The characteristics that distinguish fine crystal are apparent to the naked eye. Possible imperfections include frosting, milkiness, cloudiness, bubbles, chips, scratches or inclusions. What you want to see is a reassuring absence of flaws, perfect clarity, silky smooth surfaces and a mesmerizing display of prismatic fire. You will, if it's a Schonbek. Lead content is not necessarily a guarantee of fine quality crystal.
Lead simply acts as a softening agent, making glass easier to cut and polish.