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Pattern Bar: Flow Slab

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Re: Pattern Bar: Flow Slab

Postby lalalandglassstudio » Wed Jan 30, 2013 4:27 pm

Thank you!
cheers, Kirei
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Re: Pattern Bar: Flow Slab

Postby lsuder » Thu Jun 27, 2013 12:01 pm

I have made several opalescent flow slabs so far, but none have turned out as I wished. The first slab used almond striker, dusty blue and slate gray. Although they flowed nicely, the finished piece exhibited differing shininess between the colors. So, for the next several pieces, I fused a sheet of crystal clear glass on top of the slab slices. In each case, the piece shattered while cooling - even when using a conservative annealing schedule.

My most recent attempt used black and white opalescent in the slab; sliced 6 mm thick; 6 mm black border; 3 mm crystal clear on top (~9 mm total thickness). The piece was contained with within dams. Firing schedule was:

225/hr to 1225; hold 1:20
AFAP to 1490; hold :10
AFAP to 900; hold 4:00
27/hr to 800; hold :00
49/hr to 700; hold :00
162/hr to 75

(Note the annealing steps are as recommended by Bullseye for a 25 mm thick slab - just to be sure.)

Once again, the piece shattered badly. I am beginning to suspect that the clear glass is the culprit, although the firing schedule should have been within the bounds of Bullseye's compatibility testing. Or might the problem be the use of soft black glass along with stiffer glass?

Any and all thoughts on this will be appreciated. I will attempt to post photos later.
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Thu Jun 27, 2013 3:12 pm

Photos will help--the nature of the break will often narrow down the possible causes.

Could you list the style numbers of glass that you used? Was it all Bullseye?

What kind of kiln do you have? Describe the locations of the elements (top, sides, door, floor)

What size is your kiln?

What did you use for dams?

How far are the dams from the elements?

Also, if for some reason your kiln is not heating evenly, a longer anneal soak will not anneal the glass. You might need to run a "Knowing Your Kiln" test to see if there is a cold or hot spot in your kiln. (I'm not saying that this is the cause in your case. It is just one of the variables to check.)

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

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Re: Pattern Bar: Flow Slab

Postby lsuder » Fri Jun 28, 2013 4:47 pm

marykaynitchie@bullseyeglass.com wrote:
Photos will help--the nature of the break will often narrow down the possible causes.


Here's the before photo:
Image

After
Image


Could you list the style numbers of glass that you used? Was it all Bullseye?

It was all BE double-rolled glass. The flow slab was made from black and white 3 mm opalescent, sliced 6 mm thick. The border (seen in the photos) was 6 mm black. (Neither of the black pieces were stiff black. The top layer was 3 mm double-rolled crystal clear. I'll look up the style codes, but I think this description should be definitive.

What kind of kiln do you have? Describe the locations of the elements (top, sides, door, floor)
What size is your kiln?

Paragon Fusion 14, a top-fired 14" square kiln.

What did you use for dams?

Sawn pieces of kiln shelf, about 1/2" x 1" x 12" each. I used a narrow strip of 1/16 BE shelf paper inside of each dam.

How far are the dams from the elements?

The tops of the dams were about 3 1/2" from the lid, and the elements are recessed about 3/8 into the grooves in the lid. The glass was about 4" below the lid.

Also, if for some reason your kiln is not heating evenly, a longer anneal soak will not anneal the glass. You might need to run a "Knowing Your Kiln" test to see if there is a cold or hot spot in your kiln. (I'm not saying that this is the cause in your case. It is just one of the variables to check.)

While we have not run exactly that test, the kiln has seemed to fuse everything evenly, including when we have fused a number of small, similar pieces in different areas of the shelf simultaneously. The kiln is about 6 months old, and the elements are in good shape. I don't think uneven heating is the culprit.

I hope the photos provide some clues. Thanks for your help.

Thanks,
David

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Re: Pattern Bar: Flow Slab

Postby lsuder » Sat Jun 29, 2013 11:25 am

Hi, Mary Kay.

Here are the glass styles used in the failed flow slab pattern bar discussed and illustrated above:

    Black 3 mm: 000101-0030-F-1010
    Black 6 mm: 000100-0060-F-1010
    White 3 mm: 000113-0030-F-1010
    Crystal Clear Transparent 3 mm: 001401-0030-F-HALF

Thanks again for your help.

David
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Re: Pattern Bar: Flow Slab

Postby Twin Vision Glass » Tue Jul 02, 2013 10:31 am

It is in my opinion that it broke on the way up as you can see how the dams are pushed out and the glass has healed at the top. I myself will always go slow on the heat up of pattern bars . You also have black and white where black absorbs heat and white reflects which can create it's own problems. You are quite close to the outer side of your kiln, and I might suggest to scale down the size of the piece to not only give room to brace the dams , but for the glass to not be so close to the outer area of the kiln walls. Do you top elements span the complete area of the roof. It was a huge change also in the way I work the minute I got top and bottom firing and placed the piece in the center of the kiln with 3 inchs of room around outer kiln shelf for air flow.
Of course these are all just my ideas of how to work differently to be successful in pattern bar fusing .
Sincerely, Leslie (and I am so sorry for you loosing your piece.) :cry: (oh yes and the 1401 clear is a beautiful glass to work with . I use it all the time for my base as well as my capping. )
Leslie Rowe-Israelson
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Re: Pattern Bar: Flow Slab

Postby charlie » Tue Jul 02, 2013 2:46 pm

are the broken edges sharp or rounded?
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Re: Pattern Bar: Flow Slab

Postby lsuder » Wed Jul 03, 2013 1:08 pm

The photos I posted earlier didn't show it very clearly, but all of the broken edges were sharp. None were rounded. This piece, and a previous similar one, broke during the annealing. (In the case of the previous piece, I heard it break.)

Image

There are also a number of visible internal cracks that are not full depth.

Leslie, your point about the differences between the heat absorption of black and white is a good one. I had thought about that, and believed that I my firing schedule was conservative enough, but maybe I was wrong. I'm making this piece for a friend who likes black/white combinations, hence my choice of colors. Do you think it would make a difference if I used stiff black glass?

More likely, I think, your thoughts about the size of my piece relative to the size of the kiln are the key. There was a lot of thermal mass at the edges of the piece with not a lot of room for air circulation around the edges. Despite what I thought was a conservative annealing schedule, I expect the center of the piece cooled faster.

I know that, with flow slabs, we are pushing the envelope of Bullseye's testing of the glass. Maybe this combination of colors, along with the size of this piece relative to the size of our kiln, just won't work.

I would love to hear any other thoughts about the cause of this problem.

Thanks,
David
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Re: Pattern Bar: Flow Slab

Postby journeyamw » Fri Aug 30, 2013 1:57 pm

Hi What would the flow be like if you put a piece of clear glass on the bottom?
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Re: Pattern Bar: Flow Slab

Postby journeyamw » Sat Aug 31, 2013 12:33 pm

Hi from Canada
Can you tell me how much glass you used in cm or inches. I am cutting ad cutting and it seems lie a lot by weight, maybe my scale is off.
Thanks. Anne
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