Orichalcum Bars are the replacement for Mythril Bars in 1.2. To unlock them, the player must destroy a Crimson Altar or a Demon Altar in Hard Mode, mine the new ore, and smelt it. They have (nearly) the same properties as Mythril bars do, but are bright pink/violet instead of pale green and can, like the other updated/new ores, be placed in the same semi-background layer as Wooden Beams; as such they can be placed in the same space a background wall is in and can be passed through, but cannot be placed in the same space as a block. Their sprite occupies a 1x1 space.
The word Orichalcum comes from the ancient Greek term oreikhalkos, which means mountain copper. It was described as being second only to gold in value, and probably referred to brass, amber or a gold/metal alloy.