Spilt glass

[frizzygirl]

Hiya

I tried a bullseye method of making a slab block but forgot to reinforce the walls. The glass spilled over and as you can see from the pic, the glass went onto the element, and the main body of glass has cracked.

Two questions. Can I use the kiln even though there is a small amount on glass on the side element, and can I used bits of the main glass or has it been compromised due to the crack.

Thank you in advance.
Tracey

[Stephen Richard]

Hiya

I tried a bullseye method of making a slab block but forgot to reinforce the walls. The glass spilled over and as you can see from the pic, the glass went onto the element, and the main body of glass has cracked.

Two questions. Can I use the kiln even though there is a small amount on glass on the side element,

Two possibilities I know of. Yes continue to fire as normal. Although the glass is quite corrosive to the elements, it will eventually drip off the elements. The other is to fire quickly to the 700C range and then switch kiln off and open the kiln to rapidly cool the glass. It will then fracture and is easy to pull off the elements without damaging them (in theory)

and can I used bits of the main glass or has it been compromised due to the crack.

If you mean to ask whether you can use bits of this glass in other projects, the answer is yes, although you may want to be careful as it would appear to be inadequately annealed

Thank you in advance.
Tracey

[David Jenkins]

How did the glass manage to jump the gap between the shelf and the elements?

[frizzygirl]

Hi Steve

Yes I lost the plot and just turned off the kiln in disgust. If I cut up the pieces and then anneal them properly, does that work or should I just bin it?


and Dave

I have no idea how the glass jumped across the gap as I had not touched it before the photo was taken.

[Kevin Midgley]

Thermal shock to the top piece pushed the wall away and sent it onto the elements.

You could try this at your own risk to remove the glass from the element.
Heat up to 200-300C. turn off and unplug/remove power to kiln. Open kiln with proper heat resistant and protective clothing.
Using a squirt water bottle set to jet spray, spray the glass stuck to the element and thermally shock it free.
Repeat cycle as necessary.
Element might break, or might not.
Practise squirting outside kiln. avoid hitting places other than the glass. Do it at your own risk.
I used a kiln for years after glass got stuck on the elements and wouldn't come off but they were Kanthal A1 not nichrome.
Cheaper kilns often have nichrome elements.

[frizzygirl]

Hi Kevin

Sorry to be thick but this is the first time I have tried a piece of glass thicker than 6mm.

So I am not put off trying again, why would thermal shock have caused the glass to break and throw it over to the elements when I had not opened the kiln until it reached it full fuse time. I only opened it when I had to drop the temp quickly to the next phase suggested by bullseye. When I opened it the glass was all over the placed, and so I turned the kiln off.

Many thanks
Tracey

[Stephen Richard]

You haven't shared with us the firing schedule, but as the glass was broken and rounded, the thermal shock occurred on the way up in temperature. So your rate of advance was too fast in the glass' brittle temperature range. At least this is my assumption.
For confirmation or otherwise, you need to give us as much information as possible on the firing conditions.
I also am not sure whether you (or I) have understood Bullseye's recommendation correctly. I see no reason for shock cooling of the slab from top temperature.

[Stephen Richard]

I for got.
Also, since you simply turned the kiln off from the top temperature, the glass has not had the opportunity to anneal. That is a reason for a crack in the glass now - which would have occurred on the way down in temperature.

[Mike Griffin]

Hi Steve

Yes I lost the plot and just turned off the kiln in disgust. If I cut up the pieces and then anneal them properly, does that work or should I just bin it?


and Dave

I have no idea how the glass jumped across the gap as I had not touched it before the photo was taken.

The kiln shelf looks to be very close to the side wall where the glass touches the elements. The flowing molten glass will tend to assume a thickness of 1/4 of an inch so if the gap is anything like that, even a little wider then the glass will get on the elements.

[Mike Griffin]

As well, try to remove as much glass as you can from the fire brick or it will progressively eat it's way into the brickwork.

[frizzygirl]

Hiya

Thank you for all the replies and help. I will do as instructed - probably not brave enough to do the water squirt bit tho, so will see how much is left after the next full fuse.

Just putting on the fusing program - although now I think about I don't know if it was cracked when I opened it as I was so disappointed that the thing had overflowed so maybe it happened on the way down?

The bullseye schedule for the pattern bars is

C F C F
148 (300) 663 (1225) 45mins
315(600) 829(1525) 1hr 30mins
AFAP 482(900) 3 hours
7 (45) 426(800) 1 min
27(81) 371(700) 1 min
AFAP 70

I presumed afap was opening the kiln lid, making my jeans smell of burning cotton until it reached nearly 482 C.

It may be awhile until I try this one again.

Many thanks
Tracey

[Kevin Midgley]

get rid of the glass on the elements NOW.
Suggested method could be used.
If not removed now, it will only become worse with time and do more damage to your kiln.
Turn it off.

[Valerie Adams]

I think your biggest problem was not setting up your dams correctly. Pinwheel the shelf sections around the glass, then support them with more kiln furniture. The glass became liquid and pushed them out, allowing the glass to flow off your shelf and into your elements. Without knowing what your lay up was, I can't tell if the white area in the center is glass or a void showing fiber material. I don't think thermal shock was your problem, I think it was inadequate damming.

As for your elements, unplug your kiln and use a Dremel tool to grind off the offending glass. Three years ago I had a huge kiln meltdown where my lid's elements fell out and into molten glass. I Dremeled off the glass, tucked the elements back in, and use it several times a week.

[Morganica]

I think David's question is an interesting one, and makes me think there may be something else going on here, too. There looks to me more than a half-inch of space between the edge of that kilnshelf and the side of the kiln, and your elements are well above the "fill line" for the spilling glass. Glass that's overflowing from a dam doesn't have all THAT much momentum and is moving fairly slowly. I'd expect it to flow across the shelf and straight down to the kiln floor. So how did the glass get onto the element in the first place?

Two possibilities I can imagine:
--The glass thermal-shocked and exploded across the kiln. I think this is most likely, especially if you had any prefired/failed pieces in your pattern bar mix. If that glass thermal-shocked, it could do it with enough force to both move the dam and send a chunk of glass across to the element. I've had pieces thermal-shock badly enough to displace a heavy ceramic mold a couple of inches...

--You had a really soft glass, such as black, next to a really hard glass, such as white. The soft glass would become runny and push the dam out, and carry the harder glass on its "back." When it hit the edge, the soft glass would go down, the hard glass would move forward and lodge into the element. Doesn't seem very likely, especially since it looks like there's light glass on the shelf and dark glass on the elements, but hey.

Interesting speculation, anyway.

[Mark Wright]

The glass gods are not happy right now. Last night I had a similar failure and I am not sure why.
I was more fortunate than Tracey in that the kiln and the kiln shelf survived even though half of it moved about 2 inches and melted over the edge of the shelf.
The piece is a wire melt and this was my 5th firing to do crater repair, sandblasting, flip and fire, etc. Same schedule used all 5 times.

400 to 1100 hold 10
200 to 1240 hold 30
400 to 1480 hold 30
AFAP to 900 hold 45
150 to 750 off

The original wire melt was done at 1550 with a 30 minute hold.

Never happened to me before. The glass is all Bullseye #114 & #1114 Blue, #113 White, #421 Pink, #141 Green and lots of clear.

Any thoughts are appreciated.
Mark

[Warren Weiss]

Thermal shock on the way up. Try 200 dph to 1100 then 400 to 1480. No benefit of 30 min hold at 1240.
Warren

[Morganica]

With these types of breaks it's useful to not only look at the firing schedule where the break occurred, but also to look at the schedule for the previous firing. Frequently the glass is coming off the last cycle with insufficient annealing, so thermal shock is far more likely.

Mark, you're on your fifth firing with a high-temp piece, so I think that's what probably happened here--too aggressive on the previous anneal, too fast on the ramp up. With that much firing/coldwork/firing there's also a chance that one or more of the glasses might have shifted compatibility a tad. If it's not too bad, slowing down the anneal would also prevent it from cracking out of the piece.

I'd agree with Warren that you can dump the bubble squeeze--that's for slowly softening the glass, pushing out excess air between pieces to prevent bubble formation. If you're adding frit to holes it might be of some use, but otherwise, you've got a solid piece of glass so the squeeze isn't doing anything.

[Kevin Midgley]

try annealing the glass.
Might help to read Graham Stone's book a few times cover to cover to figure out a real, proper schedule.
Apologies for being blunt.

[Stephen Richard]

AFAP meas as fast as the kiln will cool without assistance such as opening the kiln. Most will cool to the annealing temperature in an hour or so and that is fast enough. The recommendation to read Stone's book is a good one though.