making my own cabochons that I use in jewelry making, as well as some pendants. Usually I start with larger pieces, around 1 to 1 1/2 inch wide and 2 to 3 inches long that I layer colors on through several layers (letting the heat spread the glass into an even layer), before breaking up the piece to form the individual cabochons. Other cabs are created the right size to begin with, 1 inch round or smaller.

Like I said, I have done several firings where there were no bubbles. Everything came out great. It's only the last 2 that are showing these huge bubbles. I guess I was hoping that something I was doing was obviously wrong. And, in the very last firing, the bubbles were present in all sizes of glass pieces, from the large to the small. And the bubbles are occurring all over the board, not just in one or two places.

I'm wondering if the kiln wash didn't dry enough this time. I'm in Arizona, so usually it isn't a problem, but there has been a storm front that just came through that dumped some moisture on us. I think I'll try the suggestion to 'cure' it in the kiln before firing the next time.

Probably a stupid question: Can fiber paper be used more than once? Or do you have to throw it out after one use? (wouldn't that get expensive?)

So, what are the downsides of rigidized fiberboard?

[Phil Hoppes]

On the fiberpaper, yes you have to throw it out after you use it. That is why thinfire or Brads J110 is handy if you buy it in bulk the cost/fire is not too bad. Let's get back to your shelves. First a few questions:

1) When you checked the shelf for flatness did you look across at least two directions, that is to say did you put the ruler on one way and then go at right angles to that and look the other direction? Not trying to ask a stupid question but a shelf may be flat in one direction but wavy in the other.

2) How often do you kilnwash and do you scrape and clean the shelf before applying new wash?

If you checked both directions and you wash and clean between applications and only run a few fireings between wash then I'm out of ideas on your shelf. This would then classify itself as an evil kilnshelf.
I've had more than my share and so have most people on this board. If you like mullite shelves I'd get another shelf and try it. If it works fine, then I'd take your evil shelf and cut it up for kiln furniture. Daming bricks and the like. I've cut up about 4 shelve's to date because of this so you are not alone.

On the Fiberboard shelves, here are the +/-'s as I see it.

++
1) They are MUCH lighter. This is important for larger shelves, not so much for smaller shelves.
2) They breath much better than mullite shelves and in general will not bubble your glass. Charlie's troubles mentioned above may be the shelf but I'm thinking that it is probably related to the glass.

--
1) You need to kiln wash them every time. (At least in the beginning until you get a layer of old wash on them. Even then you should sand this clean in between wash's but you will always have some residue) Bottom line is you can't cheat like you can with a mullite shelf.
2) You may wish to use fiberpaper more.

Characteristics of both.
1) Cost - I'd say it is a wash on cost. Maybe on the smaller shelves, mullite might be a tad cheaper as I'm guessing the smaller sizes are probably more popular. Fiberboard may be a little cheaper to start but you have to rigidize them. After all is said and done they are probably close to each other in cost.
2) Smoothness - This is related to how they are made. I've seen very
smooth mullite shelves as well as fiberboard. I've also seen both that looked like they were used to pave a drag strip before I bought them. If you can see before buying that is the best way to go. Most times you can't do this so it is catch-as-catch can.

Phil

[Phil Hoppes]

Where in AZ are you? Charlie, me, Jackie and Cindy are all in the Phoenix area. My studio is up in Overgaard which is where I am most of the time?

[Jackie Beckman]

Phil said: On the fiberpaper, yes you have to throw it out after you use it. That is why thinfire or Brads J110 is handy if you buy it in bulk the cost/fire is not too bad.


I reuse my fiberpaper all the time, but maybe thats not what others do. If its the 1/8" I can use it at least 4 times, and the 1/16" at least twice, maybe three times. I sprinkle dry kiln wash over it each firing though, and lightly smooth it out with my hand.

Reusing it is not a big deal for small amounts, but when I need to roll it out the entire length of the kiln, it adds up quickly and I really see no reason to throw it away after one firing. Is there one I'm missing?

see you later Phil Hoppes-

Jackie

[Lani McGregor]

I reuse my fiberpaper all the time, but maybe thats not what others do. If its the 1/8" I can use it at least 4 times, and the 1/16" at least twice, maybe three times.

Yo, Jackie…. another Thrifty Woman … I’ve used ceramic fiber paper up to a dozen times. Unless you’ve just cooked the bejeezus out of the stuff and ripped it apart by over-firing your glass (tsk, tsk), you can use a long rigid cardboard tube (like the ones that the fiberpaper comes rolled on, or a PVC pipe) to roll the paper smooth after each use…. you can even roll the fiber paper up onto the tube and store it for later use.

This does NOT hold true for ThinFire (HEPA food)

Heloise

PS. How’s the boat party shaping up?

[Catharine Newell]

Jackie,

I agree! I have fibreboard shelves in my kilns and I line them both with 1/8" fibre paper, before firing atop thinfire. That 1/8" fibre paper stays in my kiln, in good condition, for a couple of months, at least. And those kilns are usually going 24-7. It's good protection for the shelf, ensuring a longer life. After each firing, I carefully vacuum up the thinfire, roll the fibrepaper with an old (heavy) thinfire tube, and then reline the surface with thinfire. It works great!

Catharine

[Catharine Newell]

Forgot to say, tho, that a great number of my firings are tack fuses... giving me more opportunities to use that same sheet of fibrepaper.


Catharine

[Jackie Beckman]

Heloise

PS. How’s the boat party shaping up?

Ahhh the big party on the boat . . . so exciting. Actually, we are about at 18, unless some people have changed their minds, and the good part is, we are a really, really fun group so far. I'm expecting more, but I figured I'd give it a little more time before bringing it up again - (I guess not everyone needs 6 months to shop for a dress - go figure. ) With all the exciting events this fall, people may need a little more time to make their plans. But no matter how many we are, it's going to be just too much fun. I keep thinking of that view of the skyline from the water . . .

[Phil Hoppes]

I was just thinking along the thinfire stuff. Yep, you can reuse the thicker stuff. I've got a box of the old thinfire which I'm trying to go through. I haven't tried the new stuff. It is suppose to not shrink which would be a good thing.

Phil

[Jackie Beckman]

I was just thinking along the thinfire stuff. Yep, you can reuse the thicker stuff. I've got a box of the old thinfire which I'm trying to go through. I haven't tried the new stuff. It is suppose to not shrink which would be a good thing.

Phil

Hey Phil, If you want, I'll share a roll of new thinfire with you? I'm going to order some - just did a piece fired face down on thinfire and its about 23" long and I can see the little seem from placing two sheets together. Grrrr!

What time are you coming here today?