Decorative brass disc.

It is unknown what this disc was, it may have been a decorative item from a uniform or from furniture.  It may be from the Armada wreck but could also easily be from the later 18th century wreck of the Lady Margaret.   In the eighteenth century, brass objects were generally made through a process called sandcasting, where a mould is made by packing fine-grained silica sand around a pattern of the object to be cast. As the sands used in the eighteenth century were extremely fine, it was possible to cast very fine detail, such as the exquisite work on one of the hinges.