I just found in the forums of «Verein fuer die Schwarze Kunst» some interestening links. One of it was Stan Nelson, YouTube Channel where the historian of printing history explains how type was casted for several hundred years.
As a hard contrast: Dafi Kühne shows us how he's doing it in the 21th Century. Casting Plastic Resin Type brought to you by his «Printing Show™» 🚀