Bubble or "Tumor" Forming During Slump

[glaswizz]

Good Morning All,

I am having an issue that I just cannot seem to correct. I've tried every variation I can think of, and nothing seems to be working. Here's the issue. I am taking a fully fused "blank" (Spectrum black with clear cap, fully fused, no problems) and putting it in your average 10" plate mold. Seems simple. Apparently not.

I ran it yesterday only to go out and find a giant "tumor", or whatever you want to call it, had formed on one side. No big deal, but this has now happened at least 4 times. I have tried every variation I can think of. The first time had a design element on it, so I thought that caused it. Took that out, still happened. Tried ramping up at different speeds thinking maybe I was going too fast, too slow. Still occurring. I am at my wits end. Now I don't know if there is something wrong with the mold or the kiln or if I am still just doing something obviously wrong. It wouldn't be so troubling if I hadn't run this same style of plate using the same mold a ton of times with no problems.

Here's all of the info I think you will need. I have a Jen Ken 15-6, coils on top and sides.
I am using Spectrum clear full fused over solid black.
I have put the 10 plate mold onto small kiln posts to make sure it has air circulation and that the hole in the bottom is completely clear.
My schedule this final time was...
400-1100-0
200-1250-20
AFAP-960-45
100-700-OFF
I have adjusted the second ramp (the 200) from AFAP to 800dph to 500dph to 200dph. For the most part the rest of the schedule has remained the same. I just don't know what to do any more. I've done other project in between these mishaps and everything else seems to be firing ok, as long as I'm not using this mold. I have checked out the mold and can't find anything that jumps out at me as causing the problem. I think the first time it happened I may have just primed it, but I haven't since. Any suggestions would be EXTREMELY appreciated, as I am about to lose my mind.

[vblue]

You said you are using a plate mold. Are there holes in the bottom of the mold? Are they plugged with kilnwash preventing air from being pushed out? Did you raise the mold on kiln posts so the air will definitely be pushed out?

I think your schedule is too fast. I seldom do anything but 200 dph to slumping temperature...etc.

Vernelle

[glaswizz]

Thanks Vernelle.

I have put the 10 plate mold onto small kiln posts to make sure it has air circulation and that the hole in the bottom is completely clear.

[KarunaS]

Do you have a picture of the mold/piece? You may need more than one hole in the bottom of the mold.

[glaswizz]

I don't have a pic of the slump handy. I can post it later. The mold is this one...

http://www.delphiglass.com/glass-molds/ ... nner-plate

It has a single hole in the bottom. My first thought would normallybe the hole, but why would it have worked for the last 4 years or so and now start having problems?

[CH Glass]

I have a mold similar to that. Mine has four holes equally spaced around the inner circle, and no hole in the center.

[KarunaS]

I don't have a pic of the slump handy. I can post it later. The mold is this one...

http://www.delphiglass.com/glass-molds/ ... nner-plate

It has a single hole in the bottom. My first thought would normallybe the hole, but why would it have worked for the last 4 years or so and now start having problems?

It's easy enough to drill additional holes in the mold and see if that solves the problem and it takes one potential issue out of the equation. I had the same problem with one of my molds a couple of years ago which worked fine many times and then surprised me with a bubble...this one had holes around the perimeter and got a bubble in the middle; no problem since making a middle hole.

[glaswizz]

Thanks. I've never drilled a hole in a ceramic mold before. Do I need a special bit? Does it have to be wet or anything like glass does?

[KarunaS]

Thanks. I've never drilled a hole in a ceramic mold before. Do I need a special bit? Does it have to be wet or anything like glass does?

I just used my Dremel with an old diamond bit; I think any small drill bit would do. No need for water.

[rosanna gusler]

masonary bits work better than wood bits in fired clay. rosanna

[Jeanne]

I've used a 1.5 mm diamond bit. Works fine.

[glaswizz]

Thanks, I'll try that.