Making a silicone mould

This page has safety advice that hasn't yet been checked by our safety reviewer. Treat it as general guidance, and follow your game's, venue's or product's own safety rules first.

An introduction to making a silicone mould of an original piece, for costume makers who want to cast repeat copies of prop and armour details.

A silicone mould lets you capture the fine surface detail of an original sculpt or found object and then cast copies in resin, foam clay, or other materials. Once the mould is finished it can be used many times over, which makes the effort worthwhile whenever you need several identical pieces — repeated armour scales, decorative buttons, or small prop ornaments, for example. The broad process starts with preparing your original piece, sometimes called the master. You clean it thoroughly and apply a release agent if the surface could bond to silicone. Then you build a containment wall around it — cardboard, foam board, or purpose-made clay borders all work — and pour or brush liquid silicone rubber over and around the piece. The silicone settles into every crevice and cures to a flexible rubbery solid. Cure times vary a great deal between products, so follow the specific instructions on your silicone rubber rather than relying on a general figure. Some silicones will not cure properly against certain modelling clays, latex gloves or uncured 3D-print resin, so check your product's list of materials to avoid and test on a scrap if you are unsure. Complex shapes sometimes need a two-part mould, where you pour one half, let it cure, flip the piece, and pour the second half after applying a parting agent so the two halves release from each other cleanly. Once the mould is open and the master removed, you have a negative impression ready for casting. Test your first pour with an inexpensive material before committing to resin or expensive foam, so you can spot any air bubbles or thin spots in the mould walls. Small bubbles in the silicone surface can often be reduced by brushing a thin layer onto the master first and letting it settle before the full pour. Working with silicone rubber and any associated casting materials calls for careful safety habits. Many silicone systems and the resins you may later pour into them release fumes that can irritate the lungs or skin; work in a space with good fresh-air ventilation and wear a respirator fitted with the correct cartridges for organic vapours rather than a basic dust mask. Nitrile gloves protect your skin, and safety glasses guard against splashes. Younger makers should work alongside an experienced adult. Check the safety data sheet for every product you use, as hazard levels differ between brands and formulations.