The office was on the second floor of a shopping centre, above a vape shop and a massage parlour.

I visited at the end of May, only a couple of days before the opening date of the tour, and among Dio’s team, there was a tangible air of anticipation. Dio never became a household name, but he is considered one of the great heavy-metal vocalists of all time, up there with Ozzy Osbourne (whom he replaced in Black Sabbath) and metal-adjacent rockers such as Axl Rose and Robert Plant.

Beginning in the 1970s, Dio took a lead role in codifying a number of his genre’s most ludicrous, yet utterly foundational, conventions. He sang of wolves and demons, toured with an animatronic dragon and supposedly introduced the splay-fingered “devil horns” headbanger’s salute, which he claimed his Italian grandmother used to flash as an old-world method of warding off the malocchio and other forms of bad luck.

Opinion among the Dio faithful, nonetheless, was divided on the subject of his ‘Dio Returns’ comeback tour, largely because Dio has been dead for almost 10 years. The Marina del Rey office suite was the site of a visual-effects company creating a Dio hologram. The hologram would tour with a living backing group consisting, in large part, of former Dio bandmates.

The hologram itself has an uneasy pallor, a brighter shade than the humans onstage but at the same time insubstantial, like a ghost struggling to fully materialise. One crucial decision that had faced the animators was choosing the right age for their creation. Dio in his MTV-era prime tempted them, of course, but then wouldn’t it be strange to watch him perform alongside band members who were roughed up by the ensuing years like the rest of us?

Then again, Dio’s actual age in 2019, were he alive, would be 77, not ideal for a heavy-metal frontman. The creative team settled on a spry, middle-aged Dio, outfitting him in black leather pants, a studded leather wristband, and a bell-sleeved white tunic embossed with a silver cross.

A start-up called Eyellusion produced ‘Dio Returns’. It’s one of a handful of companies looking to mold and ultimately monetise a new, hybrid category of entertainment — part concert, part technology-driven spectacle — centred, thus far, on the holographic afterlives of deceased musical stars. Eyellusion also toured a hologram of Frank Zappa in the spring, in a show overseen by Zappa’s son, Ahmet. The tour kicked off in April at the Capitol Theatre in Port Chester, New York, about an hour north of Manhattan in Westchester County.

A few hours before the show, I talked to the owner of the venue, the 47-year-old concert promoter Peter Shapiro. Shapiro, who attended a preview of the Zappa concert, said: “What I just saw felt closer to seeing Zappa than seeing a cover band do it.”

Based on ticket sales alone, he would definitely book another hologram show, he added. The theatre, which holds 1,800 people, was close to sold out for opening night.

“But here’s the headline,” Shapiro went on. “Look at who’s gone, just in the last couple of years: Bowie, Prince, Petty. Now look who’s still going but who’s not going to be here in 10 years, probably, at least not touring: The Stones, the Who, the Eagles, Aerosmith, Billy Joel, Elton John, McCartney, Springsteen.

That is the base not just of classic rock but of the live-music touring business. Yes, there’s Taylor Swift, there’s Ariana Grande. But the base is these guys.

Shapiro’s calculation might be morbid, but he isn’t wrong. According to the trade publication Pollstar, roughly half of the 20 top-grossing North American touring acts of 2019 were led by artists who were at least 60 years old, among them Cher, Kiss, Fleetwood Mac, Paul McCartney, Dead & Company and Billy Joel. The Rolling Stones, Elton John, and Bob Seger took the top three slots.

Using technology to blur the line between the quick and the dead tends to be a recipe for dystopian science fiction, but, in this case, it could also mean a lucrative new income stream for a music industry in flux, at a time when beloved entertainers can no longer count on CD or download revenues to support their loved ones after they’ve died.

Tupac Shakur became one of the earliest test subjects for the new technology 15 years after his murder, when his hologram made a surprise appearance at the 2012 Coachella festival.

To actually project a person-size holographic image into three-dimensional space, à la Princess Leia in Star Wars: A New Hope, would require powerful, prohibitively expensive lasers that would also burn human flesh. The Tupac hologram was created with a combination of CGI, a body double, and a 19th-century theatrical trick known as Pepper’s Ghost, some variation of which has been used for almost all the hologram musical performances of recent years.

Marty Tudor, chief executive of Base Hologram Productions, is an entertainment-industry veteran whose multifarious career has included, among other things, managing Paula Abdul and Jon Cryer, producing a series of exercise videos with a trainer from The Biggest Loser and running an independent record label. When he saw footage of the Tupac hologram at Coachella, Tudor had a hunch that there might be potential for the new technology beyond gimmicky festival cameos.

Tudor took the idea to Brian Becker, the former chief executive of Clear Channel Entertainment, which was the largest events promoter and venue operator in the country during Becker’s tenure.

“We’re always cognisant of seams in our industry that might allow us to do things differently,” Becker said. After hearing out Tudor’s hologram pitch, Becker wondered if the technology might represent such a seam.

In the wake of the Tupac hologram, a somewhat motley assortment of newly minted hologram companies were asking themselves the same question, and soon a scramble to lock down exclusive deals with music estates ensued. Digital Domain, the visual-effects house that resurrected Tupac, wound up declaring bankruptcy not long after the Coachella performance, but one of its owners, a Florida investor named John Textor, quickly started a new company, Pulse Evolution, which produced the Jackson hologram and soon after announced that it had also cut hologram deals with the estates of Elvis Presley and Marilyn Monroe, as well as for the band Abba, which broke up in 1982.

Base Hologram, founded by Tudor and Becker, started out by securing rights to produce holograms of Maria Callas and Roy Orbison, debuting each show in 2018 with performances in Europe and America.

In February, Base will unveil the dead-celebrity-hologram sector’s biggest marquee name thus far, at least for a full concert: Whitney Houston, whose tragic, relatively recent death has made the planned tour the most controversial of any on the books. (Shortly after the announcement, rapper Questlove tweeted: “& hell begins.”) Deborah Speer, a features editor at Pollstar, which covers the live-entertainment industry, told me that based on the numbers she has seen for the Orbison and Zappa tours, “obviously, there’s a market” for hologram shows. According to the trade publication, the solo Orbison tour grossed nearly $1.7m over 16 shows, selling 71% of the seats available, while Zappa sold an average of 973 seats per show, nearly selling out venues in Amsterdam and London.

Whether such tours can cross from clubs, theatres, and performing-arts centres into arenas remains to be seen and will depend largely on the success of bigger-name late stars such as Houston.

Early one morning in May, I visited a soundstage in the Griffith Park neighborhood of Los Angeles to observe a motion-capture shoot for the Whitney Houston hologram. Fatima Robinson, the director of the production, wore a head scarf and a winter jacket and cupped a rechargeable electronic hand-warming device between her palms.

Robinson is a choreographer whose credits include Kendrick Lamar’s 2016 Grammys performance, the Weeknd’s 2016 Oscars performance, the film version of Dreamgirls, NBC’s live broadcast of The Wiz, and music videos for Michael Jackson, Mary J Blige and Aaliyah. She also choreographed the living Houston herself in 1993, for the ‘I’m Every Woman’ video.

“She was pregnant at the time and in a wonderful place,” said Robinson.

Veterans of pedigreed Hollywood post-production houses create the CGI holograms in the same way they would make film characters such as Gollum or Thanos: Motion-capture photography records the performance of a body double, which becomes the basis for a three-dimensional digital model, a block of clay animators proceed to modify — in the case of celebrity holograms, most drastically by augmenting the body double’s features with a digitally sculpted likeness of the artist, which can lip-synch to an existing vocal track.

The Houston body double took the stage and began to run through the moves for the first song of the day, ‘Step by Step’, a jaunty, affirmational gospel-dance track from the 1996 soundtrack to The Preacher’s Wife. The double had freckles and wore her hair in dyed cornrows but possessed Houston’s approximate build.

She wore black tights, a black T-shirt, and a baggy white cardigan and stood atop a sort of oversize lazy susan, which crouching tech guys, who referred to the device as a turntable, slowly spun as she lip-synched to the song.

There was something eerie about the way Houston’s voice and the mid-’90s dance beat echoed through the vast space — music being played at club volume to a nearly empty room, with no one dancing, not even the avatar pretending to sing. But despite the workaday setting and the unconcealed artifice, by the third or fourth time I heard the song, I couldn’t help feeling ... something.

In the final show, Tudor whispered to me, the turntable could be digitally removed or made to look like something else. The creative team hadn’t settled on anything yet. But if they wanted to, they could make Houston look as if she were floating on air, spinning, ascendant.

I sat in Marina del Rey in the office of Eyellusion’s creative director, Chad Finnerty, as he digitally manipulated a photorealistic 3-D image of Ronnie James Dio’s face. Finnerty grew up in Pennsylvania with dreams of becoming a Disney animator — old-fashioned cell animation, like what they did on Snow White and the Seven Dwarfs — but by the time he graduated from college, the world had gone digital.

He spent years working as a CGI animator, and when Jeff Pezzuti, a Westchester-based vice president of finance at a cloud-computing consulting firm, decided to start his own hologram company, Eyellusion, he reached out to Finnerty, asking if he wanted to talk. Pezzuti loved heavy metal — he wore a Dio T-shirt for his seventh-grade class picture — and after seeing the Tupac hologram, he wondered:

Can we do something like that in the rock world?

Eyellusion has since received a $2m investment from Thomas Dolan, whose family owns controlling interests in Madison Square Garden and AMC Networks and whose father founded the New York-area cable-television giant Cablevision.

Finnerty supervised the creation of the Zappa and Dio holograms for Eyellusion.

“I’m a bit rusty with this programme,” he apologised, pecking at his desktop keyboard. Soon a hideously lifelike digital rendering of Dio’s face appeared on a large-screen monitor hanging on the wall.

“We collected all of our data in 2017,” Finnerty explained. That’s when they filmed the body double and did the facial capture, is what he meant. During the facial capture, hundreds of eye, mouth, and facial-muscle movements of a living subject (not necessarily the body double) are recorded. Imagine a puppeteer, Finnerty said, only with thousands of puppet strings to manipulate.

He clicked his mouse, manipulating a digital lever on the screen, and Dio’s eye suddenly, eerily shifted to the left. You couldn’t do this two years ago, Finnerty went on, moving another lever. Dio’s eyes shifted right, up, down.

As for concerts, in the not very distant future, Finnerty predicted, the technology would evolve to the point at which a puppeteer sitting in the wings with a laptop could work the digital strings live — allowing the hologram to react to the crowd or to members of a live band.

Whenever I wondered aloud whether fans might find the shows unsettling or disrespectful, the hologram-industry representative I happened to be speaking to would grow defensive. It’s stagecraft, part of a larger production, the person would tell me. We respect these artists, and we take what we’re doing very seriously.

And, as these representatives point out, people see tribute acts all the time. An Australian Pink Floyd, Tudor said, just played in Los Angeles. Pollstar’s Speer told me that well over 175 tribute bands reported numbers to the magazine; one of the better performers, Rain — a Tribute to the Beatles, often turns up in the top half of the Concert Pulse chart, averaging 1,833 tickets and $95,955 per show over the past three years.

For what it’s worth, the crowd at the Zappa concert seemed utterly charmed — cheering when hologram Zappa materialised in the centre of the stage during the opening number, ‘Cosmik Debris’.

I was sitting about eight rows from the front. It looked like Zappa up there, more or less, though his form radiated the paranormal brightness that holograms can’t help emitting. Eventually, ‘Zappa’ addressed the audience:

Good evening. You won’t believe it, but I’m as happy to see you guys as you are to see the show. I’m your resident buffoon, and my name is Frank.

Before the concert, Ahmet Zappa had pointed me to a passage in his father’s 1989 autobiography in which he seemed to predict the technology that would allow him to return to Port Chester 26 years after his death: A digressive riff about his “idea for a new device, potentially worth several billion dollars”, one that would “generate free-standing 3-d images, in any size (on your coffee table at home, or on a larger scale for theatrical use)”.

So maybe Zappa would have appreciated his 2019 tour. And maybe holograms will make the leap from ridiculous-seeming technology to ubiquity, like podcasts or e-cigarettes.

Ahmet was 15 when his father received a diagnosis of prostate cancer and was given three months to live. One way to think about the show, he told me, is as “a very childlike way of dealing with loss”. For a couple of hours every night, Frank is up there onstage again, playing with his guys, and Ahmet can almost convince himself that he has his father back.

You’d think there would be a market for something like that.

- Adapted from an article that originally appeared in The New York Times Magazine.