Starts from a sculpture. just clay. Usually plastic inexpensive eyes are used in the clay. then a mold is made of the clay sculpt. a silicone skin is produced from the mold, and then face paint, and punched in hair. one by one.
I noticed that on the ledger makeup, througout the movie it changes here and there. Sometimes it gets more messed up, other scenes less so. Also everyone's face is always in a constant state of change. A certain thought will change a persons face. So you get the likeness to a point, then go for the realism. Selling that it isn't a pair of plastic eyes, and rubber skin is the goal. To the extent that you think it's really him, we succeed. In the opposite direction we fail.