New to Fusing with somewhat disasterous results.

[jddiebolt]

Recently bought a kiln to start fusing and slumping, been doing stained glass for 3 years. My results are less than desired. First fire was OK but learned about having to have "layers" to get a proper fuse. Using Sys96 glass but did a compatability fire on Spectrum cathedrals. Came out real good with little or no stress. Used 96 suggested fire schedule. Second fire was a disaster. Larger pieces sticking to shelf. 96 clear thin sandwich, 12" dia. with frit and noodle in the middle, cracked in hundreds of pieces. 96 opal green & thin clear sandwich with scattered pieces of red opal in the middle. Cracked in a few pieces. I understand the cracking was on cooling because the edges are sharp. Cleaned shelf and recoated with Permo Primer. Next fire, sticking to shelf again. The pieces that have stuck seem to be taking small bits of shelf with them because it is no longer smooth like it was. Also ever piece that was fired has alot of kiln wash stuck to the back of the piece. Fusing temperatures have been between 1400 and 1465. Any suggestions would be appreciated.

[Paul Tarlow]

Kiln wash sticking to the backs of pieces -- after going to full fuse -- is not unusual. There are a number of ways to remove it. Soaking in CLR (available at the grocery store in the cleaning section) and then scrubbing gently with a Scotch 3M pad is one way. Be careful - the pads can scratch glass -- but if you use CLR you won't need mutch (if any) elbow grease.

I'd like to hear more about 1) how you did the compatibility test and 2) what your firing schedule is.

Hang in there -- stuff goes wrong for all of us at some point. Prior to this week I had NEVER had a piece thermal shock in the kiln. In the last three days it has happened twice -- with schedules I've been using for over a year. Go figure.

- Paul

[Joanne Owsley]

Hmmm, must be a bad glass week. I've had lots 'o stuff go wrong, too.
jddiebolt, what kind of kiln are you using? Does it have a controller? What firing schedule are you using?

[charlie]

Kiln wash sticking to the backs of pieces -- after going to full fuse -- is not unusual. There are a number of ways to remove it. Soaking in CLR (available at the grocery store in the cleaning section) and then scrubbing gently with a Scotch 3M pad is one way. Be careful - the pads can scratch glass -- but if you use CLR you won't need mutch (if any) elbow grease.

clr can discolor or fog certain glasses. i've had good luck using a single edge razor blade to get most of it off, then a plastic mesh dish scrubber.

I'd like to hear more about 1) how you did the compatibility test and 2) what your firing schedule is.

Hang in there -- stuff goes wrong for all of us at some point. Prior to this week I had NEVER had a piece thermal shock in the kiln. In the last three days it has happened twice -- with schedules I've been using for over a year. Go figure.

- Paul

thermocouple drift?

[Paul Tarlow]

thermocouple drift?

Hmmm. Maybe. How does one test for that?

I only glimpsed in the kiln this AM -- it was still pretty hot. I need to confirm that it broke on the way up (the first piece did).

I didn't get a good look at edges -- but the thin fire seemed undisturbed. I'm thinking if the piece broke after the thin fire binders burned out that the thin fire "dust" would have been moved about.

The weird thing is that both pieces that broke last night split almost perfectly straight in the middle.

- Paul[/quote]

[charlie]

thermocouple drift?

Hmmm. Maybe. How does one test for that?

you have to measure it against a known good standard, either another thermocouple known to be accurate, or against something like boiling water and ice. even that isn't good sometimes since the drift can be non-linear (ie the hotter it gets, the higher percentage it drifts).

if something stops working, you look at what is changing. glass, seperators, environment, kiln, thermocouple, controller.

the thermocouple is about the only thing in the list that changes over time besides environment.

[Bert Weiss]

thermocouple drift?

Hmmm. Maybe. How does one test for that?

you have to measure it against a known good standard, either another thermocouple known to be accurate, or against something like boiling water and ice. even that isn't good sometimes since the drift can be non-linear (ie the hotter it gets, the higher percentage it drifts).

if something stops working, you look at what is changing. glass, seperators, environment, kiln, thermocouple, controller.

the thermocouple is about the only thing in the list that changes over time besides environment.

I'm not an expert here, but I don't trust the freeze thaw thing as a test for a type K thermocouple. We really care what is happening at 1000º F not 32.

The test to do is a slump test. EVERYBODY ON THIS BOARD should do this to verify anneal soak temps for your kiln and thermocouple. I have written the directions for this several times on the board. I got it from Lundstrom Book 1. This test tells you the real deal for your setup not just a generic one.

[Bob]

I only glimpsed in the kiln this AM -- it was still pretty hot. I need to confirm that it broke on the way up (the first piece did).

The weird thing is that both pieces that broke last night split almost perfectly straight in the middle.

- Paul

Hey Paul,

Was this the first firing or had the pieces previously been fired? If the latter it could be that the piece wasn't properly annealed from the initial firing. Were you trying anything unusual or "heroic" in the initial firings? If so the problem may be with the initial firings and not with the firing that resulted in the breakage. Glass constant thickness? Were you slumping?

Maybe your kiln is overworked and just wants a holiday.

Cheers,

Bob

[Rob Morey]

Second fire was a disaster. Larger pieces sticking to shelf. 96 clear thin sandwich, 12" dia. with frit and noodle in the middle, cracked in hundreds of pieces. 96 opal green & thin clear sandwich with scattered pieces of red opal in the middle. Cracked in a few pieces. I understand the cracking was on cooling because the edges are sharp. Cleaned shelf and recoated with Permo Primer. Next fire, sticking to shelf again. The pieces that have stuck seem to be taking small bits of shelf with them because it is no longer smooth like it was.

jddiebolt

Yes it is normal to have kiln wash stick to your work. Opals are worse than transparents. A couple of alternatives are to fire on top of clear irid, with the irid facing down or you can use fiber paper or thin fire.

It is not normal to have you work stick to the shelf. The cracking sounds like thermal shock. Which means you came down too fast. Check your firing schedule. If it's not thermal shock then it could be from the glass sticking to the kiln shelf. As the glass cools it contracts a little and if there is some area that is stuck then POP! Do you sand your shelves smooth before you apply the kiln wash before each firing? If they are rough then you need to do that. How many layers do you apply? Do you apply it in many thin layers or in a couple of thick layers? You should apply a lot of thin layers; allow the wash to dry a little between each layer. Do you allow the kiln wash to fully dry or fire it to 250 and then cool down before you put you glass down and start to fire? You should do that too.



Don’t get too disappointed or frustrated at this point. We all have made mistakes and we all have our share of disaster stories. You are doing the right thing by asking questions here on this board. Read as many books as you can get your hands on. Brads book is probably the best. Check the archives before asking a lot of questions. It will save you lots of time and you will get to know who really knows their stuff. If you can’t find the answer there, then ask. People here are very generous with their knowledge and are willing to help. Just keep trying.

Good luck

Rob