The free-standing tombs are usually variations of either a flat-topped storage chest, or a tub with sloping sides and a convex lid of tapered decks. Ornamentation ranges from simple to elaborate. Until far in the 18th century, the most common material for a sarcophagus here was a bronze-like alloy of tin, coated with shellac. The splendid tombs of the baroque and rococo eras are made of true bronze, a nobler and therefore more expensive material. Reforming Emperor Joseph II decreed simplified burial customs for the people, and introduced the use of lighter and cheaper copper into the Imperial Crypt, where it was then used into the 19th century. In the later 19th century a mixture of cast brass and bronze as well as silver-bronzed copper was adopted. Other metals were used only rarely, except for silver and gold plating on decorations.