What is function of a seal?

Answer 1

A cylinder seal is a cylinder engraved with a 'picture story', used in ancient times to roll an impression onto a two-dimensional surface, generally wet clay. Cylinder seals were invented around 3500 bc in the Near East, at the contemporary site of Susa in south-western Iran and at the early site of Uruk in southern Mesopotamia. They are linked to the invention of the latter cuneiform (first form of writing) writing on clay cylinders. They were used as administrative tool, jewellery and as magical amulets, later versions would employ notations with Mesopotamian hieroglyphs. In later periods, they were used to notarize or attest to multiple impressions of clay documents. Also Graves and other sites hoarding precious items such as gold, silver, beads, and gemstones often included one or two cylinder seals, as honorific grave goods.

The seal itself was made from hard stone, glass, or ceramics such as Egyptian faience. Many varieties of material such as hematite, obsidian, steatite, amethyst and carnelian were used to make cylinder seals, but lapis lazuli was especially popular because of the beauty of the blue stone and as The alluvial country of Mesopotamia lacks good stone for carving; hence the large stones of early cylinders were imported probably from Iran.[4]

While most Mesopotamian cylinder seals form an image through the use of depressions in the cylinder surface (see lead photo above), some cylinder seals print images using raised areas on the cylinder (see San Andrés image below). The former are used primarily on wet clays; the latter, sometimes referred to as roller stamps, are used to print images on cloth and other similar two dimensional surfaces.

Cylinder seals are a form of impression seal, a category which includes the stamp seal and finger ring seal.