bullseyeglass.com • View topic - Slumping problem: Glass got hung up in mold

Slumping problem: Glass got hung up in mold

For discussion of processes related to using Bullseye glass, including kilnforming and kilncasting, torchwork, blowing and stained glass.

Slumping problem: Glass got hung up in mold

Postby jtensminger » Tue Oct 03, 2017 4:15 am

I made an 8" square plate, using on-edge construction; thickness is 3/8" and even throughout.
I slumped it in Bullseye classic 12-1/2 " round mold (#8723). I've done this often, successfully, and like the "squared bowl-ish look.

The mold had a fresh application of kiln wash---not my neatest job but it felt smooth. The edges were sanded smoothly, with a slight bevel, using wet belt sander. To compensate for steep slump and thickness, my slumping program was :
Segment 1 - 300, 1225F, :45
Segment 2 - AFAP, 900F, 1:30
Segment 3 - 100, 700F, :00
Segment 4 - AFAP, 70F, :00

The dish slumped unevenly. Two adjacent edges are ragged--obviously got hung up on the mold. What do you think happened? Should I try to re-slump in the same mold or use a different mold like the BE Deep Form Step 2.

Trying to upload picture as attachment but don't think it's working.
jtensminger
 
Posts: 15
Joined: Thu Jan 24, 2013 7:23 am

Re: Slumping problem: Glass got hung up in mold

Postby marykaynitchie » Wed Oct 04, 2017 9:04 am

Hi,

A photo would be helpful! If you cannot upload one, send one to me via email.

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
marykaynitchie
 
Posts: 1195
Joined: Thu Oct 13, 2011 5:39 am

Re: Slumping problem: Glass got hung up in mold

Postby jestersbaubles » Wed Oct 04, 2017 6:56 pm

For slumps, I have good success with ramping to 1100, holding for at least 30 minutes, and then ramping on up to my target temp. With the hold at 1100, the glass will gently start to settle in the mold and most likely start to sag a little.

Dana W.
Dana Worley Fused Glass Designs
dba Jester's Baubles
http://www.jestersbaubles.com
http://www.jestersbaubles.blogspot.com
jestersbaubles
 
Posts: 233
Joined: Thu Jan 21, 2010 6:29 pm
Location: Logan, UT

Re: Slumping problem: Glass got hung up in mold

Postby jtensminger » Thu Oct 05, 2017 12:52 pm

Hi. I figured out how to attached photos and am reposting my original query. I sent you an email but not sure it reached you.
So....I made an 8" square plate, using on-edge construction; thickness is 3/8" and very even throughout. I slumped it in Bullseye classic 12-1/2 " round mold (#8723). I've done this often, successfully, and like the "squared bowl-ish look. The mold had a fresh application of kiln wash---not my neatest job but it felt smooth enough. I did forget to raise the mold on a kiln post. The edges were sanded smoothly, with a slight bevel, using a wet belt sander. To compensate for steep slump and thickness, my slumping program was :
Segment 1 - 300, 1225F, :45
Segment 2 - AFAP, 900F, 1:30
Segment 3 - 100, 700F, :00
Segment 4 - AFAP, 70F, :00

Two issues: (1) The slump is unevenly distributed, e.g., the bottom is off-centered. (2) Two adjacent edges are ragged/splintery--it looked like one side became stuck. Why did this happen? More importantly, how can I fix it? I was thinking of re-slumping in a different mold like the BE Deep Form Step 2 which could result in an interesting shape. Thanks for your attention.
Attachments
slump pblm top view.JPG
Top view of dish. Uneven, edge has curled inward.
slump pblm top view.JPG (31.75 KiB) Viewed 20798 times
slump pblm edge .JPG
Adjacent edges are full of needles. It was perfectly smooth before slumping.
slump pblm edge .JPG (23.54 KiB) Viewed 20798 times
jtensminger
 
Posts: 15
Joined: Thu Jan 24, 2013 7:23 am

Re: Slumping problem: Glass got hung up in mold

Postby marykaynitchie » Mon Oct 09, 2017 4:28 pm

Thank you for your patience while we worked on a reply.

Here is advice from one of our instructors and project designers, Bonnie:

It appears that the piece was flipped and slumped with the shelf side facing up/glossy side against the mold. The glossy side, which has no trace of separator, can become tacky at slumping temperatures and is more prone to get hung up than the original shelf side would. The issues mentioned (off center & jagged edge) both stem from the glossy surface becoming sticky and getting hung up on the form. When flipping a piece for slumping, selecting a mold that requires little heatwork with a gentle curve will be more predictable and is less likely to get hung up. When you’ve combined a square w/ the 12” Classic & have had success –was it with the shelf side against the mold?

You could try a Deep Form slump at this point, but the issues are the same. I would smooth & re-bevel the edges before the 2nd slump.

You could also try flattening the piece by firing on a primed shelf (with the open side of the bowl face-up). For this shape, I’d run the same cycle as you’ve written & plan to be around to observe during the process soak to adjust as needed. I’ve been surprised by this before & have rescued a piece or two this way. It’s not a sure thing, especially as the piece has stretched a bit, but may be enough to take it to the next step, whatever that may be. The glossy side will continue to take on slight impressions of whatever it is fired on. I wouldn’t fire hotter than a slump to maintain the crisp design, the surface of which will also reflect the heat work of multiple firings.


We hope this helps you plan your next steps!

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
marykaynitchie
 
Posts: 1195
Joined: Thu Oct 13, 2011 5:39 am

Re: Slumping problem: Glass got hung up in mold

Postby jtensminger » Tue Oct 10, 2017 10:52 am

Thank you Bonnie. Excellent post-mortem analysis--- I would never have figured it out myself.

Yup, I did flip it and slump with the glossy side down. I have a feeling that my prior successes were slumped in a gentler, ball surface mold I would like to try flattening but do not understand what kiln program I should use. Could you provide one? The piece is 3/8" thick, on-edge strip construction.
jtensminger
 
Posts: 15
Joined: Thu Jan 24, 2013 7:23 am

Re: Slumping problem: Glass got hung up in mold

Postby marykaynitchie » Wed Oct 11, 2017 10:07 am

If you know your mold style number, you can look up a suggested cycle here, that we found worked in our studio:

http://www.bullseyeglass.com/methods-id ... dules.html

Remember that your cycle may vary depending on your individual kiln, so this is a starting point.

Hope that helps!

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
marykaynitchie
 
Posts: 1195
Joined: Thu Oct 13, 2011 5:39 am

Re: Slumping problem: Glass got hung up in mold

Postby jtensminger » Fri Oct 13, 2017 4:26 am

Your advice worked out beautifully. I re-fired the bowl using my original slumping schedule but reduced the Process hold time to 20 minutes. It is flat and retained the 8" square footprint and thickness. I never tried to flatten a piece before and my instinct would have been to full-fuse it. Thanks so much.
jtensminger
 
Posts: 15
Joined: Thu Jan 24, 2013 7:23 am

Re: Slumping problem: Glass got hung up in mold

Postby marykaynitchie » Fri Oct 13, 2017 9:55 am

Thank you for reporting on what worked for you!

Mary Kay
Mary Kay Nitchie
Bullseye Glass Co.

Subscribe to Bullseye kiln-glass videos at
bit.ly/BullVideos
marykaynitchie
 
Posts: 1195
Joined: Thu Oct 13, 2011 5:39 am


Return to Technique

Who is online

Users browsing this forum: maja.cl and 1 guest