Slumping run gives slight "milkiness" to glass

steve_hiskey · Post by **steve_hiskey** » Sat Nov 01, 2003 3:24 pm

I would love it if someone would help me out here.

Bulleye glass, coe90, 2, 3, or more layers thick.

first run (melt): glass is perfectly clear

second run (slump), glass on the edge of the bowl (where it stretches) gets a slight milkiness.

Barlett controller:
200deg/hr to 900
150deg/hr to 1200, hold 10
9000deg/hr to 960, hold 45
20/hr to 720, hold 10
off

Only the edges have the milkiness... the center of the bowl is perfectly clear.

I have been trying to get the MINIMUM temp to slump, because I am working with textures... can I do something like quickly jump to 1400 for a tiny amount of time to melt the outside?

thanks!

Steve

Tony Serviente · Post by **Tony Serviente** » Sat Nov 01, 2003 4:09 pm

An image would be useful Steve, expecially a close up of milky area. There are a few problems with going up to 1400. Unless your kiln is turbocharged, it will take a while to get up that high, and the glass is moving all the time. The glass will want to pool in the bottom of the form, and the sides will either decrease in height, and/or fold inward. Not only that, but you will pick up any texture from your form. Besides, it does not sound to me like that would even help. Are you using clear iridized? Did you use any kind of overglaze? Did you clean the glass well?
Is milkiness on inside or outside?

Luiza · Post by **Luiza** » Sat Nov 01, 2003 4:50 pm

Tony Serviente wrote: The glass will want to pool in the bottom of the form, and the sides will either decrease in height, and/or fold inward. Not only that, but you will pick up any texture from your form.

Hi Tony
If the slumping process is done at lower temps the decrease in heigh will not happen? Maybee 1200 F will prevent it?
Thanks
Luiza

Tony Serviente · Post by **Tony Serviente** » Sat Nov 01, 2003 5:20 pm

Luiza-
1200 was as high as Steve went the first time. He wanted to know if 1400 would fix the milkiness on a second slump firing. I think it would cause more harm than good.

Luiza · Post by **Luiza** » Sat Nov 01, 2003 5:32 pm

Tony Serviente wrote:Luiza-
1200 was as high as Steve went the first time. He wanted to know if 1400 would fix the milkiness on a second slump firing. I think it would cause more harm than good.

Hi Tony
I understood , but as you spoke about the height - and I am trying to slump a 15in disc and have a 15 in bowl without success, I thought maybee the lower temps would solve it...
Is it possible?
Thanks
Luiza

Tom White · Post by **Tom White** » Sat Nov 01, 2003 10:28 pm

Luiza, the basic principal of slumping glass is that if you are not using a drop out mold you are only softening the glass so that it conforms to the shape of the mold beneath it without stretching the glass. A bowl mold 15" across the top by three inches deep would need a glass circle 21" in diameter to make a glass bowl the full size of the mold. It is not possible to make a bowl as wide and as deep as your mold with a glass blank the same diameter as the opening of the mold. As that piece of glass softens and bends to the shape of the mold it slips down into the mold and becomes shallower and narrower than the maximum size of your mold. The glass is still 15" from edge to edge if you measure along the curved shape.

Best wishes,
Tom in Texas

bskirwin · Post by **bskirwin** » Sun Nov 02, 2003 12:20 am

I also just had that problem, with a disc of clear ( 15 " in diameter) with a second layer of colored transparent fused on top, all BE 90 COE, and after the slump to 1225, it came out with the bottom perfectly clear but the slumped rim milky, not devited, just milky. This has never happened before, using the same glass and mold..... Barbara

steve_hiskey · Post by **steve_hiskey** » Sun Nov 02, 2003 12:46 am

Are you using clear iridized? Did you use any kind of overglaze? Did you clean the glass well?
Is milkiness on inside or outside?

No iridized
No overglaze (the stuff I use doesnt work until 1400 and causes milkiness below 1400

)
Yes, I clean the glass. I don't think it is the glass cleaner, because the center of the slump does not get the matte finish.
The milkiness is on the inside (non-form side)

I should be more clear. By "milkiness" I mean that the glass has a "matte" finish rather than a clear finish.

I don't have my wife's website FTP controls on this machine. I will post a pic tomorrow. this is my second post. it doesn't look like this site allows me to put images inside the post... right?

thanks!

Steve

Brad Walker · Post by **Brad Walker** » Sun Nov 02, 2003 1:11 am

Are these stretch marks or mold marks from the slumping? Usually these form along the underside edges of the glass where it starts to stretch down the mold. They're much more likely on clear, and are usually caused by slumping too quickly.

steve_hiskey · Post by **steve_hiskey** » Sun Nov 02, 2003 1:30 am

the milkiness/matte-finish is on the inside. and I am slumping at 1200... just BARELY enough temp to get it to slump!

Luiza · Post by **Luiza** » Sun Nov 02, 2003 9:07 am

Thanks Tom
That was a silly question.

Luiza

PDXBarbara · Post by **PDXBarbara** » Sun Nov 02, 2003 2:05 pm

Did you fuse the blank with the clear down on fiber paper? If so, perhaps that's part of the problem. (I stress the word "perhaps.")

Last week I fused a piece with a piece of clear BE thin down on fiber paper (not thinfire). I'd planned to flip & slump with a polish.

As expected, some texture from the fiber paper. sanded edges, cleaned well. first slump was fine, except the texture had increased on the thin clear (now face up). sked: real slow ramps up... 50/hr from 1050. Slumped by 1100. jacked it to 1350 for a few minutes for polish.

Wanted more of a slump, so went to a deeper mold. Again, slow ramps up... still 50/hr to 1100. Then jacked to 1400 for several minutes. Result: slump fine, but surface clear very pebbly/pimply.. some stretch marks at edges (inside, just on the clear).

So, took the piece over to Bullseye for advice. Guess what? the texture was apparently devit, from doing the fuse with clear down on fiber. If I'd blasted the surface prior to slumping... no pimples, i'm told. Pretty weird to me, cause it wasn't scummy, and I was surprised that clear would devit so easily... 1 full fuse. This one is one of those classic mistakes that turn out way better than my original vision, though.... It's very cool, really. And I hope to replicate the mistake.

barbara

steve_hiskey · Post by **steve_hiskey** » Sun Nov 02, 2003 3:08 pm

Interesting. No, I dont user fiber paper. I didn't want to deal with the handling of it after firing. Just plain purple shelf primer. But YES, I am flipping the piece over for the slumping run.

I have dealt with devit before with chunks of glass that I bring home from glassblowing (everything that hits the floor has potential

) but I didn't think that bullseye coe90 stuff devit'd!

My standard fix for devit is to spray with the non-lead Fuse Master "Super Spray." But you have to get it above 1400 or you get milkiness from it too. I am worried that I will get texture on the surface due to the unevenness of the glass on the bottom layer.

I will give it a try. Thanks!

Steve

PDXBarbara · Post by **PDXBarbara** » Sun Nov 02, 2003 8:17 pm

Steve..
According to christy @ B.E., I'd have had a routine slump/fuse if I'd used kilnwash or thinfire. If I wanted to get rid of the "pimples" of devit, I'd blast it & then put it back in the wok.

Barbara

Barbara Muth · Post by **Barbara Muth** » Sun Nov 02, 2003 9:52 pm

That's probably it then... I have found with the flip and fire technique that it's easy to have scummed up the glass. So then I just blast and go.... Or avoid the problem by firing on thinfire which works fine if the piece isn't too big. The other day I got the creeping cracks from torn thinfire so had to fire again facedown on kilnwash and now I have to blast it.

Barbara

bskirwin · Post by **bskirwin** » Sun Nov 02, 2003 10:28 pm

I never heard of flipping over the piece from fuse to slump..... Is that to get rid of the texture on the bottom from the fiber paper....? But I usually only slump to 1200 degrees which is not fire polish temps.... I am confused. Barbara

steve_hiskey · Post by **steve_hiskey** » Mon Nov 03, 2003 12:10 am

I never heard of flipping over the piece from fuse to slump

I am playing with textures. bumps, trying to simulate ice. big textures and small textures. But you want the bowl to still be usable (smooth on the inside) afterwards, so you flip it over before fusing. You still get all the "optics" of the textures.

This requires a more controlled fire for the fusing run and a VERY controlled fire for the slumping.

If you are going "flat", you can go sit at 1500 and let everything melt. To keep the texture though, you have have lots more variables to play with.
Once you flip it over to slump it, you have to have as little temp as possible for the slump so that the inside of the bowl is smooth.

It is a lot of fun! try it!... you get all kinds of optics from a single piece of clear frit if it is a round "bump" because it catches the light and throws a shadow.

Steve

PDXBarbara · Post by **PDXBarbara** » Mon Nov 03, 2003 12:40 am

bskirwin wrote:I never heard of flipping over the piece from fuse to slump..... Is that to get rid of the texture on the bottom from the fiber paper....? But I usually only slump to 1200 degrees which is not fire polish temps.... I am confused. Barbara

Hi Barbara...
Yeah... that's one reason. Or, if you fuse "design side down" in order to hold the design rigid (you know how the top can get a little loosy goosy), you might flip & slump because you want the bottom to be the top. I do a version of what I learned from Brad's book... ramp up nice & easy & then go real real slow, like 50/hr from like 1050... in my kiln & depending on the size of the piece, slumping's happening by 1100. let it slump most of the way down, then ramp AFAP to 1350 or even 1400 for 5 minutes or less. Then crash to stop the action. it's usually worked pretty well for me.
Make any sense?
PDXBarbara