Seals were used to authenticate or validate documents, sometimes in place of a signature. They were also used to physically seal items of importance.
The term 'Great Seal' is given to seals used by monarchs, which were held in the custody of the Chancellor. A new Great Seal was made for each reign, with old seals ceremonially broken up once the reign had ended.
Seals on documents were usually made of beeswax. To make the seal, a 'matrix' was required - this was usually cast in bronze, although silver (and even gold) was used for Great Seals.
Seals were either applied directly to the document or, in the case of pendant seals, were attached to documents with silk or hemp cords, or strips of parchment. Pendant seals were double-sided, consisting of the obverse (the face) and the reverse.
The seal shown is a Great Seal of Henry VIII (E 329/475). The obverse shows Henry on his throne, complete with orb and sceptre, while the reverse shows Henry charging into battle astride his horse. The seal was used on a letter from Henry to Edward Seymour, a knight, in which he granted an annuity of 50 marks.