The master from the previous posting is not finished yet, but I made another one from polymer clay and wood. I wanted to see how it would work and it turned out fine. I didn't paint this one, but varnished it with water-based varnish (solvent-based varnishes do not work on polymer clay).
After varnishing, the master needs to be treated with form separating agent, which is basically liquid wax. It will help to get the master out of the mould at the end of the process.
For the mould, I'm using Silcolan NV mould silicone. It is white and fairly thick, but it should settle well even around small objects with many details, so it should be fine. The biggest problem is the amount of hardener. Add too much and the silicone will start to harden before you're finished pouring it, add too little and the mould won't harden (or it will take very long).
After the master was treated with form separating agent and silicone and hardener mixed, it was time to press the master into the silicone. Now I just need to wait for the silicone to harden.
The next stage will be applying form separating agent over the entire surface, letting it dry and then pouring in the silicone for the other half of the mould. The form separating agent will keep the two halves separate.
Finnish post is here.