In the radiant blue chamber of the ZPrinter 850, a skull is born.

An ink-jet arm moves across a bed of gypsum powder, depositing a layer of liquid that binds the powder together in the shape of a cranial cross-section. Then the arm sweeps across again, brushing on another thin layer of powder, followed by another layer of liquid, indistinguishable from the first, its imprint as abstract as a coffee stain on a napkin. Watching this process is akin to watching a movie with a slide projector—it’s slow. But after 12 hours and 1,500 layers, a technician will reach into the dust and, like the world’s luckiest archaeologist, pull out an impeccably structured replica of a hominid skull.

Meir Kaplan

Since December, the Smithsonian Institution has printed a few dozen such copies. By April 2017, as part of its traveling exhibit Exploring Human Origins, the institution will have presented 95 skulls to participating libraries across the country, an extraordinary diffusion of some of the world’s most precious natural relics (or at any rate, their facsimiles).

The project—the largest 3-D-printing effort yet undertaken by the Smithsonian’s central exhibits team—vividly demonstrates how technology is changing museums’ approach to art and artifacts. As fragile, rare, or ephemeral objects are rendered durable and plentiful, the benefits of accessibility are pitted against those of authenticity.

Jennifer Clark/Smithsonian

The work seen here begins at a Smithsonian vault along the National Mall, where Carolyn Thome, a model maker, uses a scanner to generate a digital 3-D model from a cast of each skull. (The original skulls are owned by foreign museums, and casting additional replicas was not practical. While casting can yield convincing simulacra, it can damage the original.) The rest of the production process takes place at a Smithsonian facility in Maryland, a kind of Santa’s workshop for facsimiles and exhibition scenery. On a recent Friday, in a small room off the main hall, a copy of Thomas Jefferson’s gravestone sat on the floor, and a partially completed 3-D-printed replica of a rattle from Alaska’s Tlingit tribe lay on a table.

After retrieval from the printer, each skull—as brittle as sugar candy, its contours blurred by loose dust—undergoes “depowdering.” Looking a bit like Hamlet with dental tools, Thome brushes the skull clean and blasts it with a high-pressure air jet. Then she applies hot epoxy glue, which permeates the printed powder form, helping to solidify it. Thome used to work in Hollywood, where she created models for use in special effects. “Almost everything I made there got blown up,” she says. “Everything here has to live forever.”

Meir Kaplan

At last, when the epoxy is cured, Thome or one of her colleagues paints the skull with colors mixed to match the original. The result: the one-day-old skull of an Australopithecus africanus from Maryland looks a lot like its 2.3-million-year-old progenitor, a singular specimen reconstructed from a pair of fragments discovered in South Africa in 1947.

In 1936, reflecting on how easily photography could duplicate and disseminate paintings, the German philosopher Walter Benjamin worried that mechanical reproduction threatened to strip history’s glow from artifacts and works of art. “Every day,” he wrote, “the urge grows stronger to get hold of an object at very close range by way of its likeness, its reproduction.” Of course, such reproduction has a proud history of its own. Roman casts provide our only evidence of some Greek statues. Medieval manuscripts survive thanks to diligent copiers. Marcel Duchamp’s ready-made Fountain vanished shortly after it was shown in 1917; the 16 existing versions of the signed, upside-down porcelain urinal are all, ironically, small-batch or bespoke replicas.

Meir Kaplan

Still, the proliferation of replicas does stand to diminish the value of the real thing. The museums that own the original skulls depend on income from visitors and model making, so the Smithsonian will limit production and keep the skulls’ 3-D “blueprints” to itself. Susan Ades, who is in charge of the exhibit’s 3‑D-printing operation, told me that she believes the technology ought to be carefully deployed and fully disclosed in galleries. “For museums,” she said, “the real thing is what we have going. Authenticity.”

Meir Kaplan

Some objects, improbably enough, defend their own authenticity. Because reflective surfaces flummox scanners and cameras, the Smithsonian has so far been unable to duplicate a diorama by the American artist Joseph Cornell or to create a 3-D model of Parliament-Funkadelic’s Mothership. Odd bedfellows, yes, but unprintable both.