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Fusing and Stained Glass Tips and FAQ's => Fusing Tips and FAQ's => Slumping => Topic started by: Sandera on February 22, 2013, 04:41:24 PM

Title: Multiple slumpings in the same mould.
Post by: Sandera on February 22, 2013, 04:41:24 PM
In my eternal quest to keep costs down I am looking at slumping 2 items (each 6mm thick) of the same shape and size, one on top of the other, in the same mould, at the same time.

Has anyone attempted this and, if so, did you have to adjust the firing schedule and did the glass remain as 2 distinct pieces or did 2 become 1 (bah! Going to have that song in my head for the rest of the day now!).

I'm going to experiment anyway but any observations would be invaluable.
Title: Re: Multiple slumpings in the same mould.
Post by: Zeldazog on February 22, 2013, 05:08:28 PM
I'd think that the underside of the top layer would afffect the top of the bottom layer, even if it didn't stick... and the two wouldn't come out the same shape (the inside of the bottom piece is smaller, all round, than the mould itself - and the shape would be slightly different too....

Can't say I've tried it and doubt I ever will.... I honestly don't think it's worth the risk of ruining two pieces of glass, (never mind potentially the mould if something went wrong) for the sake of a quid's worth of electricity - is your kiln particularly inefficient, or are your electricity costs that high?


Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 22, 2013, 05:19:48 PM
Quote from: Zeldazog on February 22, 2013, 05:08:28 PM
I'd think that the underside of the top layer would afffect the top of the bottom layer, even if it didn't stick... and the two wouldn't come out the same shape (the inside of the bottom piece is smaller, all round, than the mould itself - and the shape would be slightly different too....

Can't say I've tried it and doubt I ever will.... I honestly don't think it's worth the risk of ruining two pieces of glass, (never mind potentially the mould if something went wrong) for the sake of a quid's worth of electricity - is your kiln particularly inefficient, or are your electricity costs that high?


Thanks Zeldazog (or can I call you Zelda?!). No the kiln isn't too expensive to run but rather it's the time it takes to slump 1 piece as opposed to 2 pieces. I can only fit one, large, slumping mould in it and sometimes I have 3 or 4 pieces in a queue to go in which is a bit frustrating.

I wouldn't try it with coloured glass nor with my favourite mould. If it were to be successful then that might be pretty useful.
Title: Re: Multiple slumpings in the same mould.
Post by: ♥♥Tan♥♥ on February 22, 2013, 05:21:08 PM
Well Dawn has summed up all the important stuff and now I am just having a good old muse because I had never thought of this and its an interesting question..

Would you put a layer of thinfire between them to stop the pieces sticking together because if you did that would add onto the cost immediately.

I would GUESS that the bottom layer would be more of a defined shape with acuter angles than the upper piece but if you slump one on top of the other as Dawn has said  you will lose the gloss on the top of the lower piece and end up with one muted piece and one glossy piece.

I'm really not sure about the stress on the mold, if it were stainless steel I would have a play but if it's ceramic I really wouldn't want to put it under all that stress just to see what happens, molds are blooming pricey.

Ermmm, would I adjust the firing schedule...........yes, I would probably reduce the ramp speed to about 100 to ensure a slow slump and even temp and have a longer hold time so the layers have time to think about what they are doing.

But if you have any problems with one like a bubble or a crack it is going to affect the other.

I wouldn't try this with a ceramic mold but I might with steel one, having said that I'm not sure I would want to slump two layers of 6mm each, it's interesting this, let us know how you get on, you're a pioneer my girl! ;D
Title: Re: Multiple slumpings in the same mould.
Post by: Pandanimal on February 22, 2013, 05:24:48 PM
Be very interested to see how you get on. I have never really done any fusing or slumping (the odd marble and bits of glass rod) and never used a mould.  But you sound determined to give it a try so please do show us the result, success or failure!
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 22, 2013, 05:26:54 PM
Thanks Tan. I think your concerns re using a ceramic mould are likely to be well-founded so I will try it out on a steel one and let you all know how I got on. Thanks for the tip re the firing schedule as well.

I'm really glad I posed the question as it's giving me food for thought!
Title: Re: Multiple slumpings in the same mould.
Post by: Zeldazog on February 22, 2013, 05:42:57 PM
Quote from: Sandera on February 22, 2013, 05:19:48 PM

Thanks Zeldazog (or can I call you Zelda?!). No the kiln isn't too expensive to run but rather it's the time it takes to slump 1 piece as opposed to 2 pieces. I can only fit one, large, slumping mould in it and sometimes I have 3 or 4 pieces in a queue to go in which is a bit frustrating.

You can call me Zelda (it originates from Terrahawks not the Nintendo game); or Dawn  ;)

I get what you mean about the frustration of only fitting in one mould at a time and the wait, but at least you can set it and walk away and do something else.    The trouble would come if you start getting more orders per week than you can physically fuse and slump in a week.

Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 22, 2013, 06:22:21 PM
Quote from: Zeldazog on February 22, 2013, 05:42:57 PM
Quote from: Sandera on February 22, 2013, 05:19:48 PM

Thanks Zeldazog (or can I call you Zelda?!). No the kiln isn't too expensive to run but rather it's the time it takes to slump 1 piece as opposed to 2 pieces. I can only fit one, large, slumping mould in it and sometimes I have 3 or 4 pieces in a queue to go in which is a bit frustrating.

You can call me Zelda (it originates from Terrahawks not the Nintendo game); or Dawn  ;)

I get what you mean about the frustration of only fitting in one mould at a time and the wait, but at least you can set it and walk away and do something else.    The trouble would come if you start getting more orders per week than you can physically fuse and slump in a week.


That's the problem Dawn! I'm trying to balance the viability of the business whilst growing it at a sustainable rate. I'm finding it quite difficult to keep up with things at the moment whilst also giving myself time for development and experimentation. And the profit margins are very tight. Maybe I just need to acknowledge that I'll be lucky to break even  :'(

Anyway this idea is a bit of a shot in the dark but I'll happily share the results.
Title: Re: Multiple slumpings in the same mould.
Post by: ♥♥Tan♥♥ on February 22, 2013, 06:27:48 PM
Playing and experimenting is learning ;)
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 22, 2013, 06:31:46 PM
So much to learn, so little time :)
Title: Re: Multiple slumpings in the same mould.
Post by: Glyn Burton on February 22, 2013, 08:11:37 PM
Molds normally have a small breather hole which allows the air to escape as the glass slumps in. I would have thought that there would be a strong possibility of air being trapped between the two sheets of glass and blowing bubbles.
Title: Re: Multiple slumpings in the same mould.
Post by: firedinglass on February 23, 2013, 08:35:02 AM
 iI just don't think this will work. The shape will not be true on either, the polish will be non existent on the top side of the under dish and the  top dish will not have a flat base. ...
Title: Re: Multiple slumpings in the same mould.
Post by: MeadMoon on February 23, 2013, 11:30:37 AM
I also have doubts about it working for two separate pieces, but it could produce something quite original - although not what was intended.  I'll be very interested to see what happens if you do decide to try it.
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 23, 2013, 08:48:51 PM
Quote from: Glyn Burton on February 22, 2013, 08:11:37 PM
Molds normally have a small breather hole which allows the air to escape as the glass slumps in. I would have thought that there would be a strong possibility of air being trapped between the two sheets of glass and blowing bubbles.

That's true Glyn. Mmm....this is looking distinctly less feasible. But ....I'm going to try it anyway just so we know!
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 23, 2013, 08:55:04 PM
On another note re slumping: I'm doing a short mould making course and the tutor is eager to personalise the session to include mould making for glass. I think the others on the course are ceramicists. I suggested that it would be useful if I could make a couple of slumping moulds. Does anyone know what material commercial slumping moulds are made of? Is it clay?
Title: Re: Multiple slumpings in the same mould.
Post by: Pat from Canvey on February 24, 2013, 08:08:02 AM
I've used clay to make a mold but there are proprietory brands also. Have a look at, I think it's Alec Tiranti,
http://www.tiranti.co.uk/
Title: Re: Multiple slumpings in the same mould.
Post by: Lilley on February 24, 2013, 08:10:58 AM
I've slumped two separate layers of glass over the same shapes at the same time.  I went on Jacqueline Cooley and Joanne Newman's sledge and slump course at Warm Glass a while back.  We made plaster formers and slumped glass over them.  I cut two circles of float glass and stacked them with plaster of paris in between.  They did separate, the inner one next to the 'mould' is sharper, more defined as you'd expect, but the top suface is affected by the plaster and glass above it and the top piece of glass is more rounded.  Obviously they do stack and Jacque and Jo had some pretty examples of float that they had layed up to make stacked vessels/sculpture.  The glass was 4mm thick.  You do have to be careful to cover all of the bottom piece with the plaster otherwise they will stick together forever! If you go to Warm Glass's page on facebook, https://www.facebook.com/pages/Warm-Glass-UK/121265261263687?v=wall and look for the sledge and slump course photos you'll find some pictures of what we did. If you look at the ones of the kiln set up in one of them you'll see on the left towards the back a circular looking arrangement - that was my double stack of glass.
Title: Re: Multiple slumpings in the same mould.
Post by: Glyn Burton on February 24, 2013, 08:39:43 AM
You can use pretty much any clay to make a mould just bisque fire it. I tend to use a fairly high temperature say 1050c which will give a good balance between strength and porosity.
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 24, 2013, 05:44:02 PM
Thank you for help and advice. Lilley that sounds like an amazing class. Do you have a photo of the finished pieces? Glyn -thanks - I can now advise my tutor. I assume you drill the air hole after firing and then smooth off? Pat thanks for the recommendation re tiranti - looks as though it stocks everything I need!
Title: Re: Multiple slumpings in the same mould.
Post by: Glyn Burton on February 25, 2013, 08:12:12 PM
Make the air holes when the clay is leather hard its easier and then fire. do you want photos of the moulds or the finished pieces?
Title: Re: Multiple slumpings in the same mould.
Post by: Sandera on February 26, 2013, 05:58:53 PM
Thanks again Glyn - that's what I'll do. If you wouldn't mind sending photos of both that would be great!
Title: Re: Multiple slumpings in the same mould.
Post by: chas on March 05, 2013, 09:04:18 AM
Quote from: Sandera on February 23, 2013, 08:55:04 PM
On another note re slumping: I'm doing a short mould making course and the tutor is eager to personalise the session to include mould making for glass. I think the others on the course are ceramicists. I suggested that it would be useful if I could make a couple of slumping moulds. Does anyone know what material commercial slumping moulds are made of? Is it clay?

Well, the white ones are ceramic rather than clay I think... the closest I've got in a home-made mix is 50/50 plaster of Paris and silica. The first for setting and the second for durability. It gives a good smooth finish (if you want it) and rapid setting - though do allow thorough drying out to avoid self-destruction. Of the mould, that is.


Chas
Title: Re: Multiple slumpings in the same mould.
Post by: Lilley on March 05, 2013, 11:50:33 AM
Chas, ceramic = fired clay  ;D