Many ceramic plant pot saucers can be used as circular moulds. Most are unglazed and will accept kiln wash easily. Some are unglazed, but polished to such an extent they are no longer porous. These and glazed flower pot saucers need some preparation before applying kiln wash.
|Plant pot with saucer|
Polished and glazed saucers require roughing to provide a key for the kiln wash solution to settle into. This can be done with normal wood working sand papers. You may want to wear a dust mask during this process, but not a lot of dust is created. You could also use wet and dry sandpaper or diamond handpads with some water to reduce the dust further.
If the sanding of the surface does not allow the kiln wash to adhere to the saucer, you can heat it. Soak it at about 125C for 15 minutes before removing it from the kiln to get the heat distributed throughout the ceramic body. One advantage to the ceramic is that it holds the heat, because of its mass, for longer than steel. Apply kiln wash with a brush or spray it onto the warm saucer. As it dries, apply another layer of kiln wash. Two or three applications should be enough to completely cover the surface. If not, then you probably will need to heat up again before repeating the process.
Alternatives to plant pot saucers
There are alternatives to the saucer approach to getting thick circles from a pot melt.
You can cut a circle from fibre paper and melt into that. The advantage of fibre paper is that it requires little preparation other than cutting and fixing. You may have only 3mm fibre paper and want a 9mm thick disc. Simply fix the required number of layers together with the circle cut from each square. The fixing can be as simple as sewing pins, copper wire, or high temperature wire. Then place some kiln furniture on top of the surrounding fibre paper to keep it in place on the shelf during the melt. This furniture can often be the supports for the melt.
If you find cutting multiple circles of the same size a nuisance, you can use fibre board. Simply cut the circle from the board with a craft knife. You will probably want to line the circle with fibre paper, as the cut edge of fibre board can be rough. Alternatively, you can lightly sand the edge. Wear a dust mask and do this outside, if possible, to keep the irritating fibres away from the studio. If you want a thicker melt than one layer of board can give, just add another in the same way as for fibre paper.
In both these cases, you may wish to put down a layer of 1mm fibre paper to ensure the glass does not stick to the shelf and does not require sandblasting.
The advantage of the fibre paper or board alternative to flower pot saucers is that you do not need to kiln wash anything unless you want to. If you do not harden the fibre paper or board, it will not stick to the glass.
Another alternative is vermiculite board. The advantage of this is that it comes in 25 and 50 mm thicknesses, so you can make the melt as thick as you like without having to add layers. You can cut the vermiculite board with wood working tools. Knives will not be strong enough to cut through the vermiculite board. You will need to kiln wash or line the vermiculite with fibre paper, as the board will stick to the glass without a separator.
Of course, if you want a circle without concern over the thickness, you can do the melt without any dams. You need to ensure that the shelf is level. Any supports for the pot will need to be both kiln washed and far away enough that the moving glass does not touch the supports and distort the circle. In general, one kilogramme of glass will give a 300mm circle, so your supports need to be further apart than the calculated diameter of the circle. An undammed circle will vary from 6mm at the edge to as much as 12mm at the centre, depending on temperatures and lengths of soaks.