Yet another Bubble issue- but a specific one

[Davidknox]

9/28/03

Fellow- Bubble warriors,

I have gone through the archives and the new listings- did not see this one. Has anyone ever had specific problems with large, aggressive bubbles using large pieces of Bulleyes 1412-30- that sparkly green semi-transparent glass? It is happening in the glass- like volcanic eruptions. Here is my problem and I know it is related to that glass but am desparete for a solution. I have now made my 3rd rendition and perhaps my 7-8 th total firing of a rather large panel-30X 20 with a total thickness of just over a half inch- and I am still getting bubbles despite changing designs and firing formulas. The stack up is as follows:

1/8th texture irid clear- irid down on fiber blanket.- 28" X 18"
1412-30 - same size as first layer
dichroic design features glued together on different cathedrals- (large, many, detailed matched cutting- tearfully expensive, hand cramping work)
1401-03 coarse frit filling in the spaces of the design and then on top of the whole piece.- about 10 lbs of frit.

I first didn't use the frit- I used cut pieces of ripple glass kind of stacked in-between the design elements. This is how I usually do it and have NEVER had this problem. I use medium and coarse frit to cast with everyday and NEVER this get this problem.

Anyway, the clear Irid base glass is fine- intact, no bubbles. It is not happening inbetween the shelf and the glass. it is not happeneing in-between the design elements and frit. The green is volcanic- it will come up right through the glass I have the Dichroic on and actually break the dichroic coating, finally emerging through the clear. It appears to happen right around 1470-1500.

My schedules have been varied as i have sought to kill the beasts but basically last nights was this:

300/1100-h30
250/1250-h 45
700/1500-h5

Anneal appropriately as per thickness and size.

In desparation, a couple of firings ago, I saw the crater field and opened up the kiln at 1525, took an acetylene torch ( adult supervison required) and blasted the surface in hopes of raising the little buggers out and exploding. No luck. I said screw it- I ramped the kiln up to 1600 and held it for 30 minutes. The bubbles boiled out but the design elements basically floated off into space and the piece was filled with green "holes" in the midst of the other colors. Turned out beautifully- for my garden- but not what I drew and was commisioned for. I also tried refire with piece flipped over to get the bubbles to float back to about the middle- with a plan to flip back over and fire polish. Green rivers running through the design. another garden sculpture.

Latest rendition is in kiln, still warm, and is the best so far. I got about 6 large bubbles (quarter size) but they remained within the 'green" area and did not intrude up the other colors. They came up just at about 1500 and so I popped them and finished the annealling program and now have 1/2 deep craters to fill.

My 1st question is this: Has anyone seen this problem- a glass that seems to simply bubble when it is large? I have used that glass a ton of times and found it to flow really well. I have never used a piece this big. Since I have done this 3 times, it is not all from the same batch from Bullseye.

2nd ?- most important; To fill the holes and correct the problem, if I fill them with frit or chunks of glass, I will have to take it up rather high to melt and flow it. I am afraid- sure in fact- that more bubbles will come up if I do that. What are peoples's thoughts on perhaps soaking a long time at say 1425-1450max to just use time to melt the filler glass in the craters- using perhaps a 1401-30 broken up into chunks or some dichro elements to cheerfully hide the errors. I am using mainly a top fired kiln and dam the edges with fiber blanket.

2a. Should I use a tiny drill to open the holes I see that are close to the surface to at least release the air for the next firing or is that simply going to collapse those?

3rd- Do you think that the soaking at 1100 and 1250 is actually hurting the process rather than helping since the bubbles are not occuring between the layers but actually in the glass itself. I was thinking that perhaps a faster ramp might not let the air bubbles form inthe softened glass something- like a faster transisition.

I did think about using 1412-03 coarse frit instead of the sheet glass but when i ran an experiemnt, it simply wasn't very pretty.

thanks for your help. If there is something in the archive that addresses this specific bubble problem, I would appreciate it. Otherwise, I really could use any thoughtful thoughts- or unthoughtful impulses.

best, David Knox

[Lisa Allen]

I know that you think that the bubbles are not in between layers of glass, but it might be worth assuming that the space between the textured irid and the adventurine green is sealing off too fast at your current ramp rate of 250dph between 1100 and 1250 and trapping air that volcanos when it gets to full fuse.

I have successfully avoided those kinds of bubbles with a much slower ramp of 50dph between 1100 and 1250. It allows so much more air to escape before the edges seal up. Might be worth a try.

Lisa

[Geri Comstock]

In many kilns, you don't have to go to 1500 for a full fuse. That may be part of the problem.

Try your full fuse at a lower temp, but hold it longer.

Geri

[Davidknox]

Lisa,
I thought about it after I wrote the post and I think you might be right. I am probably trapping inbetween the base and the green. It's just funny that I haven't had this before. Might be the weight on the upper layers causing a slumping seal in pockets and the green is pretty bumpy and brittle as you know.

Thanks Geri- I needed to go to 1500 because of the frit. It really could use another 25-50 degrees for pure clarity but I can't deal with the bubbles there. Perhaps a longer soak at lower will work but I haven't found much luck with clarity at lower temps.

Any more suggestions on the hole filling and the tiny drilled holes?

Thanks again to Lisa and Geri.
David

[Geri Comstock]

It sounds like you're trapping air. Do a "squeeze" at about 1180. I recently wrote a post about how to do this.

Filling holes is problematic. I've used frit, chunks of glass I crushed from sheets. Often the hole repairs show, or blow out again when you take it to full fuse.

Good luck with this!

Geri

[Davidknox]

Thanks Geri-
As I said in my experience the frits usually need to go higher temps to get the clarity I like. Have you had luck soaking large or coarse frits at lower temps and getting them to flow well and have a high clarity? I simply haven't done that one and would like any advice on that available.

I am having some second thoughts about whether it is trapped air between the irid glass and the green because it appears to be right in the middle of the green glass. I can see through the clear irid and there is no appearance of bubbles forming like they do between the kiln shelf and the base glass. It may just appear that way because the bubble collapses- or some of it does- at some point and some falls back on the clear glass. Sort of like folding a bubble-gum bubble over and blowing it again.

If it is the air trapped between the base and the aventurine green, could I drilled a whole series of small holes in the irid base glass- on 1" centers or something and do a another slower soak ala Lisa or Geri's (haven't looked for that one but I imagine it's a slow soak method). The piece is well formed and hefty so I'm not risking much in doing so.

Any and all opinions are welcomed.

Thanks Again, David

[Lisa Allen]

I have actually gotten rid of small bubbles that way. The top of the piece had a rashy look to it, so I flipped it over and drilled into each of about 10 bubbles. This piece had a clear base and an opal top, so it was easy to locate the bubbles from underneath. I refired on thinfire so the air could escape and the bubbles collapsed down and were not noticable at all from the top of the piece.

I have never done this with a volcano though. I imagine that the glass has thinned out so much that it will be noticable in the fix even if all the air does escape. Plus the glass is all transparent and your holes will leave scars that will be visible from the top. Might look interesting though, depending on your design....... Sounds like the piece is pretty much toast anyway, so I would give it a try.

Lisa

[Barbara Muth]

David, if you are not accustomed to doing pieces this big, you may be trapping the air on the same speed ramp up because of the size of your piece. It is closer to the elements so you are probably more likely to seal the edges before squeezing the air out , and you have the possibility of trapping a larger volume of air inside the piece. I would try ramping up a bit slower and soaking a while at a low temp like Geri suggests. I sometimes do two soaks, one at 1050 and another at 1150.

Regarding the piece, it has been my experience that I can't save a bubble piece. The concentration of color is deeper on the outside ring and much lighhter in the middle. Even if you fill in the holes and don't disturb the irid pattern, you will probably have rings. Of course, if you can work with that great! If you think you may have more bubbles that want to come up, you could flip the piece over and let them all "boil" out the back, then fix it.

Barbara

[Davidknox]

Lisa, Geri and Barbara,

Thank you all for the advice and suggestions. I took a closer look and sure enough, you folks were right- I had sealed off about 4 inches around the rim of the part and had created a central air gap that was the source of the bubbles. I had been doing two different soaks- one at 1100 and one at 1250 and had dammed the sides of the entire part with fiber blanket. I obviously need to go slower or find different soaks as you suggested and perhaps use some shims on the edges.

I actually fire large slabs pretty much daily but have not seen this problem because the construction of them is entirely different- but didn't think about that when I built this one. I think that I had so much invested and had tried so many different things, I kinda got a little lost on what was happening.

So again, thanks all for your help getting back to home! By the way, the 1412-30 fired out to 1600 and held for awhile becomes incredibly different and i believe stunning.

Best Regards, David Knox

[charlie]

By the way, the 1412-30 fired out to 1600 and held for awhile becomes incredibly different and i believe stunning.

Best Regards, David Knox

pictures? i used some of this under a clearcap and it adds a shimmering to it, and this glass seems to have internal lines where it looks like it's been folded that show up under a clearcap with really interesting waves.

[Davidknox]

Charlie,

I have some photos of the various stages of the projects and different iterations and the "cosmic, swamp green".

i don't know how to attach them here. Can you give me a regular e-mail address or tell me how to do it?

Thanks, David

[Tom White]

David, do a Google search for free photo hosting. Pick one (I've seen Webshots, Picturetrail and Yahoo most often here). Sign up. Create a gallery open to everyone. Upload your pictures. Copy the link to your gallery and paste it in your post to WGBB.

Best wishes,
Tom in Texas

[charlie]

or if they're already on a server somewhere, use the Img button, type in the url to them (or cut/paste from somewhere), then use the Img button again to close it. the jpg will then be shown in your post.

you can also use the URL button instead of Img, and the path will be inserted into your post as a clickable link.

[Davidknox]

These are just my internal photos so barbara Muth was kind enough to say she would post them on list or whatever. I emailed some to her last night. I'm just jammin right now and don'tr ahev time to mess around with the phot stuff. I have cut up the main piece and removed the salvagable parts and am once again recreating. I really like how it's coming right now so once again, I think it was worth the effort and the mistakes are not at all.

Thanks, David