Stuck Mold

[Norton Caff]

I'm a beginner. I've successfully done a fuse using System 96 and then wanted to slump the results. Two slumps were over glass vase molds
The result seems to be a common problem according to Google. One item snapped as it cooled and with the other the glass is stuck on the mold. I had used shelf primer on the mold. I did use some fire paper on the top of the mold but didn't use enough, obviously. I'm learning the hard way. I have tried hot water to heat the glass but this hasn't worked. So I'm up for propping the glass upside down and heating the kiln until the mold drops out as I've read about this.

My question is what temperature should I take the kiln to and at what speed?
Any help would be gratefully received.
Cath

[Pat from Canvey]

Could you post a picture as it might help to determine why the glass is stuck to the mold. Are there any undercuts for example? Did you mean propping the glass and mold upside down and heating till the glass seperated from the mold?

[Jane C ♫]

Is it a stainless steel mould?

It sounds like you might have fired them for too long ... did the glass flow right down to the bottom of the mold and underneath? Is the glass melted fairly smoothly to the mold all the way down?

If you melted the glass over the top of the mould and it has stuck (with the mould inside), but with a clear passage for the mould to come out again, then I'd try turning upside down and filling with iced water instead as that will shrink the metal and might help you to get it out.

Sanding your metal mould before priming helps the primer to stick - they do suggest half a dozen coats.

If you value your mould more than your vase, then I'd tap it with a hammer and see if you can break it free. Otherwise, does it work as a vase with built in metal flower receptacle?!

With the one that snapped, it's possible you had it too close to the kiln elements and the heat difference between the top and bottom of the piece, especially in a top element kiln, was possibly too much for it. Try a slower cooling ramp next time as that will help to even things out.

I don't take my kiln much above 650-670C when slumping (that's for Bullseye - check out Spectrum's website for the correct slumping temps and firing cycles which won't be far off that) - if you want it to move further, hold it for longer at that temp as you have more control over the outcome when it's moving slower.

Do you have suitable gauntlets / apron / goggles for having a very brief peek in the kiln when it's up at that temperature? If so, having a one second peek (just crack the lid a hint, don't open it right up) will give you an idea about whether the piece has slumped enough to be ready to move on to the next part of the cycle.

Your best bet is to start with a fairly lightly slumped handkerchief style vase and then work up from there - remember you can always put the piece in again and melt it a bit more if it comes out underdone!

Hope that helps!

Jane.

[Norton Caff]

Thanks for your replies.
It's a ceramic mold. Would ice work in this?
I was warned to cover the mold in paper but obviously totally underestimated things.

My firing plan was
66°C/hr to 148°C hold 15 mins
148°C/hr to 593°C hold 20 mins
66°C/hr to 677°C hold 25 min
204°C/hr to 510°C hold 40 mins
66°C/hr to 425° hold 10 mins
999°C/hr to 25°C

This schedule was given by my tutor but it differs from the one on the Spectrum 96 webpages so that's got me confused.

The mold is straight sided so I assumed I just need to get to a temperature at which the glass relaxes its grip. Just not sure how quickly to ramp it up.

I'm having difficulty posting photos

[Norton Caff]

[url href="http://www.flickr.com/photos/39800377@N08/9997437864/" title="DSC_0130 by NortonCaff, on Flickr"><img src="http://farm6.staticflickr.com/5494/9997437864_6baca00b28.jpg" width="500" height="334" alt="DSC_0130"></a>[/url]

[Pauline]

DSC_0130 by NortonCaff, on Flickr
there you are

[noora]

I've heard that for draping you should use a steel mould, since steel shrinks more than glass when it cools down. A ceramic mould won't shrink as much as the glass, so the glass gets stuck over the mould when it shrinks.

When you slump into a mould it's the other way around, you should use a ceramic mould since a steel mould would shrink around the glass and get stuck.

[Warm Glass UK]

Pricey but this is the best stuff for stainless steel mould release....http://www.warm-glass.co.uk/boron-nitride-spray-p-2993.html

[JKC]

Much cheaper here:

http://www.tempsfordstainedglass.co.uk/acatalog/Kiln_Wash_and_Nitride_Spray_.html

Janet

[Gordon]

Would it be possible to gently and evenly heat the glass with either a crafters heat gun or an electric paint stripper to try to expand the glass before the ceramic mold ?

[Norton Caff]

I'm not sure I wouldn't crack the piece Gordon.

So far I have heated it up with the glass propped so that the mould could drop out. Ramping at 80 degrees to various temperatures.
I've tried soaking but never thought that would work anyway.
Also tried to get tooth floss down the sides to see how stuck it is and it's very stuck.
Next idea is to heat upside down so that the glass tries to slump away. Failing that, its rather pretty scrap glass and a mould I won't risk again.
Cath

[Gordon]

The idea of heating with aheat gun is so the glass heats before the mold so, hopefully it will expand first. If you at the stage of binning it what is there to loose ?

**** Just as a thought how about standing it in hot water ( again so as to expand the glass )

[Zeldazog]

Heating it up with the glass propped up so the mould can drop out is unlikely to work - gravity will keep it hanging down once the glass is soft enough - you need it to fall away from the ceramic mould

Personally, I'd stick it back in the kiln upside down as it were - so the base of glass handkerchief is on the kiln shelf, and take it (slowly, slowly) up to a low slump.  Hopefully it was slump away from your mould a little, assuming it's simply grabbing and not fused on.

[Jane C ♫]

It looks like a nice piece - I can see why you don't want to lose it.

noora is right: You should always slump INTO ceramic and OVER stainless steel. Steel shrinks more than glass does, so you can get the moulds out afterwards.

However, zeldazog has a good idea - put it back in upside down for a bit - and see if you can get the glass to relax its grip on the mould... I'd just take it up to 677 as per your firing cycle, hold for 1 minute and straight down again. This should move it a bit ...

You can use a stainless steel cocktail shaker (sanded and primed) as a slump mould if you want something cheap to try as a metal one.

[Norton Caff]

Thanks Jane. I shall try that, that is what I meant really. I'm thinking of the mould being upside down. Now do I take it through the exact same firing cycle? Then after the minute's hold, how quickly do I drop the temperature?
I'm good at learning the hard way! So much for lining with fire paper!