This article originally appeared on VICE AU.

For nearly a century, skywriting has filled the big blue above with letters of love and persuasion, driven by those with disposable cash and a tendency toward the obvious. But while for us it’s just plumes of fluffy white scripture, the pressure is on for the pilot—there is basically zero margin for error in this business. “Each letter takes about 90 seconds to complete and will only last between three and seven minutes,” explains Cristina Jacuzzi, owner of US skywriting company The Skywriters. “It will be over a mile high, which means that anyone within a 20-mile radius can see it.” The transient nature of the letters combined with the length of time it takes to write them means messages can only be three to six letters long, Jacuzzi says, so you better be concise with your emotions.

The skywriter must also write the message backwards, so it mirrors back correctly to the audience below. It’s so technically precise that for the pilots, it’s not really like writing at all—it’s like acrobatic mathematics. “You’ve got to be good at what you do and know exactly what you’re doing,” Jacuzzi continues. “It’s never an easy task, that’s why there are only six skywriters in the world that can make a living from it.”

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The weather needs to be just right, too. “We need predominantly blue skies,” says Larry Arken, Squadron Commander and Team Flight Lead of New York-based air show team, GEICO Skytypers. “We have a wind limit of 25 knots: anything higher than that and it’ll blow away much faster.” And if you make a mistake? Well, Arken says, you’ve got to start all over again, and hope the blunder fades swiftly into the blue.

Ever since pilots discovered they could, they’ve been writing messages in the sky. It’s thought skywriting began in England after World War I, invented by Major John C. Savage of the Royal Airforce. The first recorded use of skywriting was in May 1922, when Savage and fellow aviator Captain Cyril Turner teamed up to write “Daily Mail” above Epsom Downs racecourse as a paid advertisement for the British paper.

That same year in Times Square, a pilot wrote a phone number in the sky—it was for a hotel, and operators at the establishment were subsequently inundated with over 40,000 calls in three hours. The practice then became an almost immediate sensation: Pepsi, Lucky Strike and Chrysler all took to the skies to sell their products, with the former writing over 2,000 advertisements in the sky in 1940 alone.

Skywriting works by mixing paraffin oil with the heat from the plane’s exhaust. The liquid sits near the engine, around 30 gallons of the stuff, which can write up to around 12 letters. A switch is flipped inside the aircraft, and thick lines of smoke pour out into the sky, perfect and white against the blue. But even in its infancy, people were concerned about the health aspects; in 1923 The New York Times referred to the practice as “celestial vandalism”, envisioning a world so polluted by the plumes that people would be forced to shut their windows indefinitely. These days, Jacuzzi assures, the smoke is biodegradable and non-toxic.

As for the the kind of messages people want to leave hanging in the sky, that rarely changes. “Clients are mostly men,” Jacuzzi says, and the majority are asking for “marriage proposals or to tell their partners they love them.” But there are exceptions to this rule, and many skywriters won’t agree to take on certain messages. These days, for Arken, it’s anything political or religious; for Jacuzzi, it’s provocative gestures, like nude sketches or profanity (“We’ve got young eyes on the ground”).

While there are those who use skywriting as a way to convey their big happy emotions, other message requests are profoundly private or desperately sad. Like those in memory of lost loved ones, or messages loaded with regret. “I once wrote ‘Pooh bear come home’ for a girl who’d left her boyfriend,” Arken remembers. “We never did find out whether she did.”

While skywriting involves just one plane and a constant plume of smoke, skytyping is often considered a more efficient way to get a message into the sky. Created with dashes of the white stuff rather than a consistent stream, each sky-typed letter only takes around four seconds to create—“17 times faster than traditional skywriting,” Arken says. And the message is produced by a fleet of aircrafts.

Skytyping still takes a huge amount of expertise, albeit a slightly different kind: “All skytyper pilots need a background in formation flying,” Arken says, “which is usually learned by military pilots.” Formation flying happens when two or more planes fly in a tight, organised pattern, with one plane designated as the lead. It’s typically used for mutual defence or the concentration of firepower, and, according to Arken, “takes a lot of concentration and precision to hold the planes in a line-abreast formation.”

All of Arken’s team are former military pilots. Five WWII SNJ planes make up his fleet, which were once used in the early 1940s as an advanced military training aircraft, designed to perform all the manoeuvres of a fighter plane but at slower speeds. Flying in a compact formation, the words are generated by a computer in the lead aircraft, which sends radio signals to the other four planes to create what Larry calls “Matrix-style dot lettering”. But despite the speed and efficiency of skytyping, one can’t help but feel the real romance remains in traditional skywriting. Whether that's down to the sweeping curve of the font over the uniform dashes of skytyping, or the fact it's a dying art.