There are several suppliers of stainless steel and ceramic formers for pot melts. They are not always necessary.
If you only want a circle, you do not need a former at all. The shelf must be kiln washed and level. The glass will pool in a circular manner ranging in thickness – thickest at the centre and 6-7mm at the edge. The variation in thickness depends on the time the glass is kept at the working temperature after the pot has emptied.
If you are wanting a thicker melt, you do need a dam of some sort. You can purchase what you want, or you can make some from the materials you have at hand.
You can make a rectangle or square melt from existing straight dams. You need to make sure the dams are kiln washed and lined with 3mm fibre paper. You do not need to cut the dams to a predetermined length. Instead, you can arrange them so that one end of the dam starts at the edge of your rectangle. The next dam is butted at right angles to the first at the length wanted. The other pieces are fitted similarly, until the last one passes the end of the first, so that they are butted together. Then line with the fibre paper. If you feel the dams are too light, you can back them up with bricks to prevent movement.
Using fibre paper, fibre board, or vermiculite board you can make any shape of melt that you can cut out of these materials. If you don’t have refractory board, you can make your former out of layers of 3mm fibre paper. It is possible to make a template for cutting of the multiple layers. Cut your shape from the required number of layers of fibre to be as thick as your pot melt will become, according to your calculations. Pin these layers together with stainless steel pins to be sure they do not move or float with the glass. If you like, you can weight the layers of fibre paper with kiln furniture.
If you have refractory board – fibre or vermiculite – you can cut the required shape from them. If you do not harden the fibre board, you do not need any further separator. But you can line the shape with a thin fibre paper to ease the release and refine the edge. Vermiculite always needs a separator, as it sticks to glass. You should line the vermiculite board to get an easy release from the glass.
Using refractory materials releases you from the restrictions of commercially available forms and allows your imagination to take over. It may not be cheaper than the bought ones, but will have the greater feeling of achievement. In addition, you can develop all sorts of forms and depths not thought of by the commercial suppliers.