Complex sentence: Flax seeds produce a vegetable oil known as flaxseed or linseed oil, which is one of the oldest commercial oils, and solvent-processed flax seed oil has been used for many centuries as a drying oil in painting and varnishing.
Split into simpler sentences: Flax seeds produce a vegetable oil known as flaxseed oil or linseed oil, which is one of the oldest commercial oils. Solvent-processed flax seed oil has been used for many centuries as a drying oil in painting and varnishing.