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Devitrification And Slumping Issues


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#1 shad

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Posted 19 January 2010 - 07:00 PM

Finally got my kiln and new electric outlets for it!!! Which explains my absence lately. Everything has been going wonderful for fusing and plates until lately and I am looking to the fusing gurus for advice.
I have a Paragon Fusion 8 kiln (17.5" wide and 11" deep). So far I have been using 96 glass and have been using the following firing schedules (these work consistently great for friends; however their kilns are 15" x 6"):
Full Fuse -
rate temp hold
300 1220 30
600 1465 10
300 960 40
100 800 0
Slumping -
rate temp hold
300 1250 15
300 960 60
150 800 0
I have started having 2 problems. The first is with devitrification. All of a sudden I seem to be getting it on most of the glass (and not on new glass - the same glass i have been using with excellent results). And the second issue has been with the slumping. I have been trying bowls (cereal bowl size) and my bowls end up about 1" deep. Tried my first drop ring this weekend, had it on 3 1/2" posts and the glass barely sagged, maybe 3/4".

Any words of wisdom? I received about 20 molds from family for Christmas and am itching to try them all.

#2 Dawnt

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Posted 19 January 2010 - 08:21 PM

I have lots of trouble with devit in my fiber kiln....not so with my brick one. Since the fiber kiln is the big one, and therefore fires the big expensive pieces, I've tried about everything to combat the problem! Have you changed how you clean the pieces before assembling and firing? Some glass cleaners can cause devit, so I've started using a 3 step cleaning process. First, I scrub with the spray foam type glass cleaner and a well washed bar rag, then rinse well with tap water, then do a quick dip and swipe in distilled water and dry the pieces well with a clean flour sack cloth. Make sure the cloths are washed in hot water only with no detergent.

I've got some vintage bullseye that is particularly prone to devit. I clean the hell out of it, then spritz with a devit spray consisting of borax dissolved in water. That seems to do the trick.

As for your slumps, you'll need to either soak longer or inch up the temps a bit to get more of a drop. I'd start with adding 5 or so minutes to your soak time. Then inch up to 10, and if that doesn't work, up your top temp by about 10 degrees with the initial shorter soak time.

Fun and frustrating, isn't it? Good luck!

Dawn

#3 shad

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Posted 19 January 2010 - 08:43 PM

O my - I feel I need a master's degree in glass! As for cleaning...I use a foam glass cleaner, then hot soap and water, followed by denatured alcohol and then hot tap water. I've not tried the flour sack cloths, I have been using the lint free ones for car glass. I have a devit spray but it says not to use on items that will be food bearing. Can you use the borax spray on a piece will be used for food?

I try the additional soak time this week and see if that helps. I love my kiln and the pieces up to this past couple of week have been gorgeous (they made everyone's Christmas) - and the size is wonderful. However I've noticed that my friends smaller kiln doesnt take nearly as long to fuse as mine does (my glass is in there about 20 hours from start to under 100 degrees). O well, I've never been one to take the easy path - hehe.

#4 Rebecca

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Posted 19 January 2010 - 09:36 PM

I can't help with the devit, but I keep peeking at mine until I have the slump I want. Then I go on to the cool down and annealing. Someone can tell you how to do that with a controller - I'm lucky I don't have one!

I'm using another piece of your drapery glass. Soon there won't be any left!

Rebecca

#5 shad

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Posted 19 January 2010 - 10:04 PM

O no! I need to get with you about that. I know you're 'just up the road' but I havent been able to head that way. We're working on a road trip though. The kiln has overtaken my glass room, my spare time, my life.......hehe.

#6 Dennis Brady

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Posted 20 January 2010 - 12:18 AM

Finally got my kiln and new electric outlets for it!!! Which explains my absence lately. Everything has been going wonderful for fusing and plates until lately and I am looking to the fusing gurus for advice.
I have a Paragon Fusion 8 kiln (17.5" wide and 11" deep). So far I have been using 96 glass and have been using the following firing schedules (these work consistently great for friends; however their kilns are 15" x 6"):
Full Fuse -
rate temp hold
300 1220 30
600 1465 10
300 960 40
100 800 0
Slumping -
rate temp hold
300 1250 15
300 960 60
150 800 0
I have started having 2 problems. The first is with devitrification. All of a sudden I seem to be getting it on most of the glass (and not on new glass - the same glass i have been using with excellent results). And the second issue has been with the slumping. I have been trying bowls (cereal bowl size) and my bowls end up about 1" deep. Tried my first drop ring this weekend, had it on 3 1/2" posts and the glass barely sagged, maybe 3/4".

Any words of wisdom? I received about 20 molds from family for Christmas and am itching to try them all.


I don't know where you go those schedules, but they are weird. You're getting devit because you have completely missed the part of the schedule intended specifically to prevent devit. From performance temperature (1465 for full fuse and 1250 for slump) you're dropping temperature at 300 dph. That should be AFAP (as fast as possible).

Here's the schedules I've been using for several thousand successful firings:

FULL FUSE
1. 400 dph 1000F hold 20 (equalized temperature)
2. 850 dph 1465F hold 20 (completes fuse)
3. AFAP 960F hold 60 (anneal)
4. 400 dph 300F OFF

SLUMP
1. 400 dph 1000F hold 20
2. 850 dph 1250F hold 20
3. AFAP 960F hold 60
4. 400 dph 300F OFF

Ramp speed up and down depends entirely on glass thickness.

There's a variety of kilnforming tutorials on Glass Campus I suggest you read. I especially recommend "Kilnforming Kindergarten". I even more strongly recommend you stop using those weird firing schedules,

http://www.glasscampus.com

You should be getting an adequate sag at 1250F. Try a longer hold. Increasing the hold time produces the same results as increasing the temperature but with much lower risk the glass will distort. It's possible your kiln isn't actually getting as hot as it's reading. Here's how to test:

1. Cut some square pieces of glass. A 2" square, a 1 1/2" square, a 1" square, and a 3/4" square.
2. Stack the pieces in a pile in descending size (make pyramid)
3. Fire to the 1350F with a 15 min hold (use the same schedule I gave you for full fuse but switch from 1465F to 1350F at top temperature.
4. If your kiln is producing an accurate 1350F, you will have all 4 pieces tack fused together with no change to the edges of the pieces other then the razor edge very slight softened.

Now, try exactly the same experiment and fire to 1400F. You should have a contour fuse (check Spectrum's website to see the shape it should be).

#7 Dawnt

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Posted 20 January 2010 - 06:29 AM

I read on the warmglass boards once that alcohol can cause devit. Try eliminating that. AND....as Dennis said, AFAP from top working temp to annealing temp. Sometimes, with the bigger kilns, AFAP isn't really all that fast, (hence your longer firing times), so you need to take some extra steps to avoid devit on that ramp down. If you have a vent, you can also try turning it on during the ramp down to speed up the temperature drop a bit.

No...you shouldn't use the borax spray if the glass will be food bearing. I avoid using it unless I'm working with the old cranky glass.

It seems complicated, but is really just a matter of getting to know your kiln. :hypnodisk:

I don't know if your controller allows you do edit on the fly, or pause your program, but if it does, don't be afraid to peek in the kiln to see if you need to add a bit of time for your slump. It won't hurt anything to crack it and take a look at top temp. (Be careful not to singe your eyebrows, though!)

#8 shad

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Posted 20 January 2010 - 08:59 AM

Goodness I have a lot to read and think about. I can't wait to try out some of these suggestions. Thanks so much for all the help. I will be sure to keep you informed on my progress (success that is!).




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