The ink of the Sepia officinalis
The dark, semitransparent, reddish-brown ink known as sepia, comes from the pouch of the Sepia officinalis (cuttlefish). Sepia is mostly comprised of melanin, which creates its color, as well as mucus, which imparts a glutinous texture. To this liquid a medium is added—usually gum arabic and water. It can vary greatly in tone depending on the concentration of the solution and is very easily faded in sunlight. The ink is known to have been in use since the 17th century and became common in the 19th century. Now, the term “sepia” refers to any brown ink with a reddish tone, regardless of its origin.
Images above are courtesy of cienciayculturaescrita.es & fao.org