HIRST ARTS CASTS - Skullcrafts is a fully licensed seller of Hirst Arts casts. All Hirst Arts blocks offered through Skullcrafts are made exclusively from gray Merlins Magic die stone plaster unless otherwise noted. Below are the molds we offer as casts. Be aware that you are not buying Hirst Arts molds, you are purchasing plaster casts of Hirst Arts molds. Each mold comes with three options; one cast, three casts and five casts.