WarmGlass.com

hey guys ,would anyone care to tell me what is going on with my bowls, this is the 3rd time i have tried to slump one, and always the same result. they only slump on one side. this blank, i cut and fused a bit more over sized (1/2 an inch) for the mould,, hoping that i would get a better slumping . don't worry about the lumps on the bottom i added some glass sealer to make a flat bottom..the kiln is a very old one with out top elements. all the elements are working, but i am wondering if it the kiln has a "cold side" to it . i looked in as the temperature was at 700 dec celsius after about 5 minutes but it hadn't slumped so held it at 700 for a few more minutes and opps any held would be much appreciated

Every kiln fires differently and cold spots are definitely a possibility. Bullseye has a tip sheet on doing a kiln test to check how your kiln fires. I recommend it.

Can you show us a picture of the original mold? How big is the kiln, where are the elements and how are you placing your molds in relation to the elements? Is that a streaky glass you're trying to slump and/or are there a bunch of colors, especially high-contrast colors, in this piece? is the kiln fusing at expected temperatures?

Without seeing the actual slumping mold it's hard to say, and you certainly could have something going on with one side of the kiln--running some "Know your kiln" tests would help. If I saw this in my own studio, though, I'd probably think it was an incomplete slump. Some things take 5 minutes to slump, some take 2-3 hours, depends on the mold, the depth and angle(s) of the slump, the type of glass, the schedule you used getting up to process temps...lotsa things. Slumps may or may not slide down the mold evenly, especially with faster schedules, although if you let them continue and monitor closely, they'll usually wind up where you want them.

Or it could be as simple as the glass not quite fully centered on the mold. Hard to tell without more information...

Too much overhang. Your perimeter elements are heating the overhanging edge before they heat the interior of the disc. Others were looking for a cold spot. I would also look for a hot spot. If the over hanging glass bends downward before it falls in, it can easily create the hangup you show.

A very simple trick to ensure success when slumping into bowl forms, is to start inside the mold. Place your blank down from the rim a little bit and that places the blank under compression helping it to slump evenly.

Is the shelf and mold level?

It also appears that the mold is not symmetrical. The right side looks steeper than the left and thus slumped deeper.

Did the glass "bottom out" or was the slump stopped before it had completely formed to the mold?

Jim

Brock:

Brock wrote:A very simple trick to ensure success when slumping into bowl forms, is to start inside the mold. Place your blank down from the rim a little bit and that places the blank under compression helping it to slump evenly.

I have a question....do you mean that the glass should be smaller than the bowl to start with? So if the mold is a 9" circle, then we should start with a 8 3/4 inch glass to slump? Just trying to understand

Rachel
imaglassydiva@aol.com

I always start with
a form that is 1/4" over the edge. I think it is all about slowing down after 1150 or so.......

WOW i didn't expect some many replys ,,,i thank you all.. yes the mould is a deep one 7 3/4 " wide and 4" deep,,yes i have been working on easy things till now.and buying moulds and such is very difficult in Christchurch NZ (earthquake closed most of our shops)..the kiln is a very old one, only manual settings 15"x15"X18" deep, i know this is most of the problem,will be looking at getting a new one later in the year..the glass is 2 layer of fused urobros glass..the first 2 bowls i tried the blanks were in side the mould and got the same uneven slumping that is why i make this blank a bit bigger, was hoping to get a bit of a hang back on the top as the middle started to slump in to the mould.. i shall try some of the heat tests too see just how uneven the temp is in the kiln...after having worked with cold glass for 20 odd years i find this warm glass a real challenge...having created some near impossible works in glass in the pass... but never let it be said ,,that i wont rise to a challenge lol
again many thanks guys

RachelM wrote:Brock:

Brock wrote:A very simple trick to ensure success when slumping into bowl forms, is to start inside the mold. Place your blank down from the rim a little bit and that places the blank under compression helping it to slump evenly.

I have a question....do you mean that the glass should be smaller than the bowl to start with? So if the mold is a 9" circle, then we should start with a 8 3/4 inch glass to slump? Just trying to understand

Rachel
imaglassydiva@aol.com

Exactly. Get a big wok and you have a mold for any size. Level the mold, level the glass, (you don't have to level the floor or the kiln or the shelf) and you can make bowls of any size smaller than the wok.

RachelM wrote:Brock:

Brock wrote:A very simple trick to ensure success when slumping into bowl forms, is to start inside the mold. Place your blank down from the rim a little bit and that places the blank under compression helping it to slump evenly.

I have a question....do you mean that the glass should be smaller than the bowl to start with? So if the mold is a 9" circle, then we should start with a 8 3/4 inch glass to slump? Just trying to understand

Rachel
imaglassydiva@aol.com

Exactly. Get a big wok and you have a mold for any size. Level the mold, level the glass, (you don't have to level the floor or the kiln or the shelf) and you can make bowls of any size smaller than the wok.

BUT, I scrolled down and saw your mold. That is WAY too steep for a one slump bowl. Find some molds with gentler sides. Hmmm, woks work great.

For SS forms you can slump INTO the mold? Say I have a deeper mold like he does, can I slump it in a different mold first to start the slump and then switch to the deeper mold? Should the first slump be in a smaller mold..or bigger? To start the slump.
I've wondered about this as I have deeper SS bowls I'd like to use

Thank you!
Sheree

you can but sometimes the glass gets stuck on cool down. i use a really soft and thick layer of kiln wash over the top of my regular mold wash to help with this issue. r.

Karl Harron is the hottest teacher out there these days. He did a lot of research and development to create a set of molds designed to get to a deep slump. You start out with a precise circle and mold, and each step brings you to a new, perfectly sized, deeper mold.

Karl is teaching at Oatka Glass in Batavia, NY this spring and summer. Great studio.
I've taken beginning & internediate fusing clases with owners, Lance & Amanda Taylor. B & B to stay nearby.
Studio is about hour and half from Cornning.