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Cold casting makes a metal-looking prop without melting metal: mix metal powder into clear resin, pour it into a mold, then finish the cured surface. The result is a resin-bound composite with metal powder—not a solid metal part. In Make:’s example, powdered iron and polyester resin produce a magnetic, weathered-looking robot head.
What cold casting is—and what it is not
In the technique described by Make:, metal powder is mixed with clear resin and cast in a silicone-rubber mold. Because the metal is not melted, there is no forge or molten-metal pour. But the casting materials still require care: resin, catalyst, powder and mold products each have their own handling requirements.
The finished object is a composite. Its resin provides the shape, while metal powder at the surface helps create a metal-like appearance and can respond to a magnet. It should not be treated as equivalent to a solid metal casting in strength, heat tolerance or other performance; the tutorial does not establish those properties.
Materials and setup for the demonstrated method
Make:’s March 2016 example, by Jeremy S. Cook, follows a Mold3D video demonstration by Paul Braddock. It uses a 3D-printed robot-head master to make a silicone mold, then casts the piece using polyester resin and powdered iron.
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- Master: a model of the object to reproduce; the example uses a 3D-printed robot head.
- Mold: silicone rubber. The project names Pinkysil and reports that it set in about 20 minutes.
- Casting mix: clear polyester resin and powdered iron. The example reports a 1:1 ratio; this is a project-specific choice, not a universal recipe.
- Release and finish: mold-release spray, steel wool and a rust-catalyst solution are used in the tutorial.
- Protection: gloves and any eye, ventilation or respiratory protection specified by the current safety documents for the products you select.
How to make the cold-cast piece
- Make a mold from the master. Place the master in a mold-making setup, apply the selected silicone according to its instructions, and allow it to cure. In Make:’s example, Pinkysil set in about 20 minutes. Remove the master once the mold is ready.
- Prepare the casting materials. Check the resin, metal powder and mold manufacturers’ current technical instructions for compatibility, mixing, handling and cure requirements. The tutorial combines polyester resin and powdered iron at 1:1, but that ratio should not be transferred to different products without their instructions.
- Apply mold release and pour. The example applies mold-release spray before pouring the mixture into the silicone mold. Follow the selected release product’s directions and avoid introducing contamination into the casting mix.
- Allow the resin to cure, then demold. Make: reports removing its cast after around six hours. That timing belongs to this particular project, not to resin products generally. The finished example had a few small air bubbles.
- Work the surface. Burnish the cast with steel wool, apply a rust-catalyst solution for a weathered appearance, then burnish again with steel wool and the back of a spoon, as described in the tutorial.
Safety: follow the documents for the actual products
“Cold” means the metal is not melted; it does not mean the process is hazard-free. Make:’s general resin-casting guidance advises ventilation or an appropriate respirator, gloves, keeping children and pets out of the work area, and reading the supplied safety data sheets. These are editorial precautions, not a substitute for current manufacturer instructions. Before mixing, consult the safety data sheets and technical documents for the exact resin, powder, catalyst, silicone and release product in use, and use the protection they specify.
When to choose another process
When you need an actual metal part
Cold casting is suited to a metal-like finish without melting metal. If the object must be metal, a hot-metal process is different: Make:’s desktop-foundry project describes Field’s metal, an alloy of bismuth, indium and tin, with a stated melting point of 144°F (Make: Desktop Foundry). A separate pewter prop project gives a melting range of 170–230°C (338–446°F), depending on alloy mixture, and involves heating and pouring pewter (Make: Beskar Ingots & Witcher Coins). Neither is cold casting; both involve hot metal and require appropriate equipment and precautions.
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When you need a large, hollow prop shell
Rotocasting, also called slush casting in this context, is another resin approach: resin is moved around inside a mold to form a hollow shell. Make: describes it for lightweight prop construction, but it does not provide the metal-powder surface used in the cold-casting example (Make: Rotocasting).
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choosing materials without assuming compatibility
The tutorial establishes one specific combination—powdered iron with polyester resin—not a general compatibility rule for metal powders and resins. Check the selected products’ technical documents before buying or mixing them. Resin cure behavior, usable ratio and mold compatibility depend on the specific products; the tutorial’s reported 1:1 mix, roughly six-hour demold and roughly 20-minute mold setting should not be used as product specifications. For general moldmaking considerations, see Make:’s Primer — Moldmaking. Its resin-casting safety guidance is available in Casting Resin Rings.
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