A seal is a device for making an impression in wax , clay , paper , or some other medium, including an embossment on paper , and is also the impression thus made.
The original purpose was to authenticate a document, or to prevent interference with a package or envelope by applying a seal which had to be broken to open the container hence the modern English verb "to seal", which implies secure closing without an actual wax seal.
The seal-making device is also referred to as the seal matrix or die ; the imprint it creates as the seal impression or, more rarely, the sealing. In most traditional forms of dry seal the design on the seal matrix is in intaglio cut below the flat surface and therefore the design on the impressions made is in relief raised above the surface.
The design on the impression will reverse be a mirror-image of that of the matrix, which is especially important when script is included in the design, as it very often is. This will not be the case if paper is embossed from behind, where the matrix and impression read the same way, and both matrix and impression are in relief. However engraved gems were often carved in relief, called cameo in this context, giving a "counter-relief" or intaglio impression when used as seals.
The process is essentially that of a mould. Most seals have always given a single impression on an essentially flat surface, but in medieval Europe two-sided seals with two matrices were often used by institutions or rulers such as towns, bishops and kings to make two-sided or fully three-dimensional impressions in wax, with a "tag", a piece of ribbon or strip of parchment , running through them.
