Glass moved during slump

[Susanbuckler]

Hi (again....am I asking too many questions?)
Can anyone tell me why a piece of glass moves off the center of the mold during slumping?
See photo below
There were 4 squares in the kiln
Two 3x 3
Two 4 x 4
The smaller ones both moved off center
The larger ones remained fully on the molds
Thank you
Susan

[lorimendenhall]

I have no idea but how frustrating!!!

[Marty]

Heat differential?
Not perfectly balanced on the mold?
Overhanging the mold?
Glass heavier on one side?
Wonky mold?

try: more careful placement, slower ramp up, putting a slight bevel on the bottom edge so it sits in the mold better.

[David Jenkins]

Did it actually move to that position during the slump? Or perhaps after? I guess I'd want to know: Did the overhanging edge that's now off the mold slump so that it's hanging down? It's hard for me to tell, but it doesn't look like it did.

[Bert Weiss]

expansion plus gravity

[Marty]

expansion?

I just noticed that the one in the lower right corner is off the mold too.
Did the kiln get jostled during the firing? Then why are the other 2 ok?
I'd also like to see a photo of that stringer piece outside the kiln- it's hard to tell if it slumped wonky or if it's just displaced.
Could this be a set-up?

[Bert Weiss]

expansion?

I just noticed that the one in the lower right corner is off the mold too.
Did the kiln get jostled during the firing? Then why are the other 2 ok?
I'd also like to see a photo of that stringer piece outside the kiln- it's hard to tell if it slumped wonky or if it's just displaced.
Could this be a set-up?

Expansion creates some movement.

[Marty]

Maybe with a ss mold, not with ceramic at slumping temps. How much does the glass expand/contract at 1200F?

[Bert Weiss]

Maybe with a ss mold, not with ceramic at slumping temps. How much does the glass expand/contract at 1200F?

My thought was simply that the heat makes both mold and glass expand at different rates. This could be just enough for the center of gravity to shift enough to make the glass move. We know that nobody reached in and moved it. We also know it moved. It could be that the dog bumped in to the kiln...

[David Jenkins]

I'm interested in the area highlighted in this screenshot: Did it fall over/slump over the edge of the mold? Or has the piece slumped ok, but it has just been moved/offset in the mold at some point after the actual slump was completed?

2013-04-16_1735 small.png (114.5 KiB) Viewed 18307 times

[Laurie Spray]

I was wondering that too David..... Looks like it was jarred after done slumping. The edge looks as if slumped perfectly and is not bent over the edge. Susan?

[Susanbuckler]

wow...thanks to all who answered.
here we go...most importantly, I doubt the dog kicked the kiln.
now that we've gotten that out of the way....

Marty..my kiln seems to heat evenly and the prior fuse with the tiles prepared at the same time and slumped a few days before using the same molds slumped perfectly. I believe the tiles were well balanced on the molds and were not overhanging. glass was evenly distributed & molds are in good condition.

David...i do not know exactly when it moved because I did not open the kiln until it cooled down. it was in that position when I gently opened the kiln. but i think it happened during the slump and not during the cooling

Bert...not sure what you mean "expansion plus gravity".....this is a newbie forum. if expansion plus gravity results in something like this, why have I not seen it before? I've used these little square molds many times to slump test tiles. Maybe....because these are so small, it is easier for expansion to cause them to move?

Marty...yes, both 3 X 3s slightly popped off their mold. no jostling to the kiln. it's in the garage, away from the activity.

David...the section you outlined in orange...the area slumped over the shape of the mold, off center. it must have happened sometime during the slump, before the cooling.

Laurie...piece is not slumped perfectly., to use Marty's term, it's a wonky slump. and yes, both 3 X 3s moved off the mold.

i took a picture of both pieces but I cannot get the angle right to show it to you more clearly.

thanks for all the dialog. I will be sure to check the placement of the blank on the mold very carefully.

[Marty]

Susan- that's a puzzle (I admit to thinking you were playing Stump the Chumps!).
I'd do exactly the same thing again and if you still got movement, then try the bevel trick- it'll seat the glass into the mold a little better.

[Kevin Midgley]

It may seem weird but:
Earthquakes do happen.
Was it close enough?

2.8 13km N of Brownsburg-Chatham, Canada 2013-04-15 13:32:27 45.803°N 74.447°W 10.0

http://earthquake.usgs.gov/earthquakes/map/

[Susanbuckler]

Not likely..I live in the mid Hudson valley of NY

[David Jenkins]

Do the small molds have airholes in them? Do the large ones have airholes? It doesn't look like your molds were set up on kiln furniture - were they?

[Susanbuckler]

David
All the molds have little holes in them & the holes are clear.
Are molds always supposed to be put on kiln furniture? Oh dear.....somehow I missed that

[Marty]

You just don't want to trap air between the mold and the shelf but that's very unlikely as they don't sit perfectly flat so the only reason for furniture is to get the mold closer to the top element.
We do get earthquakes in the Hudson Valley (I'm across the river and south a bit) but not enough to do that kind of movement. The selective nature of the "event" puzzles me.

[Susanbuckler]

Marty
There was an earthquake a few years ago that rattled the windows in my office in Kingston ...very spooky.
Should I put my molds on kiln furniture when I slump?
I have not done that....everything so far seems to slump well.....except these little two 3 x 3s

[bob proulx]

Hey, some times shit happens and we will never figure it out.
Bob