The Diamond Engagement Ring Was Invented by a Copywriter in 1947

In 1938, De Beers had a problem. It had too many diamonds.

The company controlled between 80 and 90 percent of the world's diamond supply. It had access to enormous reserves in South Africa. Demand had collapsed in the Depression. And diamonds, contrary to the entire mythology that would later be built around them, are not particularly rare.

So De Beers hired an advertising agency in Philadelphia called N. W. Ayer & Son and gave it an assignment that had never been attempted at that scale.

Not to sell more diamonds. To make people believe they needed one.

In 1940, roughly ten percent of first-time brides in America received a diamond engagement ring. By 1990, that figure was around eighty percent.

Nothing changed about diamonds in those fifty years. No new property was discovered. No shortage occurred. What changed was a story, written by an advertising agency, on behalf of a company that owned the supply.

De Beers sales went from $23 million in 1939 to $2.1 billion by 1979.

And in July 2026, Anglo American agreed to sell De Beers for approximately one billion dollars. The same business was valued at over eighteen billion in 2001.

Here is the full file.

N. W. Ayer did not run a normal advertising campaign. It ran a cultural engineering programme, and the tactics are worth listing because they explain how belief actually gets built.

The agency placed diamonds on Hollywood actresses and fed diamond storylines to screenwriters, so that audiences would see the stone at emotional peaks in films rather than in advertisements.

It planted stories in newspapers and magazines linking diamonds to romance, in editorial pages rather than ad space, because a story reads as truth and an advertisement reads as a pitch.

And it sent lecturers into American high schools to teach young women about the tradition of the diamond engagement ring.

Read that last one again. Lecturers were dispatched to classrooms to describe as an ancient custom a practice that the same agency had invented in the preceding few years.

Within three years of the campaign starting, diamond sales in the United States rose by about fifty percent.

Then, in 1947, a copywriter at the agency named Frances Gerety wrote four words at the bottom of an advertisement, late at night, and reportedly was not impressed with them.

A diamond is forever.

Advertising Age would later name it the greatest advertising slogan of the twentieth century. Here is why it deserved that, and it has almost nothing to do with romance.

The line did three jobs simultaneously, and only the first is obvious.

It attached the stone to eternal love, which made it emotionally necessary.

It made the purchase a one-time, must-buy event rather than a discretionary luxury.

And it killed the resale market.

That third function is the one that matters commercially, and it is the reason this is a finance story rather than a marketing story.

A diamond you keep forever is a diamond that never comes back onto the market. If the eighty percent of American brides who received a diamond between 1950 and 1990 had resold those stones, there would now be an enormous secondary supply of used diamonds competing directly with De Beers' new production, at prices De Beers did not control.

The slogan prevented that. It made resale feel like a betrayal of the sentiment rather than a financial decision. Generations of diamonds went into drawers and safes and stayed there.

Which is why the single most useful fact about diamonds is the one almost nobody learns until they try it: take a diamond engagement ring to be sold, and you will typically be offered a fraction of what was paid for it. Frequently a small fraction.

That is not a scam by the buyer. It is the honest market price of an object whose retail value was constructed, and whose resale value was deliberately never allowed to develop.

Then there is the number, which is the purest example in this entire newsletter of a fact that everyone believes and nobody can source.

In the 1930s and 1940s, De Beers advertising suggested a man should spend one month's salary on an engagement ring.

By the 1980s, the advertising said two months. One campaign asked how else two months' salary could last forever.

In Japan, where De Beers ran a separate campaign that took the country from almost no diamond engagement rings in the 1960s to a majority of brides within two decades, the figure promoted was three months.

There is no traditional basis for any of these numbers. There is no historical custom behind them. They were marketing decisions, adjusted upward over time, and calibrated differently by market.

The mechanism is elegant. By expressing the price as a proportion of income rather than a fixed sum, the rule scales automatically. It never prices anyone out and it never leaves money on the table. And it converts a purchase decision into a test of devotion, which is a category of decision where people do not comparison shop.

Millions of people have made the largest discretionary purchase of their young adult lives against a benchmark invented by an advertising agency to sell surplus inventory.

Every constructed value holds until someone tests it. The diamond story survived for eighty years. It is being tested right now, and the results are arriving faster than anyone expected.

Laboratory-grown diamonds are not imitations. They are not cubic zirconia. They are chemically, physically, and optically identical to mined diamonds, produced by replicating the pressure and temperature conditions of the earth's mantle, or by growing crystals from carbon vapour. A trained gemologist cannot distinguish them without specialised equipment.

Over the past five years, lab-grown diamond prices have fallen by an estimated 80 to 90 percent as production scaled. They now account for roughly half the market by some measures.

Here is what that did to the company that built the industry.

Anglo American, which owns 85 percent of De Beers, has written down its value by billions across three consecutive years. In the first half of 2026, De Beers' average realised price fell to $105 per carat, down 32 percent from $155 a year earlier. Revenue fell 19 percent. The company posted an underlying loss. It announced a two-year production halt at its Venetia mine in South Africa.

De Beers had launched its own lab-grown brand, Lightbox, deliberately pricing synthetic stones low to position them as costume jewellery and protect the mined product. It closed the brand.

In July 2026, Anglo American identified a preferred bidder. Reported transaction value: approximately one billion dollars, structured with a deferred component and an earnout.

When Anglo American and the Oppenheimer family took De Beers private in 2001, the implied valuation exceeded eighteen billion dollars.

The company that spent a century manufacturing the belief that a diamond's value was permanent is being sold for around one twentieth of its former worth, because someone produced a chemically identical stone and the belief did not survive the comparison.

Three conclusions.

Scarcity is frequently a decision rather than a fact. De Beers did not sell rare stones. It sold common stones and controlled the supply so completely that they behaved as though they were rare, then spent enormous sums teaching the public that the rarity was natural. This is not unique to diamonds. Ask, of any expensive thing, whether the scarcity is geological, technical, or administrative. Geological scarcity is real and durable. Administrative scarcity is a policy, and policies can change, sometimes overnight, sometimes because a laboratory in China figured out how to make the thing.

Price and resale value are two different numbers, and the gap is where the story lives. A diamond's retail price and its resale price have diverged by a large margin for eighty years, and that gap is the exact measure of how much of the price was narrative rather than substance. This is the single most useful test you can apply to any asset. Not what does it cost, but what will someone else pay me for it tomorrow, and why. Anything where those two numbers are far apart is holding a story in the difference, and stories can end.

Constructed value can survive for a century and then collapse in five years. This is the part people underestimate. The diamond narrative held from 1938 to roughly 2020. Eighty years of stability, generation after generation, a tradition so established that lecturers were sent to schools to explain it. And then a manufacturing process improved, the price of the substitute fell 80 percent, and an eighteen billion dollar company became a one billion dollar company. Duration is not evidence of durability. A story that has held for a very long time is not therefore true; it is simply a story that has not yet been tested by something that could break it.

10%. The share of American first-time brides receiving a diamond engagement ring in 1940.

80%. The share in 1990.

Nothing about diamonds changed between those two dates. An advertising agency changed what people believed, and a company that owned the supply collected the difference for fifty years.

In July 2026, that company was put up for sale for approximately one billion dollars, down from more than eighteen billion, because a chemically identical stone can now be produced in a factory and the story stopped working.

The stone was always just carbon. The price was the story.

That is not a conspiracy theory. That is the balance sheet.

The Dark Money Letter is published every Wednesday. → thedarkmoneyletter.com

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