This project details a mold made to cast a unicorn horn about 2' long. Inside of the horn is an insert which lights LEDs.
Oliver Tanner did most of the work here. Fun fact: we met in 2000 at a prototyping company where I was a mold maker, now I am his assistant!
The mold is made from silicone P44 and the casting is made from the same material. The trouble with using the same material (or two silicones) for the mold and the casting, is that the casting can stick to the mold permanently.
This happened to me once, and it cost $500 in material and 2 days of time. The director of the movie I was working on at the time was furious!
A foolproof way to prevent this from happening is to spray the mold with mold release, or I like to use PAM cooking spray.