Complex sentence: Since the 1970s a new form of lead, restoration lead, was developed based upon the medievel lead metal composition to reproduce a more resilient product than that of the prior 100 years or so.
Split into simpler sentences: Since the 1970s a new form of lead, restoration lead, was developed based upon the medieval lead metal composition. Restoration lead reproduced a more resilient product than that in lead came of the prior 100 years or so.