It’s sometimes easy to forget that our technologically complex world wasn’t created out of whole cloth. Or that it wasn’t always here. Without an awareness of the past, “the sense of time falls in upon itself,” writes Lewis Lapham, “collapsing like an accordion into the evangelical present.”

“Vintage Tech,” a column by B. Alexandra Szerlip, will examine some of the under-the-radar stories, personalities and techniques that inform our 21st century lives.

When it comes to revolutionary technologies, it’s hard to top the invention of ink. Book conflagrations (the Mayan codices, the Luftwaffe’s bombing of the British Library, the 2003 bombing of Bagdad’s Grand Library, etc.), assaults against newspapers, and the murder of scholars, publishers and journalists—all speak to its power.

But hand in hand with the evolution of written records has been an evolving counter-technology that both records and conceals—one that has informed everything from innocent diversions and amorous liaisons to espionage and the fate of nations.

Ovid (43 B.C.—A.D. 18), a noted ladies’ man, counseled married women to write illicit love notes in “new milk,” which could be read by adding a touch of coal dust. Roman naturalist Pliny the Elder, who preferred flesh to paper, favored the juice of goat’s lettuce (tithymalus), a medicinal herb, for writing on his lover’s body. Coal dust, redux.

Opponents during the Greco-Persian Wars (499—449 B.C.), adopted a “long game” tactic. The head of an illiterate slave was shaved, his scalp tattooed with secret messages, then the hair was allowed to regrow. Upon arriving at his destination, the head was re-shaved, and read. Technically invisible. Good for one-time use.

Aeneas Tacitus (4th c. B.C.) recommended that, in time of war, a pig’s bladder be inflated and written on with a mix of ink and glue. Once dry, it should be deflated and forced into a glass flask, which was then filled with oil and corked. The recipient had only to pour out the oil and re-inflate the bladder to read the text.

In 1525, Venice’s secret police paid cypher master Marco Raphael the equivalent of a years’ salary to develop new “smart ink” recipes. A few years later, an intriguing volume, credited to Florentine poet-calligrapher G.B. Verini, appeared. A veritable toolkit, it included blank pages requiring the application of charcoal, others calling for lemon juice, plus a bone (for rubbing) and a mirror (for reversed writing). There’s no record that Verini suffered for his efforts, but Giambattista Della Porta wasn’t so lucky. Timing, as they say, is everything.

Della Porta’s Magia Naturalis, an international bestseller, cut a broad swath—from optics, magnetism and meteorology to invisible ink recipes (one called for juices from a dormouse), instructions for an unguent used by...