Here the silicone cast is remover and turned over. There is less than 1% shrinkage of the silicone. Measurements can be taken from the casting . Patterns can be drawn right from this to grind shaper knives.
To make the casting of the molding. I first took the front piece of crown off. Then I made two dams across the molding out of clay. I used a two part silicone that sets in about 4 hours. When the silicone started to set a little I placed three 1/4″by 1/4″ wooden strips to stiffen the casting.