encaustum

Latin encaustum comes from Greek ἔγκαυστον (énkauston), meaning 'burned in,' from en- (in) plus kaiein (to burn). The original reference was to the purple-red ink used by Roman emperors to sign documents — this imperial ink was made using a heated process. But the word attached to all inks, and it entered Old French as enque, which became English 'ink' by the fourteenth century. The word lost its heat but kept its color.

Ink technology is surprisingly diverse. Carbon ink — lampblack (soot) suspended in water with a binding agent — was used in Egypt by 2500 BCE and in China by at least 1200 BCE. Iron gall ink, made from oak galls and iron salts, was the standard European writing ink from the fifth to the nineteenth century. India ink uses carbon black in a shellac binder. Each tradition developed independently, and each produced an ink suited to its local writing surface: papyrus, parchment, paper, silk.

The Dead Sea Scrolls were written in carbon ink. The Magna Carta was written in iron gall ink. The United States Constitution was written in iron gall ink. The ink outlasted the civilizations that made it. Iron gall ink, however, has a fatal flaw: it is acidic and slowly eats through the paper or parchment it sits on. Conservators spend careers stabilizing manuscripts that are being consumed by their own ink. The writing tool is destroying the thing it wrote on.

Digital ink, e-ink, disappearing ink, invisible ink, ink cartridges, tattoo ink, squid ink pasta. The word has become so broadly applied that its original meaning — a dyed liquid for writing — is just one use among many. Printer ink is famously expensive: by volume, it costs more than vintage champagne. The burned-in liquid of the Greek empire has become one of the most consistently overpriced consumer products on earth.