PARIS — In countries where live performances have resumed, masked audiences have become a familiar — if still curious — sight. Face coverings for actors are another matter, however: How can performers project their voices and emotions, many theater professionals have asked, with more than half their faces obscured?

The itinerant company Les Tréteaux de France has taken up the challenge — and while performing a 17th-century verse play, no less. Recently in Cergy, a suburb west of Paris, seven masked actors traded alexandrines in Racine’s “Britannicus,” a tragedy charting Roman emperor Nero’s descent into violent lunacy after he abducts the fiancée of Britannicus, his half-brother.

A verse prologue co-written by the cast and the director, Mr Robin Renucci, attempted to explain the unusual costumes. Rome, they said in character before the show started, had been hit by a plague, and masks were a necessity.

The warning felt superfluous; masks are a time-honored theater tradition. The main difference is that the current pandemic requires the mouth to be covered, whereas commedia dell’arte-style half-masks are typically designed to exaggerate the forehead, the eyes and the nose, leaving the mouth unobstructed.

In a phone interview, Mr Renucci, who has been at the helm of Les Tréteaux de France since 2011, said the cast members of “Britannicus” started rehearsing with their new props in May, as soon as the lockdown ended in France.

Acting with a mask is not just a matter of habit.

When a performer speaks a lot onstage, Mr Renucci said, masks become damp and stick to the skin, so each cast member goes through four or five of them in a two-hour performance.

They have experimented with different fabrics: While many wear cotton masks, one actress, Ms Nadine Darmon (who plays Agrippine), switched to polyamide during the run in Cergy, to test the effect on the sound.

Add to that persistent rain in Cergy, where “Britannicus” was performed under a tent at an outdoor activities centre, and during the first few scenes, it took some effort to latch on to the solemn, deliberate rhythm of Racine’s verse.

The actors’ voices sounded muffled, with duller consonants, and several performers were forced to regularly nudge their masks — which slid down their chins with every monologue — back into place.

Yet soon enough, my ear adjusted. We were seated on all four sides of the small stage, and this proximity between cast and audience helped alleviate the muffling effect.

The actors betrayed little discomfort — no small feat considering that breathing in Racine’s plays is tied to the ebb and flow of the alexandrines.

While performers who can speak volumes with their eyes (like Ms Louise Legendre, captivating as Junie, Britannicus’ fiancée) are at an advantage when masked, other details also come to the fore when facial expressiveness is limited.

In Mr Renucci’s contemporary production, Nero and his mother, Agrippine, who wear ostentatious contemporary prints and jewelry, are Italian mafia figures. As Nero, Mr Tariq Bettahar conveyed the emperor’s callousness with purposeful gestures: Scratching his crotch and allowing his hand to rest under his shirt.

In the final minutes of “Britannicus,” Mr Renucci does allow some characters to remove their masks, symbolically, as they come clean about their feelings. I was taken aback to find that several actors suddenly looked very different.

The faces I had mentally sketched in based on their eyes were often wrong, perhaps because their characters colored the audience’s perception of them. Talk about stage illusion; this is an effect we should perhaps get used to in our newly masked lives, too.

The run in Cergy illustrated the uncertainty that is now common for artists. Before “Britannicus” opened, two performances of a new play, Simon Grangeat’s “Faire Forêt (Variations Bartleby),” directed by Ms Solenn Goix, were canceled at the last minute because a performer had developed symptoms consistent with Covid-19.

It turned out to be pharyngitis, but the damage was done. Similar scenarios are likely to play out in other venues in the coming months, as companies adjust to a safety-first approach. THE NEW YORK TIMES