What happens in a full fuse in a slumping mould? - WarmGlass.com

What happens in a full fuse in a slumping mould?

This is the main board for discussing general techniques, tools, and processes for fusing, slumping, and related kiln-forming activities.

Moderators: Tony Smith, Brad Walker

Post Reply
Mike H.
Posts: 7
Joined: Sun Mar 16, 2003 3:57 pm
Location: Maui HI

What happens in a full fuse in a slumping mould?

Postby Mike H. » Tue Apr 29, 2003 4:08 pm

I have been told that I probably shouldn't re-fuse a piece flat,that has been fused & slumped(variations in thickness issue).Can I fuse to about 1400 to fire polish in the orignal
mould without any thing weird happening,What should I expect?
Mahalo.....Mike

Brad Walker
Site Admin
Posts: 1348
Joined: Fri Mar 07, 2003 9:33 pm
Location: North Carolina, USA
Contact:

Postby Brad Walker » Tue Apr 29, 2003 4:20 pm

Despite what you've been told, I would refuse flat rather than try to reslump in the original mold. Assuming a bowl-shaped mold, if you refire to 1400, the glass will slip down the sides and you will probably get some buckling and such in the bottom. The shape will definitely change.

Refiring to flatten the piece will give you a flat shape again, which you can then re-slump at normal slumping temperatures. The main thing to watch out for are devitrification (don't spend too long above 1300F or use a devit spray). You will lose or change any existing texture on the re-fuse -- if differences in thickness is an issue, just fire slower on the re-fuse firing.

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Tue Apr 29, 2003 4:35 pm

Yes, Brad has given you sound advice. I have flattened, then reslumped bowls many times. There is lots of information on this Board, but it's not all good. You have to learn to assess it.

Interestingly, here is one of the topics from the upcoming BECon:

Internet Education in Glass: Is Lunch Really Free?
How much can you learn about glass on the internet?
How do you assess what you're getting?

Brock
My memory is so good, I can't remember the last time I forgot something . . .

Tony Smith
Posts: 1037
Joined: Sun Mar 09, 2003 5:59 pm
Location: Massachusetts, USA
Contact:

Postby Tony Smith » Wed Apr 30, 2003 7:01 am

I think it's important for people to realize that, depending on the shape of the original slump, how steep the walls of the mold were and how much the glass stretched, the flattened glass may not return to its original shape when flattened.

The best advice is to try it, and see for yourself. You will see which shapes can be successfully flattened with minimal distortion, which shapes require manipulation in the kiln to straighten out wrinkles, and which give you new and interesting shapes to work with.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 9:07 am

The glass should not have stretched at all slumping into a mold, just changed it's plane. Have you had it stretch, then refuse to return to it's original shape, when you have attempted this, Tony?
My memory is so good, I can't remember the last time I forgot something . . .

Tony Smith
Posts: 1037
Joined: Sun Mar 09, 2003 5:59 pm
Location: Massachusetts, USA
Contact:

Postby Tony Smith » Wed Apr 30, 2003 9:16 am

Yes. I have a ceramic ripple-edge mold that has a fairly steep side wall. After deciding I didn't like the shape of the piece, I tried to flatten it... the glass wrinkled where the wall was. Perhaps a lower temperature and a longer hold would have prevented this... or maybe inverting the piece during the flattening attempt. I'm not sure. Since it it didn't work the first time, it wasn't something I was going to try again with that mold.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 9:26 am

Well I hardly find one try conclusive. I think you have illustrated the schism between research and knowledge. Brock
My memory is so good, I can't remember the last time I forgot something . . .

Phil Hoppes
Posts: 297
Joined: Wed Mar 12, 2003 2:20 pm
Location: Overgaard, AZ

Firepolish

Postby Phil Hoppes » Wed Apr 30, 2003 9:34 am

You shouldn't have to go as high as 1400 for a nice firepolish. I'd ramp at what ever safe speed is required for the thickness of your piece up to 1000F and then go at 400dph to 1300 with about a 5 min hold and then anneal. You should get a nice firepolish.

Phil

Tony Smith
Posts: 1037
Joined: Sun Mar 09, 2003 5:59 pm
Location: Massachusetts, USA
Contact:

Postby Tony Smith » Wed Apr 30, 2003 10:24 am

Brock wrote:Well I hardly find one try conclusive. I think you have illustrated the schism between research and knowledge. Brock


My point was that flattening a piece doesn't always work. Since it's a process that you would only use to salvage a piece, it's fair that people know that.

I don't understand why you believe that illustrates a schism between research and knowledge.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 10:38 am

Well I think your response would deter people from trying. From doing it many times I can assure people that it works, most, if not all, of the time. In your case, where the glass stretched, all you had to do was go a little hotter, or stay hot a little longer, and your piece was salvaged.

The difference is experience. I have done it many times. The result you get from one try may not be indicative of the result you could achieve with practice. Does that make sense to you?

Brock
My memory is so good, I can't remember the last time I forgot something . . .

Glenda Kronke
Posts: 64
Joined: Tue Mar 11, 2003 11:44 am
Location: Austin, TX
Contact:

Postby Glenda Kronke » Wed Apr 30, 2003 10:42 am

Please stop.
Thanks

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 10:52 am

Please stop.
Thanks

Please stop what?
An open and frank discussion of techniques and results?
What's the problem?
Brock
My memory is so good, I can't remember the last time I forgot something . . .

charlie
Posts: 961
Joined: Mon Mar 10, 2003 3:08 pm

Postby charlie » Wed Apr 30, 2003 11:03 am

Brock wrote:The glass should not have stretched at all slumping into a mold, just changed it's plane. Have you had it stretch, then refuse to return to it's original shape, when you have attempted this, Tony?


yes, it has to change shape.

the outside of the glass has to grow, since it is in tension on the curve, the inside has to shrink, since it is in compression, unless the glass is infinitely thin.

say you're slumping into a ball mold, where the ball has a radius of 12". if the glass is 1/4" thick, the back surface is a radius of 12". the top surface takes the shape of the mold, and thus has a radius of 11.75". unless the edges changed shape, that extra glass on the top surface has to go somewhere. either the thickness changes some, or the shape changes some, over the distance of the glass blank.

when it's flattened, it can't go back to the original shape. it'll change somehow.

and yes, i've had things change shape when reslumped back flat.

Phil Hoppes
Posts: 297
Joined: Wed Mar 12, 2003 2:20 pm
Location: Overgaard, AZ

Not having tried this but thought about it

Postby Phil Hoppes » Wed Apr 30, 2003 11:15 am

I agree with you Charlie but to Brocks point for certain shapes and sizes it will probably work fine IF you go slow enough at the right temp. There in lies the key I'm guessing. To get the best results I'm guessing you probably have to go pretty slow to allow time for the glass to deform and reflow. If you had 6 copies of the same piece you could probably experiment to find the right one. Or, if you just practice one will learn over time what is the right setting to use for different shapes. Square and rectangular objects I'm betting work much better at this than round.

Phil

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 11:15 am

I can't argue with your theory Charlie, but I have repeatedly done this, and to the human eye, there is no difference when re-flattened after slumping. I have done it mostly on bowls with geometric designs where, if the blank does not perfectly slump to the bottom and exact center of the mold, I cannot properly finish the edge.

Flatten, re-slump, properly . . . voila.

Brock
My memory is so good, I can't remember the last time I forgot something . . .

lyndasglass
Posts: 21
Joined: Wed Apr 23, 2003 6:41 pm
Location: Salem Oregon
Contact:

Postby lyndasglass » Wed Apr 30, 2003 12:15 pm

I think this is an interesting discussion. I have re-flattened and refused. Most of the time I believe is has worked fine. Mostly when I have a problem that would make me want to do this, I assume that the glass is already used/wasted and any salvage effort i can make would be ok with me. Sometimes I think we need to let go of our expectations and let the glass take us where it wants to go. ( I don't really mean to sound cosmic, but I think sometimes the unexpected can leads us to new avenues)

Plus, anything we try, adds to our learn "bank"

Just my .02 worth,
Lynda

Mike H.
Posts: 7
Joined: Sun Mar 16, 2003 3:57 pm
Location: Maui HI

Thanks to all

Postby Mike H. » Wed Apr 30, 2003 1:44 pm

I appreciate the input.
I will refuse flat rather than in the mould,and go relatively slow
and expect (exactly) what everyone said!!!! :)
Mahalo.......
Mike

Brock
Posts: 1519
Joined: Mon Mar 10, 2003 1:32 pm
Location: Vancouver, B.C.

Postby Brock » Wed Apr 30, 2003 1:49 pm

I developed the Craig Shuffle, (where I reach into the kiln, pick up the loaded mold, and shake it around to center the blank perfectly) in response to problems I was having with slumping into woks. Beats flattening and re-slumping. Also, try a small bevel on the bottom edge of your blank, right where the side meets the bottom. Doesn't have to be big, a few passes with a 220 belt on a WBS should give you a 1/32 to 1/16 bevel, which will help considerably, in facilitating an even slump down the mold. Brock
My memory is so good, I can't remember the last time I forgot something . . .

Tony Smith
Posts: 1037
Joined: Sun Mar 09, 2003 5:59 pm
Location: Massachusetts, USA
Contact:

Postby Tony Smith » Wed Apr 30, 2003 7:57 pm

charlie wrote:yes, it has to change shape.

the outside of the glass has to grow, since it is in tension on the curve, the inside has to shrink, since it is in compression, unless the glass is infinitely thin.

say you're slumping into a ball mold, where the ball has a radius of 12". if the glass is 1/4" thick, the back surface is a radius of 12". the top surface takes the shape of the mold, and thus has a radius of 11.75". unless the edges changed shape, that extra glass on the top surface has to go somewhere. either the thickness changes some, or the shape changes some, over the distance of the glass blank.

when it's flattened, it can't go back to the original shape. it'll change somehow.

and yes, i've had things change shape when reslumped back flat.


One way to visualize the problem is to cut a piece of paper the shape of your unslumped glass and place it in your mold. Paper will not stretch without tearing so it works well for this model. If the paper can follow the contour of the mold, then the glass doesn't have to stretch or thicken when it slumps. It would be fair to consider this as a simple bend in the glass. If the paper wrinkles or needs to be folded to match the contour of the mold... or no matter what you do to the paper, it won't match the contour of the mold, then the glass must stretch or thicken when slumped.
If you place a number of slits in the paper going through the center (but not all the way to the edge), and contour the pie shaped pieces to the mold surface, you can see how much your glass has to stretch to fill the open spaces.
Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun

Lynne Chappell
Posts: 186
Joined: Fri Mar 14, 2003 2:05 am
Location: Surrey B.C. Canada
Contact:

Postby Lynne Chappell » Thu May 01, 2003 1:38 am

I've flattened slumped shapes a few times, more or less successfully. After flattening, I added glass and refused and then reslumped. (Can you tell that something awful had happened on the slump? Like I peeked too long and cracked it?) These were fairly shallow bowl shapes, and the biggest problem was that the flattened shape was now larger than the original. The design wasn't all that distorted, but it would be bigger. One piece was pretty much as big as it could be for the mold, so after reflattening, I had to find another mold.


Post Reply

Return to “Techniques and Tools”

Who is online

Users browsing this forum: No registered users and 46 guests

Warm Glass

2575 Old Glory Road, Suite 700
Suite 700
Clemmons, NC 27012
Phone: (336) 712 8003
Email: wg@warmglass.com