Although shelf paper is occasionally used to form a mold, it is normally used only on a flat kiln shelf where it provides separation so the glass does not stick to the shelf and where it provides an extremely smooth surface for the underside of the glass. It is most often used for deeply fused (fused flat) when the resulting pieces, after cooling, are used directly for jewelry. It may also be used when assembling pieces of glass into decorative laminations that are sawn apart and arranged for further fusing like making a plaid checker board or plate.
Normally, molds are painted with shelf release, also sold as kiln shelf wash. This, on drying, produces a thin, slightly dusty layer that does not do much to distort the mold shape. I only have a broad shallow knowledge of the craft, which I use for my own purposes here http://users.ticnet.com/mikefirth/warmglas.htm#BOWLMOLD and up and down that page. For more information, go to www.warmglass.com