Things You'll Need
Fine molding plaster
A key mold is used to make a copy of a key by pouring a liquid that will harden, like silicone, into a form in the shape of the key to be copied. You can make a key mold to copy simple keys with teeth but no grooves using only a few simple materials. The mold is formed in a manner similar to the one you would you use to create molds for other small items, like cup handles and small hardware parts.
Roll out a piece of fine molding plaster with a rolling pin, so it is 2 inches thicker than the thickness of the key you want to make the mold from. The piece of plaster should be several inches wider and longer than the key.
Grease the key so it will release from the plaster easily. Make sure you are thorough along the edges and on the teeth of the key.
Press one side of the key into the piece of plaster until the plaster and the key are perfectly even. Do not push the key in farther than this or your mold will be too deep.
Pull the key out of the plaster, being very careful not to disrupt the imprint you made.
Let the plaster dry until it is completely hardened before using the mold.
You can use any moldable material as long as it hardens to a smooth finish.
Make sure you clean the key you used to make the form afterwards or stray bits of plaster may get stuck to it and affect its performance.