My bowl didn't fully slump.

[Celene]

I made a 9" square bowl, with a 2" lip, making the bowl part a 5" square. I used 2 layers of System 96 clear glass that I had previously fused. I made a mold from 1" thick KL board, shaped like a frame so that the bowl would slump down to the kiln floor, however, it did not fully slump. I can see where the center of the bowl barely touched the kiln floor, so instead of a nice flat base, it's rounded. My question is, can I slump it again without slumping it too much? I have a Bonnie Glo fiber kiln and I used the pre-programmed schedule which is as follows:

200 F/hour to 1000F - hold 0 minutes
500 F/hour to 1280F - hold 20 minutes
Full (as fast as it can) to 950 F - hold 1 hour
100F/hour to 700 F with 0 hold then shuts off


Am I right in thinking I might need to increase the target temp. to about 1300F? Or do I need to hold it longer (maybe an hour) at 1280F?

Thanks! I hope I can get good at this because I'm really loving it!

[Brock]

Increase the time rather than the temp.
A right angle slump over a mild takes time.
LOOK!

[Laurie Spray]

The 500/hr is too fast. Learn your kiln by peeking and get rid of the preprogrammed schedules!
Take notes so you will know next time.

I would normally fire it
350/1200 0 hold
50/ 1250 hold 10. (Peek at 1250)
Anneal

Since this is a refire i would slow down to 250/1200
I think it will be fine refiring.

[Celene]

Thank you both for your advice! Laurie - How do you decide to slow it down 100 degrees? Do you just get a feel for it? Or is there a rule of thumb? I'm glad you both told me to peek...I keep reading conflicting information regarding opening the kiln. In my mind, it seems I would have to look in order to see what's happening, but everything I've read "scares" me into thinking I'll ruin my piece! At what temp. do you think it would be safe to look? And how often should I look after it hits that point? I suppose I just don't know how fast the glass slumps...

[Stephen Richard]

You can peek into the kiln any time after the softening point, if the only way of seeing in is by opening the lid. Peep or bung holes are really good features on any kiln.

[Laurie Spray]

Keep in mind..... Peeking is not fully opening the kiln. With good gloves on just open the kiln an inch or 2 until you can see what you need to see. Is the glass into the bottom of the mold?
No need to open it before 1200 as it more than likely will not be done and it always make you lose a few degrees which will slow the process down. Close the lip softly after peeking. Do not let it drop in a panic!

On other processes before i got to know my kiln well i would peek as long as the glass is above 1100 degrees.

When you glass comes out.....and is perfect of course.....start making a chart of your schedules.
Next time if you are using the same coe and thickness you will not have to peek! Shoot a few digitals.......take notes.......6 months from now after lots of experiments you will be glad you did!

[Celene]

Thanks for the advice everyone! My mold is dry and I'm going to re-fire today. With regard to Laurie's schedule - my schedule holds at the peak for 20 minutes, in addition to it being hotter, and yours only 10 - would that be because the ramp up is slower so it's actually slumping slower? Also, how long does it take for devitrificaction to occur?...If I end up having to hold it longer. Sorry - I know my questions might sound kinda dumb.

[Laurie Spray]

keep in mind it is time and temp.........the slower ramp makes your glass slump more evenly and you will not have to hold as long at the top.

[Mary Lou]

I made a 9" square bowl, with a 2" lip, making the bowl part a 5" square. I used 2 layers of System 96 clear glass that I had previously fused. I made a mold from 1" thick KL board, shaped like a frame so that the bowl would slump down to the kiln floor, however, it did not fully slump. I can see where the center of the bowl barely touched the kiln floor, so instead of a nice flat base, it's rounded. My question is, can I slump it again without slumping it too much? I have a Bonnie Glo fiber kiln and I used the pre-programmed schedule which is as follows:
!

Why are you slumping to the kiln floor? Do you not use a shelf? Unfortunately we've lost a few years of archived FAQ which would help you, but still, try searching first when you have questions and you might be surprised at how much info you'll find, not only on your current problem but one thread leads to another, and another and so on. Also, have you acquired any books, which would also give you more insight and info on the warm glass processes.

[Celene]

I'm sorry Mary Lou! I was actually reading on here for days before I joined and couldn't find what I was looking for. I guess I shouldn't be asking so many questions. I've been reading up on all of this since January. There is a lot to read. I also have several DVDs. Sometimes it's hard to put all the information together with so much and so many conflicting ideas. Today, though, I have started experimenting without following any "rules".

To answer your question, there is a benefit to having the Bonnie Glo fiber kiln - you don't need to use a shelf -you can fire directly on the floor - with shelf paper. It makes it possible to fire things more efficiently as most of the heat is absorbed into the glass as opposed to having to heat the shelf first.

[JestersBaubles]

If you do not have good air circulation around the glass, it will heat unevenly and you'll be more prone to breaks during the firing process. Perhaps the fiber construction allows this as they say, but I would be cautious if I had a lot invested into the piece.

Dana W.

[Celene]

Hmmmm....lots to think about! Thanks to all!

[Mary Lou]

Hi Celene, Didn't know that about the Bonnie Glo, but like Dana I've always thought you needed the air circulation around the glass??? When you use other solid bottom molds do you prop them off the floor?

Good that you've been doing some reading, believe me, you've only started. Have you read the BE Tech Notes? Very helpful even when working with 96 glass. I've found it helpful to invest in a few good books e.g. "Contemporary Fused Glass" by Brad Walker, "Fused Glass Art and Technique" by Richard La Londe, Boyce Lundstrom has several books, I have " Kiln Firing Glass" and "Glass Casting and Moldmaking", and then "The Joy of Coldworking" by Jonathon Schmuck. I have several others but the ones I mentioned are the ones I use for reference purposes. At the beginning you may find the reference books overwhelming but the more you work with warm glass the more sense they will make. Another hint, if you're not doing it, then keep a detailed log of each firing.

There is no need to apologize for asking questions on this board. That's one of its purposes. I find I get a lot of information from answers to questions from other members. Most times you will get the advice you are seeking, but you still have to apply it for your specific application. Also, read and learn as much as you can about heat work and how it applies to your kiln. Learn to understand schedules and if your kiln has a programmable controller, develop your own schedules and don't rely on the preprogrammed ones as Laurie suggested, throw them out. It is so important to know and understand your kiln. I was a little late arriving at this understanding but it makes a huge difference in the success of your work.

Good Luck and keep coming back. Mary Lou

[Celene]

Hi Mary Lou! The Bonnie Glo only has side elements...I don't know if that makes the difference??? I do not prop my molds up, but after you said that, I might try it out and see if there is any difference, good or bad.

I've kinda gotten the impression I've only just begun with the reading!...There is SO much information! I have not read the BE tech notes, but I will! Thank you! And thank you for the reading list! I don't have those ones, but I will definitely check into them! They sound like good ones to add to my collection! I have noticed that the more firing I do, the more the techinical information makes sense, but I think one of my main problems is that the Bonnie Glo seems to fire differently than I would expect based on what I've read. Everything I've read refers to brick kilns and in addition to that, there are top elements, side elements, etc... but there is no real explanation as to what difference it would make. I'm keeping logs, but I'm not sure I'm doing a good enough job...I have, however, noticed that with each firing they get MORE detailed!

Yesterday when I fired, I peeked for the first time, and it was very enlightening! That is the only way I see for one to learn what is actually happening! Without looking, how can you come up with solutions to a problem!? I agree about the pre-programmed schedules, but I think they are good to give a beginner a reference point. Now, after looking during a firing, I think I'll be coming up with my own schedules. I am one who has to learn by analogies, so today, I have been trying to compare melting glass with melting molasses. I want molasses to slowly soften and become fluid, but it can burn so easily, then when it cools, it stiffens up, but you don't want it to crystallize. Kinda like glass.

Anyway, thank you for the info! I'll check into those books for sure!
Celene

[Susanbuckler]

Hi Celene
I am too much of a newbie myself to offer suggestions about why your bowl did not slump but I want to let you know about these great bottomless molds for slumping. One of my problems with making deeper bowls was how to put a foot on it so it sits well without cold working machines like I used in classes. Laurie Spray, who has answered some of your questions, makes great bottomless molds to set on kiln fire paper or a kiln washed shelf. They fire beautifully and the bottoms are flat. Good luck!
Susan

[Celene]

Hi Susan! Thanks for the info! I was actually looking at all of Laurie's great stuff! I'm going to have to look more closely!

[Celene]

Mary Lou - I just finished reading the BE Tech Notes...VERY helpful! Thank you!

Celene

[Laurie Spray]

Hey you guys..... please never feel intimidated to ask questions..There are so many of you that are reading reading reading and you may be having some issue firing. Please ask! Everyone learns from it. So many of my customers say that they would "never" ask a question on this board. Somehow they got the feeling they were being a "bother". That is what the board is all about! Glass people helping other glass people.....So ask or email directly to someone who you think could help you! Use the search area but don't forget to ask.
Question Always with:
kiln type
firing schedule
glass set up
glass type....coe

come on......I can see you sitting there reading.......