Watchmaking traces its origins to 16th century Europe. And one category of watches present through much of that history — in a discreet, custom-order kind of way — still is being made by several luxury watch brands: timepieces with dials or cases depicting sex.

They are “for the most part, classified just as ‘erotic,’” Simon Bull, a consultant in historical watches, clocks and art based in England, wrote in an email. “Although in French, they have been variously labeled with more subtle titles: polissonne (naughty), libertin (wanton), lubrique (salacious) and scene galante (politely translated as a romantic scene), as well as the more obvious, risqué.”

Another popular name for the genre is saucy; some call it porn. And others have their own ideas.

Miranda Marraccini, the librarian at the Horological Society of New York, wrote in an email that in the 1993 edition of “Hours of Love,” the author Roland Carrera “translates polissonnes as ‘conversation pieces’ and wrote that the French word is ‘a genteel euphemism. Their purpose was to allow a man to entertain a lady in conversation, which might then lead to a meeting of the minds or possibly bodies.’”

But whatever they are called, the major watch brands producing such watches today, including Ulysse Nardin, Blancpain and Richard Mille, say they are doing it to keep the tradition alive.

“We do not produce erotic timepieces because ‘sex sells,’” Jean-Christophe Sabatier, Ulysse Nardin’s chief product officer, wrote in an email. “It is far more complex than that. We produce erotic timepieces in very limited quantities and addressed to a very specific clientele of collectors.”

He also cited the brand’s respect for and desire to perpetuate the “many types of métiers d’art executions, such as engraving, enameling, micropainting, automatons,” which are considered prime elements of the genre.

Erotic images have always been around — think of naked men romping across the pottery of ancient Greece. But according to Nathalie Marielloni, vice curator at the Musée International d’Horlogerie in La Chaux-de-Fonds, Switzerland, the heyday for saucy watches really started with 18th-century pocket watches, thanks to “the beginning of automaton, or little statues that move. Most of the time it’s a man sawing wood or a dog barking, but sometime they are doing erotic scenes.

“We can see this with the Geneva watchmakers and Neuchâtel because they are famous and known for these automatons, especially here in the Jura mountains,” she added. “A century before they had the idea of putting erotic figures on watches, but they weren’t moving. The ability to have moving pieces, the automatons, that’s when the florid erotic flourished.”

Ms. Marraccini noted, “The action of the bodies becomes a kind of active, private pornography.”

The scenes were so risqué, they were hidden. “Throughout their history,” Mr. Bull wrote, “at least until the end of the 20th century, the naughty scene was always wholly or partly hidden within the watch case, which would therefore need to be opened or manipulated in some way to expose it.”

(Since the 17th century there have been watches with covered dials, often called secret watches, and some with protective covers, called hunters in Britain. But Mr. Bull said that neither was the inspiration for or origin of erotic watches. If anything, he wrote in a later email, “the idea for watches to contain erotic scenes would trace its origins to secret scenes hidden inside boxes, small objects or miniature paintings, both European and Near Eastern.”)

In erotic watches, a cover, or cuvette, hid the questionable scene, which could be revealed with the push of a button called, appropriately, the secret. “As a watch was likely carried almost continuously on the person of its owner,” Mr. Bull wrote, “it was an ideal object to provide both a useful function and a means of amusing or even shocking friends with the hidden eroticism.”

The museum in La Chaux-de-Fonds has several examples of such pocket watches, some of which are on display. One of Ms. Marielloni’s favorites was made by Piguet et Meylan in 1820. The case back has an enameled scene depicting Jupiter, in the guise of the goddess Diana, seducing the nymph Callisto. And underneath, revealed to the sound of mechanical music, is an erotic scene of “a monk having intercourse with a young lady,” Ms. Marielloni said. “They seem to be having fun.”

During the 18th century, sex figured in everything from the pastel paintings of Boucher and Fragonard to the purple prose of “Fanny Hill” and the Marquis de Sade. But by the early 19th century, some of the Swiss clergy were outraged by anticlerical depictions on some erotic timepieces and called for them to be banned, while France actually prohibited the making and owning of such watches. But in both countries, few were ever confiscated.

By the Victorian era of the late 19th and early 20th centuries, when chair legs were deemed too suggestive and consequently covered with fringe, erotic watches were still being made by a few independents, but the genre was in danger of turning into a forgotten art.

Ironically, it was the quartz crisis of the 1970s — the rise of inexpensive, battery-operated timepieces that all but decimated the Swiss watch industry — that brought erotic watches back to life. Unable to compete with the low prices of quartz timepieces, large brands chose to elevate their craftsmanship and artistry, the kinds of skills showcased in the genre.

Blancpain has been widely acknowledged as the first major brand to produce a contemporary erotic watch. In 1993, it issued the Villeret Répétition Minutes, a one-of-a-kind wristwatch featuring three naked angels in yellow gold playing music on a background of white gold.

Marc Hayek, Blancpain’s chief executive, said in an email that the timepiece was an exercise to show their watchmakers’ know-how.

“For centuries, the history of watchmaking and that of eroticism have been closely interlinked. This was particularly evidenced by pocket watches with automata, which have long concealed erotic scenes on their case back,” he wrote. “At the beginning of the ’90s, Blancpain brought back to the fore this tradition and became the first horological brand to create minute repeater wristwatches with erotic automata.” (Since then, Blancpain has created other Villeret watches featuring much more explicit sexual activity.)

Denis Flageollet, a master watchmaker, is working on his first erotic timepiece for De Bethune, the brand he co-founded in 2002. It is a two-sided automaton watch with dancers frolicking on one side and making love on the other.

“It’s a fun mechanism to make, polissonne watches are part of the history of watchmaking,” he wrote in an email. “It brings a bit of spice to the workshop when we imagine and make them and it also makes a difference for the collector or the amateur of little pleasures.”

Ulysse Nardin has a long tradition of creating such timepieces, like the Erotica Jarretière, which depicted a couple making love in Venice, and the Classic Voyeur, a scene in a Louis XIV salon.

But the brand said it now was focused on the Classico Manara series, sets of 10 watches depicting a mermaid and a young woman in love. It was introduced in 2019 as a collaboration with the Italian artist and writer Milo Manara, known for his suggestive paintings of beautiful half-clad women.

It took several years of painstaking work to produce the limited edition of 20 sets: 10 sets in stainless steel, now priced at $34,800 each, and 10 sets in 18-karat rose gold, now $44,300 each. The brand said the series was almost sold out.

“The reception has been just incredible,” Mr. Sabatier wrote, adding, “We are preparing something again with Milo Manara.”

The brand also has produced custom work. “We have also created a few unique pieces, at the request of some of our V.V.I.P. clients. Indeed, one of them has been representing a gay couple,” Mr. Sabatier wrote. “It was more than 15 years ago. The request was coming from a person famously known worldwide for his personal collection. Of course as you can understand, I cannot disclose the name of the client and the specifications of the watch as the collection is private.”

Richard Mille took a different tack in 2015 when it created the RM 69 Tourbillon Erotic, a 30-piece limited edition that, according to Ms. Marraccini, the rapper Drake made famous when he wore one to the NBA Finals that year. “It’s an unusual watch because it uses combinations of words, rather than images, to convey an erotic message,” she said.

Each of the watch’s three titanium rollers are engraved with phrases and can be rotated by pressing a button at 10 o’clock: “I lust to caress you madly” and “I want to explore your lips” are among the options.

Much of the Drake coverage pointed out that the watch was priced at $750,000. But, as in the earliest days of personal timepieces, many Swiss watches are status symbols: They are expensive to produce and often are customized, requiring months of work from highly accomplished artisans. Hundreds of years ago, Ms. Marraccini wrote, “aristocratic men used them to demonstrate their wealth and their libertine way of life.” Some things just don’t change.

But one thing that has been changing is society’s perceptions of sexuality. “I think the #MeToo and LGBTQ+ subjects are just too complex to try and relate to what is largely a historic and very limited group of watches,” Mr. Bull wrote. “There are very few, if any, that are exploitative.”

The Swatch Group brand Jaquet Droz is making some erotic automaton watches “to bring back some of the legacy of the brand,” its chief executive, Alain Delamuraz, said in a recent phone interview — although he said it was too early to share any details.

But the watches have “nothing to do with the #MeToo movement,” he said. “As long as there is respect between two people, sexual activity is not forbidden.”