Making your own clay moulds is not as difficult as often imagined. You do need to have access to a kiln that can fire to bisque temperatures, as they are above the usual limitations of glass kilns.
There are a variety of clays you can use – paper clay, school clay or any cheap clay from a ceramics supplier. Make sure any “clay” you buy from craft shops is in fact ceramic clay and not one of the no-fire or oven fire “clays”.
The method for slab moulds is fairly simple. You need to roll out a sheet of even thickness. To do this there are a few items required.
- Board to support the rolling of the clay
- Rolling pin of sufficient length
- Cloth for the bottom of the clay
- Battens of 8-10 mm thick
Place the smoothed cloth on the board.
Place or fix the battens to the width needed.
Put the clay onto the cloth and work it out to the approximate thickness you require by hand.
Use the rolling pin to complete the process by pushing the clay in front of the rotating pin to get an even thickness. This will require a number of passes, both away from and toward you. You can patch any shallow places by simply putting a small piece of clay there and going over it with the rolling pin.
At this point you can impress any design you like on the wet clay, or you can incise the leather-hard clay later.
If you are shaping the clay, you can use a variety of materials to hold the clay in the shape you want. You can use another form to support the whole of the clay if desired.
Set the clay aside to dry, ideally where air can get to all sides/surfaces. The clay will shrink during this drying process. It will take longer to dry if the clay can dry from only one surface, and it is more likely to crack. So if only one surface can be exposed to the air, you should cover the whole piece with a damp cloth to slow the evaporation from the top surface.
When the clay is leather hard, you can sand or mark the clay. Then have the clay fired to bisque temperatures. When you get the fired form back, you should sand any roughness away, as this will be the bottom surface of your completed piece.
It is important that you kiln wash or provide other separators between the mould and the glass, as the clay and glass will stick together. Because the clay and glass expand and contract at different rates, the glass will be broken or crazed by the ceramic.