Carbon paper

Patented in 1806 by Englishman Ralph Wedgwood, and in parallel by the Italian Pellegrino Turri, who built an early typewriter for a blind countess. The sheet carries a wax-based pigment; pressure from a pen, typewriter key, or an impact hammer forces the colour down onto the page beneath. Stack several layers and one pass yields several copies.

Impact printers built their whole usefulness on it: a dot-matrix printer fed with multipart forms stamped originals and copies at once, which shipping manifests and receipts demanded. Carbonless NCR paper later took over, embedding microcapsules instead of a loose sheet. The cc in email — "carbon copy" — is the fossil of a technology almost nobody alive has handled.