Why is this cracking? - WarmGlass.com

Why is this cracking?

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Sulie
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Why is this cracking?

Postby Sulie » Mon Oct 13, 2014 6:27 pm

I have spent the last few months slumping just one layer and now hope to progress a bit.. This piece is 6 mm thick, consisting of 2 layers of 3 mm Bullseye. As you see it cracked miserably. Looking through the forum I suspect that my first temp is too hot, though I got this schedule from a book. (sorry, cant recall which) The layers didnt fuse together, so I am at a loss.
Temps are C.
ramp @ 448 to 501 hold 40 min
ramp @ 508 to 650 hold 60 min
ramp afap to 516, hold 45 min
ramp afap to 370 hold 30 min

I know what a newbie question this is, but I'd be so grateful if someone could help me out and tell me where my mistake is. Additionally, I'd like to ask: when I get a correct firing schedule can I re-fire this piece, or must I trash it and start again?
Many thanks and greetings from Austria,
Sulie
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Marty
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Re: Why is this cracking?

Postby Marty » Mon Oct 13, 2014 8:32 pm

Sulie- First find that book, let us know who wrote it, then throw it out.
Next go here: http://www.warmglass.com/tutorial and check out the schedules, also in Brad's book, also on the BE website.

Basically, you're firing way too fast. You're inviting thermal shock on the way down as well- the afap ramp from 516C to 370C is brutal . You've also got to compensate for the black/clear issue.

Marty
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Re: Why is this cracking?

Postby Marty » Mon Oct 13, 2014 8:34 pm

One more thing- did you previously fuse the black and the clear before slumping?

Sulie
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Re: Why is this cracking?

Postby Sulie » Tue Oct 14, 2014 7:23 am

Hi Marty.. thanks very much! I didnt try slumping this, as this was my attempt to fuse before slumping.
I wasnt aware that there was an issue between black and clear; argh! The base is a white square, surrounded by black strips and then the whole thing is capped with a sheet of clear.
I have Brads book: I will read it again with better attention!
In your opinion, can I re-fire this with a correct schedule, or should I start over again with new glass?

Marty
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Re: Why is this cracking?

Postby Marty » Tue Oct 14, 2014 9:17 am

You can re-fire it but you'll see that circular crack. It could be a design element?!

Bert Weiss
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Re: Why is this cracking?

Postby Bert Weiss » Tue Oct 14, 2014 2:00 pm

That circular crack looks to me like a compatibility issue between the black and white glasses.
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Judd
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Re: Why is this cracking?

Postby Judd » Wed Oct 15, 2014 10:46 am

That was my first thought too. This is all compatible glass?

Bert Weiss
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Re: Why is this cracking?

Postby Bert Weiss » Wed Oct 15, 2014 11:01 am

Stresses from incompatibility tend to form around the perimeter of the 2 unhappy glasses. Stresses from annealing or thermal shock go across the interface and bend around.
Bert



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rosanna gusler
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Re: Why is this cracking?

Postby rosanna gusler » Wed Oct 15, 2014 1:30 pm

incompatible glass. r.
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Glass Fever
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Re: Why is this cracking?

Postby Glass Fever » Wed Oct 15, 2014 2:33 pm

S/he said the glass did not fuse together, you're still looking at separate sheets of glass, so not incompatibility. Simple thermal shock from ramping too fast.

Bert Weiss
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Re: Why is this cracking?

Postby Bert Weiss » Wed Oct 15, 2014 2:43 pm

Glass Fever wrote:S/he said the glass did not fuse together, you're still looking at separate sheets of glass, so not incompatibility. Simple thermal shock from ramping too fast.


That is not what a thermal shock crack looks like.
Bert



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Glass Fever
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Re: Why is this cracking?

Postby Glass Fever » Wed Oct 15, 2014 2:52 pm

Bert Weiss wrote:
Glass Fever wrote:S/he said the glass did not fuse together, you're still looking at separate sheets of glass, so not incompatibility. Simple thermal shock from ramping too fast.


That is not what a thermal shock crack looks like.


They say the glass didn't fuse together, the top temp was only about 1200 F. And from the picture it just looks like a sheet of clear sitting on top and the cracks are in the clear sheet. If there was no fusing than it can't be incompatibility, so that pretty much just leaves thermal shock, right? What else can it be?

Glass Fever
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Re: Why is this cracking?

Postby Glass Fever » Wed Oct 15, 2014 2:58 pm

I also would like to know were that weird schedule came from. The odd numbers make me wonder if it was translated from F to C, and maybe incorrectly.

rosanna gusler
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Re: Why is this cracking?

Postby rosanna gusler » Thu Oct 16, 2014 8:47 am

the schedule allowed for a tac fuse. that is a classic compatibility crack as far as i can see. i wouls suggest full fusing that same stack and will bet it breaks back apart. r.
artist, owner of wanchese art studio, marine finisher

Lori Schinelli
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Re: Why is this cracking?

Postby Lori Schinelli » Thu Oct 16, 2014 9:12 am

Ok . My 2 cents.
The white resists movement because it is so stiff. The black is very likely to move quickly. If the clear sheet tack fused to the underneath layer,you have one sheet of clear that is being pulled in 2 directions. I think the crack was caused by the viscosity differences between the white and the black

Bert Weiss
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Re: Why is this cracking?

Postby Bert Weiss » Thu Oct 16, 2014 11:00 am

Lori Schinelli wrote:Ok . My 2 cents.
The white resists movement because it is so stiff. The black is very likely to move quickly. If the clear sheet tack fused to the underneath layer,you have one sheet of clear that is being pulled in 2 directions. I think the crack was caused by the viscosity differences between the white and the black
Compatibility is a balance between viscosity and coefficient of expansion. They can both be different as long as there is a balance.
Bert



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Stephen Richard
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Re: Why is this cracking?

Postby Stephen Richard » Fri Oct 17, 2014 3:45 am

I agree with Bert, and think Rosanna's advice should be followed to determine if the glasses are compatible
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rosanna gusler
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Re: Why is this cracking?

Postby rosanna gusler » Fri Oct 24, 2014 10:33 am

so did you re cook it? r.
artist, owner of wanchese art studio, marine finisher

Andrea R
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Re: Why is this cracking?

Postby Andrea R » Sat Oct 25, 2014 1:42 pm

Bert Weiss wrote:That circular crack looks to me like a compatibility issue between the black and white glasses.

Was thinking the same cause thats a wierd crack!!
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Sulie
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Re: Why is this cracking?

Postby Sulie » Sun Oct 26, 2014 12:37 pm

Hi everyone and thank you so much for your opinions. I'm sorry to be so late in responding: I didnt see the additional posts until just now.
I didnt re-fire the cracked piece, but I made a second one using the same glass as before. I used a firing schedule that I obtained from the fusing video on Bulleye's channel on Youtube, and it came out fine, no cracking. Therefore it seems to me that the problem was indeed due to thermal shock.
The photo is a bit fuzzy, but I'm rather pleased that I was finally able to fuse and slump more than one layer of glass.... "baby steps"! Thanks to all who replied!
regards,
Sulie
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