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Pattern Bar: Flow Slab

For discussion and commentary regarding the Lesson and Project videos of the Bullseye Kiln-Glass Education Online program.

Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Fri Apr 06, 2012 8:59 am

Hi Jennifer,

How frustrating to have a crack in your piece! Here are some questions that will help us identify the problem.

About the crack: Can you post a photo? To show up properly on the Forum it will need to be a fairly small file size. If you have trouble with this, send me your photos by email and I will post them.

What size is your kiln in relationship to the project? Can you tell us the interior dimensions of the kiln, and possibly the make and model? It would help to know where the elements are located in relationship to the project.

What glass styles did you use? (The style numbers are more informative than the color name.)

What material are your dams and kilnshelf?

Mary Kay
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Re: Pattern Bar: Flow Slab

Postby jennifer » Fri Apr 06, 2012 1:59 pm

Mary Kay,

Thanks for your response. In looking up the glass colours you asked for, I think that I may have inadvertently included a piece of non-fusible glass, which, of course, answers my question about why I have a crack. I feel pretty silly now!

But part of my question still stands - my mould, made out of cut up 1" thick mullite kiln shelves, lined with fiber paper and supported by more cut up kiln shelves, was 25cm x 25cm x 3 cm. That gave me 1875 cu cm. Multiplying this by the 2.5 spec grav. of the glass would mean I should have used 4687 gm of glass. The 2 stacks of 3mm glass, 14 layers high, each layer being 22.5cm x 5cm, only weighed about 2500 gm and there was just no more room for any more glass in the mould if I still wanted some movement in the final slab. I'm not sure I could have fit 4687 gm in there! Am I calculating incorrectly or does the formula not work well beyond some measurement?

Jennifer
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Mon Apr 09, 2012 10:40 am

Hi all,

I am posting some images on behalf of Aline Peterson, who is working on a Flow Slab project after viewing the video. She writes:

I have been working the Flow Slab Technique. Just came in from cutting the
slabs into slices, as I continue some of my questions are answered. I wanted
to post photos of my progress.


Aline, these are great process shots! There are pieces of broken glass on the floor in your final photo below. Did the piece break? Please contact me via email if you can't get into the Forum and I will post questions and any answers in this thread. Thanks for the photos!

Mary Kay
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Mary Kay Nitchie
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Re: Pattern Bar: Flow Slab

Postby jennifer » Mon Apr 09, 2012 11:44 am

Those are lovely flow slab slices made by Aline! Can I ask a question? How large was the mould? And how many grams of glass were used? I'm still having difficulty understanding how I could have fit 4687 gms of glass in a 25cm x 25cm x 3cm mould as per my last post.

Jennifer
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Mon Apr 09, 2012 3:23 pm

Posting for Aline:

I was about to finish cleaning up the edges and the piece slipped out of my hands as I was turning it. Then I discovered my finger tips were numb. I sent you the photos within 30 minutes. I could not comment as I was a bit speechless and heartbroken.

To Jennifer – Thank you for your kind words. The uneven stack was approximately 2.2 kg, a little more than the video. My glass cut into strips 2” x 8 1/2”, 30 pieces total, this size was a total guess. The space frame was 18 cm x 26 cm, again very close to the video. The slab seemed thinner than the expected 2 cm. I kept pretty specific notes if you need more information.


Aline, so sorry about the mishap! Are your fingers OK now?
Mary Kay
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Mon Apr 09, 2012 3:47 pm

Jennifer, here is advice from Jim re the amount of glass to put into the dams:

Jennifer should stack the glass higher to accommodate the amount of glass needed for her containment footprint for a final block 3cm thick. If it is higher than her dams, she should cut the glass to leave a half inch of space between the dams and her glass stacks. This will allow the glass to flow into the area without overflowing the dams. The glass will just roll into the space and settle out flat into the 3cm slab


I hope this helps!

Mary Kay
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Mon Apr 09, 2012 3:49 pm

Bridget, here is advice from Jim regarding your question:

If you are designing a final slab to be a specific width, add about an inch to the width when you cast the slab to accommodate for the coldshop. You will need to remove the separator materials from the perimeter of the slab to eliminate any residual primer/fiber from the equation. I generally cut about a half inch off of the slab perimeter to account for this. So if your final part needs to be 5 inches long, cast a block at 6 inches and cut it back to 5 when you are removing the seperators


I hope this helps!

Mary Kay
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Mon Apr 09, 2012 3:50 pm

And, a post from Aline--

Mary Kay

Feeling returned pretty quickly, thank you for asking. I’m thinking of “Flow Slab Part Dues”. Stay tuned.
Mary Kay Nitchie
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Re: Pattern Bar: Flow Slab

Postby jennifer » Mon Apr 09, 2012 5:57 pm

Aline,
I'm so sorry about your broken flow slab. How discouraging!

Jim,
Your response helped a great deal. I guess I'll just overcome my concern about stacking too high. Do you have to lengthen the soak at process temperature if your stacks are particularly high?

Jennifer
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Re: Pattern Bar: Flow Slab

Postby marykaynitchie » Tue Apr 10, 2012 11:57 am

Hi Jennifer,

Your question:
Do you have to lengthen the soak at process temperature if your stacks are particularly high?


Jim's reply:
That is an excellent question about soak times. The short answer is possibly. If you are asking a taller stack of glass to move into a containment system and flatten out it will generally take more time than a shorter stack of the same volume of glass. You’re simply asking the glass to move more. I would recommend being present during the process temperature of the fusing to check on the progress of the casting. The firing schedule we used for the video had a hold time appropriate for the amount of glass laid up in that particular configuration. Changing the variables will affect the amount of time needed to perform this casting function. If you are present during the firing you may find that you may need more time to flatten the slab. Conversely, you may also find you need less time to cast the slab flat in which case you can advance the schedule to annealing before the allotted time is up. This will lessen the cumulative heatwork you are subjecting the glass to.

We recommend documenting the variables of each firing for your records. As you get proficient with different layups you will be better able to predict which hold times to use. A little experience with this process and you’ll find it to be fairly predictable (while still “wowing” customers and fans of your work). On a side note, and as a fun challenge, every time you change the level and placement of the stacks make a little sketch to “guess” what the internal pattern will be. I think after a few slabs you will be able to figure out how to design a block fairly precisely to your design needs.

Have fun and best of luck,

Jim


Ditto (re: fun)!
Mary Kay
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