Step 3: Spray a coat of primer over the boxes to ensure that any super glue used during construction of the bases or the boxes is covered. Superglue will cause the silicone to cure badly, leaving soft uncured goop where it touches.
Step 4: Mix your silicone. I used two different types of silicone here, one that cures in 6 hours and another that cures in a slightly shorter time. I believe the purple dense one is OOMO 30.
Step 5: After waiting over night, release the silicone from the mould. Try to save your masters. They can be used if desired. (I won't, my masters get dumped straight into storage)
Step 6: Using Excalibur dental plaster start pouring bases. The key to a nice flat base is to overfill it and then after the plaster has started to separate from the water and sink into the moulds, to gently scrape the surface using a flat edge.
Step 7: Paint. The small 25mm base on the right is one of the new bases. The 50mm base on the left is one of my old bases from several years ago. The 25mm base wasn't even primed. That cement is raw plaster with a dose of Secret Weapon Miniatures Green Earth pigment washed over the top. I then went back and scraped the base with an x-acto knife to add some designs.