How to Make a Steel Mold


If you would like to preserve an object or make multiples of it, you can easily cast it into steel. Steel casts make great gifts and can be poured over and over to make several copies. RTV silicone rubber is a good option for molding steel because it can reproduce a lot of detail and is inexpensive. RTV stands for room temperature vulcanizing, meaning that the rubber does not need to be heated in order to harden to a solid.

Things You'll Need

  • Object to cast
  • Box (wood or cardboard)
  • Sulphur free clay
  • Mold release spray
  • RTV silicone rubber
  • Liquid steel
  • Draw a continuous line around the object you will be making the mold from, trying to stay in the middle of it width wise. This will be the parting seam, where the mold splits so you are able to remove your cast.

  • Place the object into the box so that the parting seam line is parallel to the bottom of the box. Using small pieces of sulphur free clay, build around the object up to the parting seam line and out to the edges of the box. Smooth the clay around the parting seam as much as possible so that it is not visible on the cast.

  • Make keys in the clay. If you have a small object you can use the tip of a pencil, for a larger object use your finger to press into the clay around your object. Make three or four divots in the clay to serve as keys so that your mold will line up. Spray the clay, object and inside of the box with mold release, making sure to coat evenly and thoroughly.

  • Mix the RTV silicone rubber according to the directions on the package. Pour the rubber into the mold box so your object is completely covered and let the rubber settle for about three hours.

  • Remove the rubber, clay and object as one unit from the box and flip it over. Place it rubber side down into the box. Carefully peel away the clay and keep the object in the rubber. Spray everything with mold release.

  • Pour the RTV rubber into the mold box so that it completely covers the object. Let the rubber harden for 24 hours before removing the mold box and object and separating the mold.

  • Pour the liquid steel into the mold and allow it to harden for 24 hours. If the parting seam is visible you can sand it off using a burnishing tool.

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  • Photo Credit boot image by Aleksandr Ugorenkov from
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