Things You'll Need
Silicone rubber mold kit
1/8-inch diameter wire, 4 inches long
Creating your own duplicate of a coin means making a mold out of silicone rubber. You will need to make a two-part mold of your coin in order to capture the detail on both sides. Silicone rubber is ideal because it captures fine details and is very durable. However, you will not be able to use high-temperature metals to cast your copy. Instead, with this mold you can create resin or tin duplicates of your original.
Spread the newspaper over your workspace and don your gloves and face mask. Take a chunk of plasticine and roll it into a sphere the size of a golf ball. Place it on the newspaper.
Lay a sheet of plastic wrap over the ball. Take a heavy book and press down on the ball to squash it into a flat disc that is 1/2 inch thick. Remove the book and the plastic wrap.
Place your coin in the middle of the plasticine disc and press it until it is half submerged. Use your fingers to pinch the plasticine around the coin toward its rim, closing any gaps between the clay and the coin.
Roll out two balls of plasticine the size of marbles and cut them in half. Arrange each half-sphere around the coin.
Embed the 4-inch long wire in the plasticine, connecting one tip to the coin and letting the other tip hang off of the plasticine bed. The wire will create a hole in your mold through which you can pour your casting material.
Create a wall of plasticine around the disk that is 1 inch high and 1/4 inch thick. Make sure there are no holes in the barrier.
Take one of the two bottles that come with your silicone kit and pour enough liquid into a mixing cup to potentially half-fill the plasticine bed.
Pour an equal amount of liquid into a second mixing cup from the second bottle. Then pour the two liquids into a third cup and stir it with a popsicle stick for one full minute. Pour the mixture into the plasticine bed and let it cure for 24 hours.
Flip the mold over and peel the plasticine away to reveal the other side of your coin. Be sure to peel the four round plasticine lumps away, too. Leave the wire in place. You will now make a mold of this side of the coin.
Build a 1/4-inch thick wall of plasticine up around your mold so that it stands 1 inch above the surface of your coin. Make sure there are no holes in it.
Paint liquid wax across the silicone rubber around the coin and wire. This will keep the two parts of the mold from sticking together.
Make a second batch of silicone rubber exactly as you did the first batch. Pour it over the coin. The plasticine walls will keep it from overflowing. Allow the mold to cure for 24 hours.
Silicone curing time varies by brand. Check your packaging for an accurate estimate.
Do not inhale the silicone fumes or expose your skin to it. Do not leave the silicone in a place where children or pets may get at it. Work in a ventilated area.