I used a hard setting dental plaster to make the molds. Unbeknownst to me, it take around 40 minutes to get to a decent consistency like double cream. I use the back of my hand to flick plaster onto the model. This helps to not capture any air bubbles on the sculpure. As the plaster thickens, I pay special attention to those areas would are like to problematic, ie. deep set wrinkles, inside the mouth/ears.