WarmGlass.com

Had an issue with slumping a bowl made from Spectrum 96 glass. We always use B.E but had some of this still around and wanted to try slumping a larger bowl. Have been fusing for just over one year.

Slumping Program used is as follows fired in EvenHeat Studio 24 Kiln
400F 1265F :20min
AFAP 900 1:00hr
150 700 :00

The glass is 6mm thick and consists of a dark grey and one of Spectrums speciality glasses. There were no numbers on the glass and purchased from the only store in Fairbanks that sells fusible glass.

It was cut into an 11" circle and fired. The black spiral glass was fired on top and had no issues. The gray that was in contact with the thin fire had some spots that looked to have trapped some of the paper. I sandblasted it with AO-120 and washed with soap and water then alcohol before slumping. There doesn't seem to be an issue with the grey finish after the slump.

The piece was then put into B.E Classic mold #8723. It was centered perfectly and then fired to above schedule. The bottom picture shows it somewhat, but the bowl is out of round by a good 3/8". I am assuming that the glass shifted while it was firing. I have since read on this site (suggested by Brock) that it helps to put a small bevel on the glass that is in contact with the mold to prevent slippage. I will do this from now on.

The other picture hopefully shows well enough the other issue with slump. The glass looks to have small stretch mark and a hazing (devit ?) on the surface that came into contact with the mold. I am not sure if the stretch marks were caused by slumping too fast? As for the hazing, I am not sure what the cause of that is.

Have done a lot of fusing and little slumping as I am still in the early stages of learning. This site has been a wealth of info and many hours have been spent just reading posts on issues people have. Any input would be greatly appreciated and let me know if further info is needed.

Cheers

My slumping schedule is more conservative. I've had issues with uneven slumping and slowed way down. I'll ramp @ 300 per to 1100 and hold for 20 min to ensure an even soak then ramp to 1250 @ 50 per. No issues to date. Also, make sure your kiln and shelf are as level as can be.

The bevel that Brock suggested was to enable the glass to slide on the mold rather than get hung up and cause the glass to de-center itself.
As for the glass, use Bullseye
More seriously some glass will because of its formulation to create the colour being used, will have a 'personal interest' in devitrifying. They are the glasses that want to stick to the kiln wash or whatever else they are sitting on in the kiln. Rarely clears but always opaque glasses.

Thanks for the replies. I will adjust the schedule to slow it down some. I am always checking the shelf for being level.

As for the glass, BE is what we solely use. Just wanted to experiment with the few pieces of 96 we had. Never understood why the 96 glass is smooth and almost like window glass on both sides. Each piece of BE glass seems to be a work of art in itself.

Was going to attempt flattening this piece and trying again. Need to research some more to come up with a schedule to do just that.

Appreciate the input.

200 dph to 1200, hold until slumped (look at it), then drop to 900 etc. No need for elaborate holds at 1100 etc.
Each mold will fill at a different time/temp.
Trying to flatten that piece will not give you joy. I'd give it away and start on the next one.

Marty wrote:No need for elaborate holds at 1100 etc.

I would hardly call a 20 min hold at 1100 elaborate.

Harmless hyperbole. I was thinking of some of the meaningless schedules posted here, like the 10 minute hold at 350, then a change in ramp to 500 with another small hold, and so on. Why hold (and why there) at all for a simple slump? What's going to happen?
If it's faith-based, that's a valid reason....

Marty wrote:Why hold (and why there) at all for a simple slump? What's going to happen?

My previous "go to" schedule was not far from yours, although I ramped at 300 per. As mentioned, I had issues with certain molds slumping unevenly. Maybe the design of the mold. Who knows, who cares. Frustrating to lose a piece on the final step. And as you said, you cannot really salvage the piece after that. I figure that at 1100, the glass is just about ready to move. A hold at that point ensures the glass is evenly heated throughout and a slow transition up to my final temp allows the center of the glass to soften and fall, as it is unsupported, before the edges get hot enough to soften and slip causing an uneven slump. I have 6 programs set up on my controller. Five are set, one is static. I will change the final temp and hold on my programs to achieve best results. If you do the math, my program time is less than an hour longer than yours. That's negligible in "kiln time". It's worked for me flawlessly for years and since it's the mantra of the majority of this board here that slower is better, my question is why not.

Since we are still in the infancy stages of learning I have no issues with giving it a go and trying to slump it flat. The time may (will) come where I have to try this on something more important and it doesn't hurt to learn all we can before then. Nothing to lose except a little electricity and maybe some glass.

The input from everyone is much appreciated. Will post a reply after the attempt. It's my wife's bowl anyways, so what could possibly go wrong, right?

This forum has been very helpful in the learning process.

Wrangell wrote: Slumping Program used is as follows fired in EvenHeat Studio 24 Kiln
400F 1265F :20min
AFAP 900 1:00hr
150 700 :00

... then put into B.E Classic mold #8723. It was centered perfectly and then fired to above schedule.

Bullseye's recommended schedule for that mold is 300dph to 1225 hold 45 minutes. 1265 is probably too high, especially with Spectrum glass. That can cause the problems you experienced.

Like Marty, I would prefer the hold at around 1200 for however long it takes. You only have to watch once, keep notes and you won't need to watch again.

You'll probably find it quicker and more satisfying to just make another one rather than try to flatten and refire.

By the way, not all of us are "in the infancy stages of learning." Some have progressed to adolescence.

JamesL wrote: I figure that at 1100, the glass is just about ready to move. A hold at that point ensures the glass is evenly heated throughout and a slow transition up to my final temp allows the center of the glass to soften and fall, as it is unsupported, before the edges get hot enough to soften and slip causing an uneven slump.

I do a lot of drop ring vases and I actually play this the opposite direction: Fast " transition up to my final temp allows the center of the glass to soften and fall, as it is unsupported, before the edges get hot enough to soften and slip causing an uneven slump." Like, I've been doing some 2" circles as drops over a 1/2" hole (repurposed kiln post ). Now, a 3mm piece will take "forever" to slump over a hole that size since the glass doesn't weigh enough to get moving, so I "cheat" before the edges get soft and push in/down the center with a single point raking tool. A beautiful way to make a Morning Glory or other smaller trumpet flower.

But yeah, rarely taking a slump or drop in COE 90 over 1260-1270. Have a few really shallow bowls and plates I take to 1280, 20 hold, no watching. They ain't going anywhere with only an inch or so to fall.

Marty wrote:Trying to flatten that piece will not give you joy. I'd give it away and start on the next one.

[Strictly rhetoric] Unless you were making a sea-shell styled bowl. Then you might get away with it or actually improve it's look. Hey, it worked the one time.

Wrangell wrote: The bottom picture shows it somewhat, but the bowl is out of round by a good 3/8". I am assuming that the glass shifted while it was firing. I have since read on this site (suggested by Brock) that it helps to put a small bevel on the glass that is in contact with the mold to prevent slippage. I will do this from now on.

Having a raking tool(just the simple L-shaped stainless steel poker is fine)you are frequently able to gently poke and pull a piece back onto center between 1000-1250-ish.
Brock's suggestion is the good one.

You state that there was no number code on the glass. I do not recognize this as a "96" color... Because there is so much Spectrum out there that is not tested fusable I would suggest this glass is not "96".

Did a little more investigation on the glass. As long as my wife doesn't read this, I'm good. Otherwise

Since this was one of her projects and not mine, she said there was not a number on the glass. Come to find out the 96 did have a number (OA/3005-95F Opal Art) Have been telling her to keep really good notes on each project but that's a bad subject.

All the glass that I use is B.E and now pretty much the same for her. As mentioned before, we have very little 96 and trying to use it all up. So to address Don's comment, it is fusible 96 glass. We even went to the store where we purchased it and confirmed this.

Been working on learning the Leatherbarrow crackle and pebble techniques (thats a whole other Topic) so haven't flattened the bowl yet.

One other question. Would it be a good idea to sandblast the devit piece before slumping or just see what happens? Was planning on sandblasting it as it only take a couple of minutes to do so.

Sandblast it.

Wrangell wrote:Did a little more investigation on the glass. As long as my wife doesn't read this, I'm good. Otherwise

Since this was one of her projects and not mine, she said there was not a number on the glass. Come to find out the 96 did have a number (OA/3005-95F Opal Art) Have been telling her to keep really good notes on each project but that's a bad subject.

All the glass that I use is B.E and now pretty much the same for her.

You two need this thread - stat. http://www.warmglass.com/phpBB3/viewtop ... 41#p361441\

But seriously, you might want to consider getting rid of ALL your 96 glass if you fear this will be a repeat problem - there are always ebayers looking to buy small, odd lots. I bought a used kiln about 5-6 months ago that came with easily $500-600 of COE 96 frit and sheet glass, and we are strictly 90. Sold it all to avoid this issue . . . Ditto with our old stained glass stock - people making mosaics love buying a 5-10 lb box of chips for $5-8/lb.

It's great you have a sandblaster - what Brad said.

Edpal247, appreciate the link to the post. It had me laughing and is about spot on to my situation.

Was reading another of your posts after reading this one and noticed you mentioning that you're "now the R&D department". Damn near spit beer on the computer on that one as it hits home perfectly here. I'm a metal worker and do art pieces with copper, steel and other materials. My wife had dabbled with stain glass for years and then gave it up. She decided she wanted a kiln so we got one. Next thing you know, I'm hooked on it and next thing you know, the process of R&D starts but it's a one way street as I'm sure you are all too familiar with. I don't mind the R&D end, it's just then having to interpret it into something she understands.

Trying to get confident enough to start incorporating it in with some of my metal pieces. Can tell you that we don't regret getting fused glass art though (89% of the time anyhow