The pic below shows irid pitting. The glass is BE (the irid is rainbow irid on clear). There are two irid layers (on top of another layer) -- never irid-to-irid.
The glass was fired twice -- both times irid down on thinfire. First firing was to about 1500F, the second to 1440F. Everything is flat - no slumping.
Holding the piece up to the light, there's clearly a lot of small bubbles behind the pitting.
I found reference to simillar problems in the archive -- but no answers -- so trying again here.
Any ideas on what is the root cause (and how to avoid it)?
Last edited by Paul Tarlow on Tue Jan 06, 2004 4:29 pm, edited 1 time in total.
This is another problem I don't think we ever solved. It's happened to many of us It appears as if the irid coating is actually attacking the glass like an acid. Mary Kay, any word from R&E on this?
Here is what I know about the phenomenon where occasionally the irid bubbles when in contact from the shelf release.
1. It happens only occasionally.
2. When it does happen, it seems to happen where the irid is silver color. The color of the irid comes from the thickness of the irid coating. The silver is the thinnest. so, when this does happen, it seems to be related to the thinnest coating.
3. The reaction can happen on ThinFire or on shelf primers or other papers.
4. However, the silver irid often fires successfully on ThinFire, shelf primers and other papers.
5. We don't know why this happens sometimes.
6. The best way I can suggest to avoid the reaction is to use gold irid or rainbow irid, which are thicker coatings, and seldom if ever show this reaction.
7. If you love silver irid, and you need predictable results, try to plan firings so that you can fire the silver face up, and avoid contact with the shelf release.
I've never had this problem until this week! Fired black rainbow patterned irid, irid side down on thin fire. In the second firing (to 1400) it pitted all across the entire back of the piece - really bad. Can send the piece to R&D if they are interested. It is a concern because all of my work uses black irid on the back. This glass was from the shipment I picked up a few weeks ago.
Here is what I know about the phenomenon where occasionally the irid bubbles when in contact from the shelf release.
1. It happens only occasionally.
2. When it does happen, it seems to happen where the irid is silver color. The color of the irid comes from the thickness of the irid coating. The silver is the thinnest. so, when this does happen, it seems to be related to the thinnest coating.
3. The reaction can happen on ThinFire or on shelf primers or other papers.
4. However, the silver irid often fires successfully on ThinFire, shelf primers and other papers.
5. We don't know why this happens sometimes.
6. The best way I can suggest to avoid the reaction is to use gold irid or rainbow irid, which are thicker coatings, and seldom if ever show this reaction.
7. If you love silver irid, and you need predictable results, try to plan firings so that you can fire the silver face up, and avoid contact with the shelf release.
That's what we know at this point.
Mary Kay
Thanks Mary Kay.
I can add this to the above information I posted:
--> After reading your message I went back and checked -- the piece uses both rainbow and silver (above I said only rainbow). The pitting is almost exclusively on the silver (consistent with your info above).
--> I read some more old posts -- one of the theories that was kicked around was that the problem was associated more with slumping than fusing -- specifically around where the glass is "stretched". This could jive with the theory that the thinner coating is more likely to pit -- since the coating is stretched in this scenario. Add to that that my pieces -- though not slumped -- were intentionally layed up thick and fired to 6mm which also would have stretched and thinned the irid.
--> After reading your message I went back and checked -- the piece uses both rainbow and silver (above I said only rainbow). The pitting is almost exclusively on the silver (consistent with your info above).
--> I read some more old posts -- one of the theories that was kicked around was that the problem was associated more with slumping than fusing -- specifically around where the glass is "stretched". This could jive with the theory that the thinner coating is more likely to pit -- since the coating is stretched in this scenario. Add to that that my pieces -- though not slumped -- were intentionally layed up thick and fired to 6mm which also would have stretched and thinned the irid.
- Paul
Paul:
This theory doesn't equate given I've been fusing with black rainbow irid on the backs of all of my pieces for the past 16 years and this is the very first time I've ever encountered a problem. Same firing schedule, same thickness. The only thing I did differently in this firing was to use thin fire. Before, I always used kiln wash. Guess I'll be going back to kiln wash and hope I don't encounter this problem again.
I've been having this problem for the past year and it happens on kilnwash too. I've seen the problem with black irid and cobalt blue transparent irid, mostly on silver irid or silver areas of rainbow irid.
My only solution is to only fire irid down on the shelf one time, any more than that and I get bubbles.
Take a look at the glass under the damaged irid (blast it off). the glass looks like sponge rubber.
Paul Tarlow wrote:The pic below shows irid pitting. The glass is BE (the irid is rainbow irid on clear). There are two irid layers (on top of another layer) -- never irid-to-irid.
The glass was fired twice -- both times irid down on thinfire. First firing was to about 1500F, the second to 1440F. Everything is flat - no slumping.
Holding the piece up to the light, there's clearly a lot of small bubbles behind the pitting.
I found reference to simillar problems in the archive -- but no answers -- so trying again here.
Any ideas on what is the root cause (and how to avoid it)?
I use my own material
I have this problem occasionaly
Been some mayB 20 years or so
Not found a reason or solution
But my guess is something 2 do with traped air or gass of some kind
Usually happens at side or corner rather than in centre n always on underside against the bat wash
I have been using same methods / materials a long time
Ron Coleman wrote:I've been having this problem for the past year and it happens on kilnwash too. I've seen the problem with black irid and cobalt blue transparent irid, mostly on silver irid or silver areas of rainbow irid.
My only solution is to only fire irid down on the shelf one time, any more than that and I get bubbles.
Take a look at the glass under the damaged irid (blast it off). the glass looks like sponge rubber.
Ron
Well, if that's the case Ron, it sounds like a new formulation in the irid coating on the glass perhaps. I've been using old inventory until this week...glass that I've had for past two years. Never encountered this problem before. The bubbles on this piece are everywhere. It looks like acid attacked the back. I run my pieces through at least 4 firings (irid down) and the design doesn't allow for any change in materials. This is very frustrating.
Ron Coleman wrote:I've been having this problem for the past year and it happens on kilnwash too. I've seen the problem with black irid and cobalt blue transparent irid, mostly on silver irid or silver areas of rainbow irid.
My only solution is to only fire irid down on the shelf one time, any more than that and I get bubbles.
Take a look at the glass under the damaged irid (blast it off). the glass looks like sponge rubber.
Ron
Well, if that's the case Ron, it sounds like a new formulation in the irid coating on the glass perhaps. I've been using old inventory until this week...glass that I've had for past two years. Never encountered this problem before. The bubbles on this piece are everywhere. It looks like acid attacked the back. I run my pieces through at least 4 firings (irid down) and the design doesn't allow for any change in materials. This is very frustrating.
Avery
I'll have to look at the date on my sheets. I know it is at least a year old.
I've seen this happen to System 96 Uroboros black irid (not silver irid) fired face down as well as Spectrum 96 black with mica on the surface (again face down) on kilnwashed shelves. I posted about it months ago, but only Ron and I had experienced it at that time.
Since it seems to be independent of manufacturer, it leads me to believe that there is something else going on here...
Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
I am not aware of an irid formula change but am certainly happy to check on that if you can give me the sheet glass production date and style number for the rainbow irid that is acting weird.
Meanwhile, I think your idea of switching to kilnwash for firing irid face down is a good idea, if the only variables which have changed are switching to ThinFire and using a newer batch glass.
Afer I find out whether or not there was a formula change I'll contact you offline and we can discuss whether it would be helpful for us to do further testing with that glass, shelf release and cycle you are using. (If we do testing I'll need more info re your firing cycles for each of the four firings.)
It appears to me to be almost like the irid coating is eating the glass. In the most egregious example I have seen, the glass could be crumbled away with finger pressure in the affected areas. Is the irid coating a mild acid? Is it being applied unevenly, and therefore attacking the glass more, in some areas? Brock
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.
david williams wrote: 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.
Calling it a foam is appropriate since the surface under the irid has millions of tiny bubbles. Just a thought, but I've never seen it when the irid is fired face up, so maybe prefiring the irid face up to 1200° or so will bake out the irid/stannous chloride coating and reduce the problem???
Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
I have a little more information to add to the points I mentioned above---actually a correction: while testing a year or so ago, we did see a trend for the irid reaction based on which shelf separator was used.
The irid foamy bubble reaction does seem to happen more often when the irid is in contact with ThinFire (but not always). Thinfire works best fired against uncoated surfaces.
The reaction should not happen at all with Bullseye irid on Bullseye Shelf Primer, which we reformulated last year to make it non-reactive to irid fired face down on it. (We tested only Bullseye irids during the reformulation.)
So, Paul and Avery, it looks like a successful solution may be to stop using ThinFire to fire irids face down, and to try Bullseye Shelf Primer instead.
I have a little more information to add to the points I mentioned above---actually a correction: while testing a year or so ago, we did see a trend for the irid reaction based on which shelf separator was used.
The irid foamy bubble reaction does seem to happen more often when the irid is in contact with ThinFire (but not always). Thinfire works best fired against uncoated surfaces.
The reaction should not happen at all with Bullseye irid on Bullseye Shelf Primer, which we reformulated last year to make it non-reactive to irid fired face down on it. (We tested only Bullseye irids during the reformulation.)
So, Paul and Avery, it looks like a successful solution may be to stop using ThinFire to fire irids face down, and to try Bullseye Shelf Primer instead.
Mary Kay
What about the thicker fiber papers? Or prefiring the paper?
I need the escape route for air with the design I'm working on -- and firing face up yields a very different end result.
My apologies.. I was mistaken about the glass I used being from a recent production run. It was manufactured in 2001, so it seems we can eliminate any recent changes in formulation. The only variable is the thin fire, so as Mary Kay has advised, I will be using kiln wash again.
Avery Anderson wrote:My apologies.. I was mistaken about the glass I used being from a recent production run. It was manufactured in 2001, so it seems we can eliminate any recent changes in formulation. The only variable is the thin fire, so as Mary Kay has advised, I will be using kiln wash again.
Avery
Problem does seam 2 B 2 do with the metalic stuff rather than manufacturer
We been using exactly the same batch of materials unchanged for about 8 years or so, same bat wash batch etc
We specificaly buy in bulk 2 get arround Constansistancy problems
And I still get this problem occasionaly
Just enough 2 let me know who is in charge
But been having this stuff happen exactly as David discribed some 20 or so years
I am big on Consistancy Evenivity n all that stuff
But just seams 2 happen by chance
I 2 think its some traping / none movement of air weirdness
