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Ask Dr. Knowledge

Can I write with squid ink?

March 22, 2010

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What is squid ink? I eat it in black pasta and risotto dishes, but is it safe? Could you write with it?

Most cephalopods — a family of mollusks that includes squid, octopus, and cuttlefish — produce a dark pigment, often referred to as ink, as a defense mechanism to cover their escape when threatened.

The inks’ colors differ slightly, depending on the organism, with the ink of octopuses being the blackest. Squid produce bluish-black ink, and cuttlefish ink is reddish brown.

These inks have fairly complex compositions, but the color is mostly due to melanins — the same class of pigments responsible for the colors of human hair and skin.

Eumelanin is brown-black, while pheomelanin is reddish-brown. The detailed composition of any given ink depends on the species.

While squid and octopus ink can be used in cooking, many of the most famous dishes, such as risotto al nero di seppia (risotto with black ink from cuttlefish), use cuttlefish ink. There is no reason to worry about eating these inks, unless you have an allergy to them. They’re delicious.

You could certainly use them for writing, though it isn’t done much nowadays. The brownish ink of the cuttlefish, dried and mixed with shellac (to make it water-resistant), enjoyed great popularity in the 19th century for writing and drawing — it was called sepia. The word comes from the Latin for cuttlefish.

The term sepia also refers to a sort of coloring sometimes done to black-and-white photographs to soften the blacks to brown, by reacting sulfur with the silver in the images, making them more the color of old sepia drawings.

In addition to making the pictures seem warmer, it improves their stability against aging. The term sepia here refers to color, though, not to the use of cuttlefish ink.

Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.