Kermes is a red dye derived from the dried bodies of the females of a scale insect in the genus Kermes, primarily Kermes vermilio. The Kermes insects are native in the Mediterranean region and live on the sap of the Kermes oak. They were used as a red dye by the ancient Greeks and Romans. The kermes dye is a rich red. It has good colour fastness in silk and wool. It was much esteemed in the medieval era for dyeing silk and wool, particularly scarlet cloth. Post-medievally it was replaced by other red dyes, starting with cochineal.

Kermes dye is of ancient origin; jars of kermes have been found in a Neolithic cave-burial at Adaouste, northeast of Aix-en-Provence.

In the Middle Ages, rich crimson and scarlet silks dyed with kermes in the new silk-weaving centers of Italy and Sicily exceeded the legendary Tyrian purple "in status and desirability". The dyestuff was called "grain" in all Western European languages because the desiccated eggs resembled fine grains of wheat or sand, and textiles dyed with kermes were described as dyed in the grain. Woollens were frequently dyed blue with woad before spinning and weaving, and then piece-dyed in kermes, producing a wide range colours from blacks and grays through browns, murreys, purples, and sanguines. By the 14th and early 15th century, brilliant full grain pure kermes scarlet was "by far the most esteemed, most regal" colour for luxury woollen textiles in the Low Countries, England, France, Spain and Italy.

Following the Spanish conquest of the Aztec Empire, Mexican cochineal, which produced a stronger dye and could thus be used in smaller quantities, replaced kermes dyes in general use in Europe.

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