Help- fusers of LARGER (over 2’) pieces

[Bonnie Rubinstein]

Okay-we know glass is tricky. I am committed to conquering this issue…. I have had some recent breakages with large glass. After cooling , and all is fine, it breaks. The glass was 2’ x 3’ and 2’ x 4’; flat about ¼” to 3/8” thick. I use System 96, and wonder if anyone has consistent success (I used to; but not sure why I don’t now; and my schedule now is more conservative). I use a genesis kiln.

Yesterday, a piece was resting on it’s long side, against a board, someone slightly moved the board, and the glass just cracked (one long crack upward). We could not figure out why. It looks like the break may have started at the bottom, where the glass was alittle uneven and protruded out about 1/8”, but that should not have caused it.

Here was my schedule for fusing ( I also fired again at a lower temp for the tack fuse..and annealed the same schedule)
125 1195 30
75 1370 10
400 1385 20
full 1000 8
200 955 3hr. 20 min.
50 700 .15
400 120 0

Spectrum thinks since I am fusing so low, that my kiln may run hot, hence the anneal should be set lower. BUT in my smaller kiln, I also fuse at 1385. So, that may not be valid.

If you fuse large with system 96, please let me know your schedule and thickness, and input!

Thanks.

[DonMcClennen]

I think the problem may be as Spectrum suggests .. you pyrometer... I fire the size and thickness you are at 1480F.... 95F difference is substantial. I would slow down your ramp from 1000 to 950 as that's into the annealing zone(your using 200F I would use 50F to 80F max.)

[Bonnie Rubinstein]

will do .

thank you Don.

I am curious to know if more artists out there fuse large scale artwork??

I would like to get your input and also connect about it.. thanks.

[Barb R]

Bonnie,

I don't hold that long at 950. For 1/4" to 3/8" Spectrum says to hold 60 minutes. Sometimes I hold longer - but that's only if I have tack fused elements. I think that if there are some hotter and colder areas of your kiln, it's possible to introduce stress into your piece by holding that long at the anneal soak.

Barb

[Laurie Spray]

In have a Genesis and fire in it daily although only occasionally that large. But.....I would think it would be close to my 23" x 23" pieces......2 layer with some elements fused......
I anneal a piece that size 2 hours, 100 to 850 hold 30, 100 to 700 and off. My top temp for a full fuse is 1460 hold 10.

[Bert Weiss]

955 is way too hot. You are wasting that time. I would suggest lowering your anneal soak to no higher than 920. 35º can make a big difference. Your practice shows a definite problem. Either the inside of your kiln has widely uneven temperatures, or you are annealing too hot, too long. I'll put my money on too hot, and too long. For 3/8" uniform thickness float, I anneal soak for 1.2 hours and take the same to drop 100ºF. If you soak too long, the glass will equalize with the kiln. If the kiln is too hot, your real anneal is happening on the next segment. A quick anneal schedule at the too hot temp can work, as the glass is at a different temp than the air and is following along.

The myth that you can not anneal too long is really wrong, if you are at the wrong temp, or the glass sees uneven heat.

[Bonnie Rubinstein]

Thank you all for this input! this is an eye-opener, as when I have had issues in the past, I have heard 'anneal longer', but I can see that this would be problematic to anneal longer at the wrong temp!

I will readjust my schedule. I have another 2' x 3' piece in the kiln, that I need to fuse, and I was waiting for feedback.. thanks and I will cross my fingers.

re: spectrum schedules..I have not used them for years. I made my own, and until recently, these were fine.

Also, I need to repair the other piece, 2 x 3' with a clean crack upward from mid- bottom to the upper side. I can attach with superglue, and block the sides. Do I also add a clear thin piece all along the top of the crack to ensure repair?

I may take my pyrometer from my very small kiln and put it in the bigger to monitor temp. and look for discrepancies.

[rosanna gusler]

i would also do the know your kiln test for evenivity . r.

[Marty]

Bonnie- You should re-think your entire schedule. Many of us do large panels from 1/4" thick and up and have no issues. For a start please tell me why 75 1370 10, 400 1385 20? That makes no sense to me. 400 dph from 700 to a warm room temp is too fast- try 100 dph. What does 8 minutes at 1000 do? It's voodoo, but if it works for you (and you know why) that's fine with me.

[Bonnie Rubinstein]

I have so many notebooks of schedules through the years. This is what my most recent one is based on my own experience, and input and reading. I stop it at 1370 to watch how it is fusing, and then just bring it up to 1385 for full fuse... I believed ramping alittle faster after 1370 up another 15 degrees was acceptable.

I usually down at 400dph from 700 without issue; Spectrum says 300. But now that I have had breakage, I am re-assessing all of it, and will re-adjust.

[Barb R]

It seems to me if you are getting a full fuse at 1385 that your kiln is running hot. I normally get a full fuse at 1440 to 1465F on System 96 glass.

Barb

[Bonnie Rubinstein]

very possibly. I will be setting up a test today with another pyrometer.

[Bert Weiss]

Thermocouples are the device that degrades over time. The catch is this. As the thermocouple gets old, it reads a higher temperature than it does when it is new. To a point, this would make your problems less pronounced. So, if this is true, you are really anneal soaking way too hot.

There has been debate about my opinion, but I far prefer a thermocouple encased in inconel steel to one with an exposed tip. My thermocouples that installed in my big kiln around 1990 are finally showing their age. I noticed that a firing to 1480 with a 10 minute hold wasn't yielding the heatwork it used to. Exposed tip thermocouples have a relatively short life in the accurate zone.

I know of no reliable method to calibrate a controller. Cones read heatwork, not temperature. Boiling is way too low to matter to us. I think the pros have some sort of expensive device that can calibrate.

Annealing takes place within a range, so you have quite a bit of leeway. Stresses are relieved quicker at the lower end of the range than the upper. So, annealing too hot is more of a problem than annealing too low. 30º is a big enough discrepancy to cause failure.

[Bonnie Rubinstein]

That makes alot of sense, although disconcerting. We depend on the accuracy of these tools so much for the success of our hard work. I don't know how difficult it is to replace a thermocouple. But I will be testing mine later today.

I will be annealing at a lower temp from now on, as you recommended.. and dropping and holding at about 850, as well, as Laurie S. does. She uses the same kiln, and System 96. Couldn't hurt.

All this advice is really appreciated greatly.

[Bonnie Rubinstein]

Performed my test with a second pyrometer. It showed my kiln is running 16 deg. less than other, so it does run hotter. I will now anneal lower, at 930, and hold again at 775 and 600. I have spoken at length with Spectrum, and have a VERY conservative schedule to try- it will take 1 day, 3 hours to fuse(!) But I am not taking chances with this project.

I will be praying to the glass gods, as well. Time to be a pagan.