High-resolution scan of the 1456 Calixtus Bull, copyright Blaise Agüera y Arcas

Everybody knows what Gutenberg invented…or do we?

History is murkier than we like to think. My novel about the invention of movable type, Gutenberg’s Apprentice, just came out in paperback, but its message doesn’t seem to be sinking in. Gutenberg’s name is still invoked by technologists with astounding regularity. We’re witnessing a transformation of society by computers as profound as the one the Man of the Millennium triggered 560 years ago, everyone agrees. That may be — but the truth is, no one knows what Gutenberg actually invented.

Last autumn printing historians in London took a crack at reverse engineering the world’s first tech startup, hoping to pin it down. (Neither Gutenberg’s press nor any of his metal types survive; the replica workshop at the Gutenberg Museum in Mainz is based on educated guesswork.) Alan May, a British printer and woodworker, went one better, crafting a full-scale wooden handpress based on a 1511 sketch by Albrecht Dürer. Unlike a previous press Mr May built for a BBC documentary featuring Stephen Fry, this one is meant for public study and use. Beyond careful mechanical inferences about how Gutenberg may have repurposed a wine press to pound paper onto inked lead type, its chief virtue, Mr May says, “is that it works.”

But if few dispute the new press’s verisimilitude, the same cannot be said for Gutenberg’s system for casting metal type, the second key element of the invention. A German bibliographer, Christoph Reske of the Johannes Gutenberg University in Mainz, is trying hard to refute a startling theory proposed some years ago at Princeton University by printing historian Paul Needham and physicist Blaise Agüera y Arcas — known to many geeks as the co-developer of Bing maps at Microsoft and now principal scientist at Google.

It’s long been assumed that Gutenberg didn’t just conceive the system of movable type, but also developed a casting device to make each letter from a metal mold. The problem is that this device — the key innovation that turned a laborious technique into mass production — is not documented until the 1470s, many years after production of Gutenberg’s Bible. Back in 2001, meanwhile, the Princeton team discovered so much variation in the shapes of supposedly identical letters in a decree from 1456 that they concluded they couldn’t have been made in the same mold. High-resolution imaging and computational analysis revealed variability far greater than can be explained by differences in inking, pressure and other production processes, Agüera y Arcas explained. Their conclusion shocked the bibliographic world: that Gutenberg hadn’t used a casting device at all, but made his earliest types individually, or a few at a time, in temporary molds of sand or clay.

Reske counters that production variables do explain differences on the printed page; the use of a solid casting mold can’t be excluded. High variability is visible in later types known to have been mass-produced. He visually compared high-resolution scans of a page of the same letters scanned at Princeton and found no significant variation. The human eye is better than a computer at assessing the dimensionality of ink impressed into paper, he maintains. Not so, says Agüera y Arcas, who identified dozens of differently-shaped letter ‘i’s repeating through the 20-page document.

Further research and published data will settle the debate. The more interesting question is whether failure to author this key innovation means Gutenberg should be stripped of the crown of the world’s first tech disruptor. Reske fears this is the case; Agüera y Arcas has no such worries. Gutenberg was a “great, great engineer” whose contributions went far beyond any specific insight, he says. Technological developments result from “a whole series of diagonal moves by a number of people — the idea that a technology emerges fully formed at the beginning is nuts. Anyone who does technology knows that’s not how it works.”

(this article previously appeared in slightly different form in the Financial Times.)