This shell is known as the Purple Dye Murex Bolinus brandaris, and it produced one of the most expensive dyes found in ancient times. The colour is known as Tyrian Purple, and was used by the Phoenicians and Romans. This dye was used to create royal and priestly garments, as up to 10,000 shells would be needed to dye just 1kg of wool. In nature the mollusc produces this chemical to scare away predators, and is a milky colour when submerged in water. When dried in air it turns a dark purple.
Posted by Clare but written and researched by Lisa French (biology intern, Spring 2010) who worked diligently on the wonderful conchology collections held at Leeds Museum Discovery Centre.