When I decided to propose to the woman who is now my wife, I gave a lot of thought to how I was going to do it. But I didn't think much about what I was going to do it with. Not only did a diamond ring seem the logical—nay, the inevitable—choice, but I had just the very diamond. My grandfather had scrounged up enough money to buy a diamond ring for my grandmother in the early 1950s, and the stone had passed to me when he passed away. I reset the diamond in a more modern band, got the ring appraised, and slipped it on my fiancée's finger.

It was a beautiful moment—a gesture of love and commitment spanning generations. And it was also exactly what De Beers Consolidated Mines, Ltd. wanted. I was a century-old marketing campaign, actualized. And I'm far from alone; three-quarters of American brides wear a diamond engagement ring, which now costs an average of $4,000.

Every so often, an article comes along that makes you thoroughly rethink a rote practice. Edward Jay Epstein's "Have You Ever Tried to Sell a Diamond?" was one of them. In his 1982 Atlantic story, the investigative journalist deconstructed what he termed the "diamond invention"—the "creation of the idea that diamonds are rare and valuable, and are essential signs of esteem."

That invention is surprisingly recent: Epstein traces its origins to the discovery of massive diamond mines in South Africa in the late 19th century, which for the first time flooded world markets with diamonds. The British businessmen operating the South African mines recognized that only by maintaining the fiction that diamonds were scarce and inherently valuable could they protect their investments and buoy diamond prices. They did so by launching a South Africa–based cartel, De Beers Consolidated Mines, Ltd. (now De Beers), in 1888, and meticulously extending the company's control over all facets of the diamond trade in the ensuing decades.

Most remarkably, De Beers manipulated not just supply but demand. In 1938, amid the ravages of the Depression and the rumblings of war, Harry Oppenheimer, the De Beers founder's son, recruited the New York–based ad agency N.W. Ayer to burnish the image of diamonds in the United States, where the practice of giving diamond engagement rings had been unevenly gaining traction for years, but where the diamonds sold were increasingly small and low-quality.

Meanwhile, the price of diamonds was falling around the world. The folks at Ayer set out to persuade young men that diamonds (and only diamonds) were synonymous with romance, and that the measure of a man's love (and even his personal and professional success) was directly proportional to the size and quality of the diamond he purchased. Young women, in turn, had to be convinced that courtship concluded, invariably, in a diamond.

Ayer insinuated these messages into the nooks and crannies of popular culture. It marketed an idea, not a diamond or brand:

Movie idols, the paragons of romance for the mass audience, would be given diamonds to use as their symbols of indestructible love. In addition, the agency suggested offering stories and society photographs to selected magazines and newspapers which would reinforce the link between diamonds and romance. Stories would stress the size of diamonds that celebrities presented to their loved ones, and photographs would conspicuously show the glittering stone on the hand of a well-known woman. Fashion designers would talk on radio programs about the "trend towards diamonds" that Ayer planned to start. ...

In its 1947 strategy plan, the advertising agency ... outlined a subtle program that included arranging for lecturers to visit high schools across the country. "All of these lectures revolve around the diamond engagement ring, and are reaching thousands of girls in their assemblies, classes and informal meetings in our leading educational institutions," the agency explained in a memorandum to De Beers. The agency had organized, in 1946, a weekly service called "Hollywood Personalities," which provided 125 leading newspapers with descriptions of the diamonds worn by movie stars. ... In 1947, the agency commissioned a series of portraits of "engaged socialites." The idea was to create prestigious "role models" for the poorer middle-class wage-earners. The advertising agency explained, in its 1948 strategy paper, "We spread the word of diamonds worn by stars of screen and stage, by wives and daughters of political leaders, by any woman who can make the grocer's wife and the mechanic's sweetheart say 'I wish I had what she has.'"

In the late 1940s, just before my grandfather started hunting for his diamond ring, an Ayer copywriter conceived of the slogan that De Beers has used ever since: "A Diamond Is Forever." "Even though diamonds can in fact be shattered, chipped, discolored, or incinerated to ash, the concept of eternity perfectly captured the magical qualities that the advertising agency wanted to attribute to diamonds," Epstein writes. A diamond that's forever promises endless romance and companionship. But a forever diamond is also one that's not resold. Resold diamonds (and it's maddeningly hard to resell them, as Epstein's article details) cause fluctuations in diamond prices, which undermine public confidence in the intrinsic value of diamonds. Diamonds that are stowed away in safe-deposit boxes, or bequeathed to grandchildren, don't.

Between 1939 and 1979, De Beers's wholesale diamond sales in the United States increased from $23 million to $2.1 billion. Over those four decades, the company's ad budget soared from $200,000 to $10 million a year.

A 1960 De Beers ad in Reader's Digest (SensaiAlan/Flickr)

De Beers and its marketers proved extraordinarily adaptable at molding public perceptions. When the U.S. engagement marked seemed tapped out, a new campaign promoted the gift of a second diamond as a way to reaffirm romance later in marriage. When small Soviet diamonds entered the market, people were told that the size of diamonds (as opposed to their quality, color, and cut, or the mere gesture of buying a diamond in the first place) didn't matter much after all. (Some gambits backfired, like the diamond-ring-for-men misadventure of the 1980s.)

And when De Beers sought to expand internationally in the mid-1960s, it didn't flinch at entering markets like Japan's, where a deeply rooted tradition of arranged marriages left little space for premarital romance, let alone diamond engagement rings. De Beers, Epstein writes, aggressively marketed diamond rings in Japan as tokens of "modern Western values." In 1967, when the campaign began, less than 5 percent of betrothed Japanese women had a diamond engagement ring. By 1981, that figure had risen to 60 percent, and Japan had become the second-largest market, after the United States, for diamond engagement rings. De Beers conjured up "a billion-dollar-a-year diamond market in Japan, where matrimonial custom had survived feudal revolutions, world wars, industrialization, and even the American occupation," Epstein marvels.

De Beers had far more success in Japan than it did in other countries like Brazil, where both women and men typically wear a simple band on their right hand while engaged and switch the ring to their left hand once married. But the social transformation that took place in Japan in the 1970s may be repeating itself today in China, where, according to a recent Citigroup report (which relies on De Beers data), more than 30 percent of Chinese brides now receive diamond engagement rings. The practice barely existed in the country in the 1990s.

Percent of First-Time Brides Who Receive Diamond Engagement Rings

Citigroup/De Beers

A 2014 report by Bain & Company similarly noted that China, India, and the United States will drive the majority of growth in diamond-jewelry consumption over the next decade, in part because of growing interest in diamond engagement rings in India and China, and stable interest in the U.S.

A Forecast of Rough-Diamond Demand Growth Through 2024

Bain & Company

De Beers is still a major player in the diamond industry, though it's not as dominant as it once was. The copywriter behind "A Diamond Is Forever" passed away in 1999, and N.W. Ayer ceased operations three years later. But the Diamond Invention lives on.