Pyrometers..plates...bubbles agrhhhh!

[Carla Fox]

I am convinced I need to know the real temperature in my kiln (an evenheat coffin kiln) so I can figure out what is going wrong with my schedules.

Several months ago one of you told me where to get a pyrometer and I have lost that info when I switched over to a new zippy computer.

So could I have it again?

Specifically what my problem is: I am fusing 2 full circles of glass (BE) in 8.5" diameters. I have big ugly misshappen bubbles inbetween the layers.

Maybe one can't slow a kiln down enough to get these out as it's a long way from the center of the circles to the edge, or maybe it's a heating problem. I'm determined to figure this out and get some control over this.

My schedule is (based on some input from ya'll a few weeks ago):

200º/hr to 1180º hld 40min
50º/hr to 1250º hld 8min
400º/hr to 1425º hld 8min
9999 to 960º hld 30 min
then let it cool off.

I have checked to see if my glass is double rolled, it is. I put smooth sides together. So now I am thinking I need to know what the temp REALLY is in my kiln.

Any input on any of this is greatly appreciated.

Carla, so tired of asking bubble questions, please be kind in answering yet ONE MORE stinkin bubble question

[Brock]

Your schedule is fine, conservative even. I think you are right, you aren't getting an accurate reading, because you should have no trouble with bubbles with that schedule. Can't help you with the pyrometer, but have you tried the beads/chads/Brads/blips technique. It works very well. BrockSpecifically what my problem is: I am fusing 2 full circles of glass (BE) in 8.5" diameters. I have big ugly misshappen bubbles inbetween the layers.

Maybe one can't slow a kiln down enough to get these out as it's a long way from the center of the circles to the edge, or maybe it's a heating problem. I'm determined to figure this out and get some control over this.

My schedule is (based on some input from ya'll a few weeks ago):

200º/hr to 1180º hld 40min
50º/hr to 1250º hld 8min
400º/hr to 1425º hld 8min
9999 to 960º hld 30 min
then let it cool off.

I have checked to see if my glass is double rolled, it is. I put smooth sides together. So now I am thinking I need to know what the temp REALLY is in my kiln.

Any input on any of this is greatly appreciated.

Carla, so tired of asking bubble questions, please be kind in answering yet ONE MORE stinkin bubble question
[/quote]

[Carla Fox]

Ack. The plate is not 8.5" across, but 10.5" across.

Thanks Brock. I will go check the archives for Brad's beads.

Carla

[charlie]

i think your kiln temp is off, which btw could also lead you to not annealing properly.

i use almost the exact same schedule as you. no beads. i just pulled a 21" diameter circle 2 layer plate out of the kiln and it had a few tiny (1/16" maybe) bubbles.

[Brock]

The size is immaterial when you use beads. Just cut up some compatable glass into little squares, 1/4", 3/16", whatever. Fire them hot, up to 1500F, and they will ball up and become perfectly round domed beads. These can be used as spacers, and design elements in your work. I actually cantilever them over the edge of the bottom disc, then grind them back after firing. Br careful you don't have them too far in from the edge of your disc, or you can trap air around the beads when the top blank slumps down onto them.

Try:

300F to 1100F - Hold 30
100F to 1200F - hold 30
100F to top temp
300F to anneal - Hold 60
100F to 760 - Hold 30
Cool

Works for me on pieces as big as 19" round. Brock
Down to room temp

[Carla Fox]

So Charlie was it you who gave me the pyrometer info, or was it Tony?

As to annealing...interesting you should mention this. We are making plates out of two pieces of lite colored glass and then sandblasting designs on them. We had a bunch at a show and every once in a while I when I would say they are dishwasher safe, someone would say "OH, no, they're too fragile." And I would respond by banging them solidly on the edge of a wooden table. Did this all show long. I kept telling myself to stop this as I would break one. But the ham in me wouldn't let me stop. So I know they are annealed okay.

I'm going to try Brock's idea as well as check the pyrometer. Maybe I'm off at the starting end.

Thanks you guys. I'm going make little beebees and see what happens. But I'm also testing this kiln. This is silly to not be able to get a hold on those damn bubbles.

Carla

[Tony Smith]

Carla,

Have you tried your fusing schedule while firing on ceramic fiber or thinfire? That would prove/disprove the pyrometer theory and perhaps point to the kilnshelf.

Tony

[Brock]

. . . I have big ugly misshappen bubbles in between the layers.

Thin fire will have no effect on these bubbles Tony. Brock

[Carla Fox]

More info then you need.

I do have a computer pyrometer ramp up-down thingy on my kiln.

The pyrometer I am talking about is one to double check the accuracy of the in-kiln pyrometer.

I did a search of the archives and found a link to CentredeVerre and will call and talk to them tomorrow.

This has been an ongoing problem. I started with "champagne" bubbles little pin pricks and now have big lumpy ones. Same kiln, same schedules. So I don't think it's the shelf.

I think the temp is shifting in my kiln.

I will try Brocks chads/beebees but also I want to see what's the real temp in the kiln.

I diddle with my schedule and then the big buger bubbles go away. Then wham they are back again.

Thanks for all your helpful thoughts. It gives me something to process on while I try to solve this once and for all! Or at least understand it.

Carla

[Carla Fox]

More info then you need.

I do have a computer pyrometer ramp up-down thingy on my kiln.

The pyrometer I am talking about is one to double check the accuracy of the in-kiln pyrometer.

I did a search of the archives and found a link to CentredeVerre and will call and talk to them tomorrow.

This has been an ongoing problem. I started with "champagne" bubbles little pin pricks and now have big lumpy ones. Same kiln, same schedules. So I don't think it's the shelf.

I think the temp is shifting in my kiln.

I will try Brocks chads/beebees but also I want to see what's the real temp in the kiln.

I diddle with my schedule and then the big buger bubbles go away. Then wham they are back again.

Thanks for all your helpful thoughts. It gives me something to process on while I try to solve this once and for all! Or at least understand it.

Carla

[Carla Fox]

More info then you need.

I do have a computer pyrometer ramp up-down thingy on my kiln.

The pyrometer I am talking about is one to double check the accuracy of the in-kiln pyrometer.

I did a search of the archives and found a link to CentredeVerre and will call and talk to them tomorrow.

This has been an ongoing problem. I started with "champagne" bubbles little pin pricks and now have big lumpy ones. Same kiln, same schedules. So I don't think it's the shelf.

I think the temp is shifting in my kiln.

I will try Brocks chads/beebees but also I want to see what's the real temp in the kiln.

I diddle with my schedule and then the big buger bubbles go away. Then wham they are back again.

Thanks for all your helpful thoughts. It gives me something to process on while I try to solve this once and for all! Or at least understand it.

Carla

[gone]

Hi Carla,

How about doing the "Know your Kiln" test that Bullseye suggests in one of their tip sheets? It will tell you at which temps your glass is softening, show you your hot and cold areas, and also your annealing range.

Els

[Tony Smith]

. . . I have big ugly misshappen bubbles in between the layers.

Thin fire will have no effect on these bubbles Tony. Brock

Ahhhhh yes.... missing the obvious again!!!

oblivious boy

[Nancy Juhasz]

Hi Carla, I also have the Evenheat coffin kiln. It is new and have only done a couple of test fires in it because I am getting bubbles and also know the temps are to high for what I am doing. I am slumping bottles and am now down to 1400 no hold to get a nice flat bottle and ramping at 400-1000-10
100-1300-10
400-1400-0 then down with my anneal. I am getting hugh bubbles on the bottle to shelf. Have checked the shelf with a straight edge it is even and the kiln is level. My solution was I was going too use fiber paper and be done with it. Maybe I should get a pryometer and check the temp. Perhaps this kiln runs more even so we don't have to use as much heat. I was sacrificing beer bottles not wine bottles for the test. I'm back using my little kiln as my workhorse until I get this figured out. Any suggestions welcome.

[Stephie]

Here is another place to get thermo & pyrometers.
http://www.omega.com/

[Carla Fox]

Nancy:

My bubbles are between my layers of glass. I'm on a pyrometer search and will report back on all my findings and solutions.

Carla

[Mary Kay Nitchie]

Nancy:

My bubbles are between my layers of glass. I'm on a pyrometer search and will report back on all my findings and solutions.

Carla

Hi Carla--

I've been doing some similar firings and this schedule has been working well in my really old, beat Paragon kiln (a brick kiln, not a fiber kiln).
Shelf: Magnaform
Shelf release: Bullseye shelf primer
Glass: Bullseye Thin transparent colors capped with Bullseye Clear in 4mm thickness. Decorated with a few stringers on top.
Diameter of blanks: 4" to 10"
Fusing cycle:
300 degrees F to 1250 hold 40 minutes
9999 degrees F to 1500 hold 15 minutes
9999 degrees F to 960 hold 40 minutes
200 degrees F to 710 hold 1 minute.
After cycle, keep the door closed. Do not peek until the kiln reaches 200 degrees F.

On earlier firings for which I kept the hold time shorter at 1250, I was getting one or two oblong bubbles. I fixed these by grinding into the holes from the bottom of the blank with a dremel tool with a narrow diamond surface grinder, while squirting the grinding point with water to keep everything cool and lubricated. My husband showed me how to do this with a syringe of water in one hand, the dremel tool in the other. Then I refired with the above schedule and the oblong bubbles filled in nicely.

Keep in mind that I came up with this schedule through trial and error. Your best cycle may be different than this. I keep a notebook on my worktable and every time I do a firing, I note the following in the book:

1) Glasses used (including production date and sheet number)
2) Size and shape of layup (including which pieces were on top and which on the bottom)
3) shelf release or paper
4) shelf material
5) fusing cycle
6) RESULTS. After taking the piece out, I note anything that was less than ideal: number and shape of bubbles, surface problems, sticking problems. Then I propose changes for the next time I do a similar firing.

This recordkeeping has been essential to developing successful methods for my pieces in my kiln. Other people can give you ideas for solutions, but only you can be the expert on your pieces in your kiln. I firmly believe that recordkeeping and reflection are the most important tools you can use to develop a successful method.

You may already be doing lots of recordkeeping--this little lecture is not directed toward you personally, but for the possible benefit for newbies that are seeking information here on the board to fine-tune their fusing practices. Get ideas for solutions from others, but rely on yourself to test the ideas and judge if the solution is the correct one for you.

Ok, I'll get off my soapbox now--I don't know what came over me!

Good luck--I know you can solve this problem, one way or another!

Mary Kay