Lego bricks were used to build retaining walls around the parts, leaving 1/2 to 3/4 of an inch around the parts.

Soft white sulfur-free oil based clay was used to build the parting line. The clay separation must be as clean as possible to get flash-free castings later.

Once all the parts were prepared with clean parting lines and Lego walls, they were ready for silicone.

The silicone I used was a 2 part system with a 10:1 ratio by weight. After calculating the volume needed to fill my molds, I prepared the right amount of silicone.

After 24 hours, the molds were turned upside down, and the clay was removed. The silicone was uniformly coated with petroleum jelly.

Silicone will stick very well to silicone, so it's important to use the right rubber to rubber release.

My first batch of pentultimate molds were unusable because I used a universal release, and my molds glued shut.

14 individual 2 part molds were created from the machined masters.