Irid pitting - revisited

David Williams · Post by **David Williams** » Mon Jan 05, 2004 7:36 pm

Thanks Brock. So Mary Kay can you all hazard just a reckless guess about what might be causing this? If you have reformulated the kiln wash so it won't react, what did you change about it? (I do use Bullseye kiln wash exclusively) If it is a reaction with the release, and it happens with both fiber and wash, what do kiln wash and fiber paper have in common? I have some marketable design ideas that have been on the shelf (as it were) because I couldn't overcome this problem. I wonder what Avery has been doing right all this time that she just now encountered the problem. I would sure like to beat this problem.

Avery Anderson · Post by **Avery Anderson** » Mon Jan 05, 2004 9:00 pm

david williams wrote: I wonder what Avery has been doing right all this time that she just now encountered the problem. I would sure like to beat this problem.

Hi David:

With the only variable being the thin fire, that's my guess as to the culprit as well as what Bullseye has determined. Although, I find Tony's recommendation of firing irid side up in the first firing an interesting idea with merit and I will try it if I encounter more problems. I have 5 more sheets of rainbow irid from the same run, so I'm going back to my old way of running the firings. I usually fire the full fuse on J-110 (1450). The second firing on BE kiln wash (1400), the third firing on BE kiln wash (1400), and then slump in a SS mold coated with Boron Nitride. This is what I've done for years with no problem. Brock and I encountered this problem in two of our classes using irid side down, but I can't remember if we used thin fire during those sessions.

I'll let you know how the next firings go, using the same run glass and old firing procedures.

Avery

PDXBarbara · Post by **PDXBarbara** » Mon Jan 05, 2004 9:30 pm

david williams wrote:Right it does happen with Uroboros and it happens on the spectrum I irridize with stannous chloride. So its not a lot problem or specific to any one manufacturer. Also as MK said it does happen regardless of the release you use. My theory is that it doesn't have anything to do with a reaction with the release. That the tin outgasses some tiny amount and when the glass is inverted and fired against the shelf the gas is trapped and rises and breaks some moleculor bond or acts like a flux (who knows?) and turns the glass to foam. It also doesn't seem to be a reaction with any glass colorant since it happens with different colors. I've never seen it happen on a slump. I don't believe irrid stretches. Breaks yes.

Hi David & everyone... It happened to me during a stainless steel slump. I started a thread about the problem a few months ago. Perhaps it's the same problem being discussed in now, or not. However, you can check out that thread at:
http://www.warmglass.com/phpBB/viewtopi ... highlight=

You can see pix of my glass with the problem at:
http://www.pbase.com/pdxbarbara/crystal ... ystery_pix

I'd made similar pieces a number of times... same glass & all... but the screwy one was the first time slumping it on SS after fusing on thinfire. Other than this, I've never had a problem w/ Irid side down.

Funny thing... Just a couple days ago, I blasted the screwed-up irid from this piece. Underneath... still kinda pitted. I'm going to take it back up to fusing temp. & see if it heals.

PDXFebruary

Ron Coleman · Post by **Ron Coleman** » Mon Jan 05, 2004 10:12 pm

Avery Anderson wrote:
david williams wrote: I wonder what Avery has been doing right all this time that she just now encountered the problem. I would sure like to beat this problem.
Hi David:

With the only variable being the thin fire, that's my guess as to the culprit as well as what Bullseye has determined. Although, I find Tony's recommendation of firing irid side up in the first firing an interesting idea with merit and I will try it if I encounter more problems. I have 5 more sheets of rainbow irid from the same run, so I'm going back to my old way of running the firings. I usually fire the full fuse on J-110 (1450). The second firing on BE kiln wash (1400), the third firing on BE kiln wash (1400), and then slump in a SS mold coated with Boron Nitride. This is what I've done for years with no problem. Brock and I encountered this problem in two of our classes using irid side down, but I can't remember if we used thin fire during those sessions.

I'll let you know how the next firings go, using the same run glass and old firing procedures.

Avery

I haven't fused on thinfire for several years and I've been having this happen on BE kilnwash usually on the third firing against the shelf but sometimes on the second firing. I've even had it happen to a piece that was fired with the irid up the first time and then down the second firing.

I'm using the latest BE kilnwash too.

Ron

Barbara Muth · Post by **Barbara Muth** » Mon Jan 05, 2004 10:15 pm

when I tried re-fusing the pitted irid face up, was still holey and crumbly. Smush the glass and a gazillion holes appear. All that stands between you and the sponge holes is the irid coat.

And I have gotten pits also on the green to purple end of the rainbow of an iridized purple. At the time I figured it was just my luck with some curious glass I had bought. Hold a transparent pitted irid to the light and you will see a ton of bubbles. Gassing makes sense to me. I was thinking along the same lines as Tony, but he beat me to the punch.

back from the flu girl... Barbara

PDXBarbara · Post by **PDXBarbara** » Mon Jan 05, 2004 10:24 pm

Barbara Muth wrote:
back from the flu girl... Barbara

Welcome back from the flu, girl...
xxoo
PDXBB

Tony Smith · Post by **Tony Smith** » Mon Jan 05, 2004 10:28 pm

Ron Coleman wrote:I haven't fused on thinfire for several years and I've been having this happen on BE kilnwash usually on the third firing against the shelf but sometimes on the second firing. I've even had it happen to a piece that was fired with the irid up the first time and then down the second firing.

I'm using the latest BE kilnwash too.

Ron

Well, that rules out prefiring the irid as a potential cure.

Tony

David Williams · Post by **David Williams** » Mon Jan 05, 2004 11:12 pm

I can't really see how the glass would get hot enough to react that way on a slump firing. What may have happened is that you didn't notice the pitting after the fuse. Thats possible. Sometimes the irrid is still fairly flat and it masks the problem. The only reason I quibble about that is I think that if we all put our experiences together, and try and figure out exactly what is happening--its the only hope of solving it. If it really were possible for this to happen at such a low temp as a slump fire, that would be a very important clue in my mind. Not many reactions can happen at those temps.
I haven't heard anything I can put my finger on as any new information or suggestions, maybe I'm reading the posts wrong. What I'm really afraid of is that there is no solution. That this just happens as a reaction between these materials. But what keeps gnawing at the logic of this is, why does it happen inconsistently? Something we are doing must trigger it. Or, its in the coating process. But if you look at for example BE or Uro's process, they shoot it before the glass has ever cooled down, after it is rolled. My process is very different, I heat up cold glass and shoot it. Yet the same thing can happen to both glasses.

Paul Tarlow · Post by **Paul Tarlow** » Mon Jan 05, 2004 11:23 pm

PDXBarbara (Bader) wrote: I'm going to take it back up to fusing temp. & see if it heals.PDXFebruary

Last night I put my piece on a light table and proceeded to scrape out the pits with a fine pointed tool. I then filled the pits with powder and refired to 1400 with a 2 minute soak. For the most part it "healed" -- the "spots" are quite noticiable -- but at least it isn't a hazard anymore.

- Paul

Phil Hoppes · Post by **Phil Hoppes** » Tue Jan 06, 2004 12:39 am

Interesting thread. I had this happen to me about a year ago on a piece of silver irid clear. It was a fluke and at the time was about to scrap the piece until I discovered some interesting things that I could do with it. I haven't had much time to work on it in the mean time but while all of you are trying to get rid of this effect, I'd like to enhance it and be able to reproduce it on demand so to speak. If an answer is found, I'd like to know.

Phil

Kevin Midgley · Post by **Kevin Midgley** » Tue Jan 06, 2004 12:39 am

Firing shedules at this time of year are longer as the supplied voltages are commonly lower owing to the massive power consumption of colder weather and holiday lighting demands. This "invisible" extra firing time could be allowing more bubbles to form. Try firing after midnight when general power demand and consumption is lower. Kevin in Tofino

Phil Hoppes · Post by **Phil Hoppes** » Tue Jan 06, 2004 12:46 am

Hmm, not sure I follow that logic Kevin, at least for all of us with computer controllers. The inputs to those systems are ramp rates and hold times. These are, for the most part, independent of voltage. The computer ramps the kiln at the rate required. The program does not have a memory of the characteristics of your kiln, it simply measures the change in temp vs time and either increases or decreases the amount of time the elements are on. If the voltage is lower at any one time (assuming it does not drop completely) the computer will compensate for this and simply leave the elements on for a longer time to accomplish the program. Lower voltage should not change the results of the fusing schedule. The only possible thing affected by the cooler weather is that the kiln will ramp faster cooling down, in which case one should probably pay attention to the end of the program least the kiln and the glass cool too quickly after the end of the program is reached.

Phil

Kevin Midgley · Post by **Kevin Midgley** » Tue Jan 06, 2004 12:58 am

The fact that the controller "may" have to compensate during the firing schedule is what I am talking about. People using the irrid glass are looking for possible reasons for their problems. I just wish to point out that some things everyone thinks are the same are not always exactly the same. If a kiln cannot go "as fast as normally possible" because its supplied voltage is lower then the controller will have to compensate with a longer time to reach its goal. That longer time might be the problem in some cases. Kevin in Tofino

David Williams · Post by **David Williams** » Tue Jan 06, 2004 1:03 am

It is an interesting sort of lava effect. I know a potter here in Hawaii who uses a pin and pokes a million tiny holes in clay vessels to create that effect. On the other hand, I don't think the glass in this state is very stable. Which brings up a more serious question about this problem--does it call into question the food safety of uncapped irrid. You can imagine that there could be more pitting happening in irrid fired objects than we ever detect, and the irrid could flake off later. I don't know if tin in this state is inert. I remember there was a guy on Craftweb who speculated that tin was as toxic as mercury. Not a statement that made sense to me, but there it is.

Tony Smith · Post by **Tony Smith** » Tue Jan 06, 2004 7:15 am

Kevin Midgley wrote:The fact that the controller "may" have to compensate during the firing schedule is what I am talking about. People using the irrid glass are looking for possible reasons for their problems. I just wish to point out that some things everyone thinks are the same are not always exactly the same. If a kiln cannot go "as fast as normally possible" because its supplied voltage is lower then the controller will have to compensate with a longer time to reach its goal. That longer time might be the problem in some cases. Kevin in Tofino

I agree with Phil here. The only time lower voltage will impact the actual firing time will be when the kiln elements are full on, and that's rarely the case with the firing schedules that we use. Besides, I've seen this happen in both my computer controlled kiln where I take hours to get to full fuse and my little "balls to the wall" baby kiln where I'm at full fuse in thirty minutes. Time doesn't appear to be a factor in the equation.

On top of that, for some unknown reason, our electric company installed a brand new transformer on the electric pole outside my house. My voltage is now rock solid stable year round... (I wonder if the neighbors were complaining about their lights dimming when my compressor kicked on while I was running two kilns during the summer when the central air was running?)

Tony

Phil Hoppes · Post by **Phil Hoppes** » Tue Jan 06, 2004 8:29 am

Kevin,

AFAP is the ONLY ramp that low voltage may affect someone. I don't know your schedules but I never ramp up AFAP I only cool down at that rate so the elements are not on, thus low voltage is not a factor. When I set my controller to ramp at 100 DPH it will ramp at 100 DPH regardless of the line voltage assuming it is within the tolerance window for the supplied voltage and it is not so low as to trip out the line control sensor on my controller. If the controller is set to hold at 960 for an hour, it will hold at 960 for an hour regardless of the line voltage. Line voltage is simply not a factor on firing schedules. External temperature is wrt cooling the kiln when the controller has finished it's schedule. If the area where your kiln is placed is cool, ie a garage, and your line voltage is low for what ever reason, what you will see is a larger cost per firing as your elements will be on for a longer period of time for a given schedule. Your total firing schedule time should not change, at least within a reasonable margin, ie a few minutes over a 10 to 12 hour firing schedule. I see some minor changes with total firing time in my kiln but that is usually due to the load in the kiln, which is affecting the AFAP ramp time I'm sure. When you do uncontrolled cooling, that rate is dependant on the kiln itself, the load in the kiln and external factors like temperature. That is the reason you may see different total firing times for the same schedule. If you are seeing large variations on your firing schedules based only on seasonal variations, I would look into getting another controller as something is seriously wrong with your controller.

Phil

Tony Serviente · Post by **Tony Serviente** » Tue Jan 06, 2004 11:38 am

For what it's worth, I do quite a bit of face down firing of Spectrum Irid (Non System 96), and have never seen this problem, or even a hint of it.

Phil Hoppes · Post by **Phil Hoppes** » Tue Jan 06, 2004 11:45 am

Back to the problem at hand....

I was curious when I first saw it if it was related to moisture, possibly getting trapped between the irid layer and the glass. Makes sense possibly, especially if silver is the one that appears to exhibit this problem most and it is the thinest of the irid coatings. In my case, the glass surface looked like a sponge with lots of pockets. I sandblasted the irid off to get a better look at the surface. Clearly, something was producing a gas at the time while the glass was molten and held the pockets in place until they were frozen in place after the glass was cooled. I was planning on doing an experiment soaking some of the glass on purpose for different lengths of time and then doing a fusing firing to see if I could force the bubbling to occur. With the discussion on kiln wash and fiber paper it sounds to me like we need to do an N-Factorial experiment. What do you think Tony?

Phil

David Williams · Post by **David Williams** » Tue Jan 06, 2004 12:39 pm

I've heard that theory before; that the silver is thinner so maybe moisture is coming up through it. I don't think thats it, for two reasons. First, you would have to assume that the tin coating is not only gas permeable--an assumption I find hard to make--but also that there is less of a pressure gradient up through the metal than between the shelf and the glass (out the side). Its just not plausible theoretically. Also, its not borne out by experimentation. I've gotten this problem and I use bone dry, baked kiln shelves.

Phil Hoppes · Post by **Phil Hoppes** » Tue Jan 06, 2004 1:05 pm

Point taken but something I belive is producing some kind of gas that is causing the openings, either that or the glass is being disolved some how and I don't believe that is going on.

Phil