This post is not about the materials that go into the making of glass, but about ways of forming glass once melted or dripped into a space.
Formers are a bit different from moulds. They are more like the formers used in concrete structures – they are there to resist the movement of the contained materials and give the form or shape desired rather than a natural flow.
These formers can be of anything that can resist the firing temperatures of the process. Some of the materials are stainless steel, ceramics, fibre board and paper, vermiculite, kiln brick, and I am sure there are others.
Most of these require a separator between themselves and the glass. The ones which do not are untreated refractory fibre board and fibre paper.
Most paper is not sufficiently strong to stand on its own. Instead it is used flat and the shape cut out of it. It can be made in several layers and pinned together to achieve the height desired. It should be lined in the interior with a thin fibre paper to avoid seeing the layers of the former in the edge of the glass.
For thicker work, fibre board can be used with the shape or form cut from it. Alternatively, it can be used on its side backed up by kiln brick or other material to resist movement. More information on methods and safety are here.
If hardened, refractory board and paper will need separators between glass and former, just as most other materials will.
Sometimes the fibre board and fibre paper are not heavy enough to resist the flow of the glass. You can use weights to help resist the movement. At other times, the glass flows under the fibre and then you need something heavier. Fortunately, there are a number of refractory materials that can be used.
Other common formers
Vermiculite board is another refractory material that can be cut and shaped much like fibre board. The vermiculite needs to be covered with kiln wash where it might come into contact with glass or be lined with fibre paper or another separator.
Calcium silicate board can be used in much the same way. It also needs a separator but does not stand up to such high temperatures as vermiculite.
Ceramics, especially in the form of cut up kiln shelves can be used as straight formers. They have the advantage, over refractory fibre paper and boards, vermiculite and calcium silicate, of being heavy. They can resist the movement of thick glass. They need to have a separator and usually a 3mm fibre paper, cut 3mm shorter than the final thickness of the piece, will provide the cushion in the movement that the glass needs.
Kiln brick is an often forgotten former. The bricks can be cut and formed in many ways, even if not so freely as fibre board and paper. The bricks do need fibre paper separators to keep the glass from getting into the pores of the brick.
Stainless steel is a common former too. These are usually formed into an already determined shape and so are not so adaptable as many of the other formers. Steel contracts much more than glass and needs a cushion of fibre paper, usually 3mm thick to avoid sticking to the glass.
More information on most of these formers can be found here.