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Cracking in Strip Construction

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Cracking in Strip Construction

Postby jett_grrl » Sun Jul 29, 2018 5:47 pm

Hi there, if anyone has any advice I would be greatly appreciative. In two weeks I have fired two separate pieces, both strip construction, both have cracked along the strips after slumping. I fired them both at 300 DPH to 1200, 2:00 bubble soak, then 600 DPH to 1500 for 20 minutes, AFAP To 900 for two hours, 100 to 700, then cool down to room temp. They were than slumped at 200 DPH to 1205 for 20 minutes, AFAP to 900 for two hours, 100 to 700, then cool down to room temp. Both are 3/8 of an inch thick. I am using a fairly new Scott GM 1414 count on 1 inch thick kiln shelves on 4 inch posts. Both cracked quite severely along the strip lines on the undersides Only. I have tried attaching photos but it says the files are too big. I have fired many other strip construction pieces successfully, including other pieces in both of these firings… I am losing my mind and just about ready to give up glass entirely. If anyone has any thoughts or advice that might be helpful I would be so grateful. I have examined every possibility and cannot come up with a single explanation. This actually happened another time in April, but I had numerous problems with some myrrini pieces cracking at the same time, and I thought it might have to do with overfiring of transparent orange and yellow’s. But in hindsight those cracks were in the black and the same cobalt blue that just cracked in this piece. Both slumping molds are seemingly perfectly primed... Help me please!
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Re: Cracking in Strip Construction

Postby jstahl956 » Sun Aug 05, 2018 4:55 pm

To post your photos you need to resize them. If you go to http//www.shrinkpictures.com this site is fairly easy to use to resize.

Would be curious to see the photos. Was this BE glass and if so what are the color codes of the glass used? What was the mold you were slumping into? Also, what is the size of the finished piece?
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Re: Cracking in Strip Construction

Postby ejgiebel » Thu Aug 09, 2018 9:48 am

My question would be what mold are you slumping into? I used the large retro party bowl mold (8936) for a pattern bar - segment slab and the glass pulled apart on the edges of the colors in the four edges in the deepest part of the mold. Deep cracks that were straight, not sharp and that did not extend all the way through the glass. I'm just wondering if the lines of the strip construction might be the issue if you're going deep.

I had done these before with great success, but never slumping into that deep of a mold. There's a post here with pictures, but I now fuse a piece of clear to the bottom of these before slumping and have never seen the problem again.

Also, the segment slabs are an opal/transparent pair, so if your strip is mixing transparent and opal, which shouldn't be a problem, that might be a contributing factor.

Oh, and when I posted my pictures, I shifted some plaster (flour would work) into the cracks to make them more readily visible in the photo.

FWIW
Ed Giebel
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