Complex sentence: Staff is chiefly made of powdered gypsum or plaster of Paris, with a little cement, glycerin, and dextrin, mixed with water until it is about as thick as molasses, when staff is cast in molds it can form any shape.
Split into simpler sentences: Staff is chiefly made of powdered gypsum or plaster of Paris, with a little cement, glycerin, and dextrin, mixed with water until it is about as thick as molasses. When staff is cast in molds it can form any shape.