Glass casting mould

[Sandera]

I recently made a series of cast glass stones to form a cairn for a commission. I made each stone in clay, creating a mould for each one and cast. With all of the setting up and subsequent grinding and polishing it was a lot of work (although worth it from a developmental pov). However it occurs to me that maybe there's a better way? I've got a pyramidal casting mould that can be repeatedly used at casting temperatures -  http://www.warm-glass.co.uk/images/pdfs/Bullseye%20P&T-%20Mould%20Tips-Pyramid%20Casting%20Mould%208948.pdf

I'm wanting to make my own mould (stone shaped with a flat base that I'll probably grind to create curve sides) that I can use over and over again. In my search for a suitable material I've come across Amaco No. 25 clay. I'm wondering whether this might be durable?

Has anyone used it (or anything else) that has given you a good result? Any suggestions are very welcome.

Thanks in anticipation.

Sandera

[Warm Glass UK]

If you want to repeat a piece several times, have you considered using Castalot? You could develop several different moulds so that all of the pieces aren't identical and this would allow you to make lots from one mould?

http://www.warm-glass.co.uk/castalot-p-2627.html

[theflyingbedstead]

I've been experimenting mouldmaking with a basic buff stoneware clay, (at ceramics evening classes) and so far so good. The only problem is that you will need a ceramics kiln (that fires 1260 degrees C) to fire it.

[Glyn Burton]

One way of doing it is to form the stone shapes in wax and then investing them in a 50/50 silica flour and casting plaster mix.
The wax can be steamed out of the plaster and reused (buy it from Tiranti's)
If the moulds are large put a thin coat of the 50/50 mix over the wax form and then make a plaster and chopped fibre glass jacket to give strength.
The moulds can only be used once but the mould waste (ludo) can be recycled if mixed with plaster/fibre glass for mould jackets.

[Sandera]

I've been experimenting mouldmaking with a basic buff stoneware clay, (at ceramics evening classes) and so far so good. The only problem is that you will need a ceramics kiln (that fires 1260 degrees C) to fire it.

I don't have a ceramics kiln so stoenware isn't an option but the No. 25 clay is low fire (not quite sure yet how low). If it's low enough for my glass kiln I think I'll give it some serious consideration. I'll share the results.

[Sandera]

One way of doing it is to form the stone shapes in wax and then investing them in a 50/50 silica flour and casting plaster mix.
The wax can be steamed out of the plaster and reused (buy it from Tiranti's)
If the moulds are large put a thin coat of the 50/50 mix over the wax form and then make a plaster and chopped fibre glass jacket to give strength.
The moulds can only be used once but the mould waste (ludo) can be recycled if mixed with plaster/fibre glass for mould jackets.

Glyn I've been considering having a go at the lost wax process for ages now and I agree that it's something I must have a go at. I'm being a bit lazy though as I want to avoid the process of cottling up (when I can). The initial stones were quick to create so that's not the problem. It would take me less time (I'm very slow and messy!) to create a mould of the same quality as the pyramid mould and then reuse it. That's the plan anyway.....

[Sandera]

If you want to repeat a piece several times, have you considered using Castalot? You could develop several different moulds so that all of the pieces aren't identical and this would allow you to make lots from one mould?

http://www.warm-glass.co.uk/castalot-p-2627.html

I think I tried it once (quite early on in my experimentation) and didn't get the results I wanted. More my fault than the product's. I've got some left so I'll have a play!

[Warm Glass UK]

Give us a call and talk to Megan if you need any help (01934 863344)

[Sandera]

Give us a call and talk to Megan if you need any help (01934 863344)

Okay - I may just do that. Thanks 

[Zeldazog]

I don't have a ceramics kiln so stoenware isn't an option but the No. 25 clay is low fire (not quite sure yet how low). I

What's No 25 clay?  Trouble is, if it fires low, it won't stand up to casting temperatures. 

You could look at terracotta clay - not 'quite' as robust as stoneware, but it biscuit fires at around 800 deg C and high fires at 900 to 1000 - I am not sure how well biscuit fired terracotta would stand up to repeated casting temperature firings, but I used bisque terracotta moulds for slumping, and they'd been around at college for several sessions beforehand.

[Sandera]

I don't have a ceramics kiln so stoenware isn't an option but the No. 25 clay is low fire (not quite sure yet how low). I

What's No 25 clay?  Trouble is, if it fires low, it won't stand up to casting temperatures. 

You could look at terracotta clay - not 'quite' as robust as stoneware, but it biscuit fires at around 800 deg C and high fires at 900 to 1000 - I am not sure how well biscuit fired terracotta would stand up to repeated casting temperature firings, but I used bisque terracotta moulds for slumping, and they'd been around at college for several sessions beforehand.

It's Amaco No. 25 and apparently fires at cone 5 but that's as much as l I know about it really - just stumbled across a reference to it when searching for casting moulds. I got a bit excited until I realised that, even at low fire, it needs to fire higher than my glass kiln can manage.

Great tip re biscuit fired terracotta though, even if I restricted myself to using them for slumping that would give me more options and solve another problem I've been pondering over. The trouble is that I'm not a ceramicist so I think anything  make will be pretty amateurish!