A Diamond Is Forever: De Beers designed a category, and lab-grown stones are testing it

In the late 1930s De Beers, which controlled most of the world’s rough diamond supply, hired the Philadelphia agency N. W. Ayer to sell diamonds in an America still recovering from the Depression. In 1947 an Ayer copywriter, Frances Gerety, wrote the line “A Diamond Is Forever.” It ran in De Beers advertising for decades, and in 1999 Advertising Age named it the slogan of the century. Over the same years the diamond engagement ring went from a habit of the few to an expectation in the United States, then spread to Japan and beyond. The figures usually quoted for that rise come in large part from De Beers’ own research, so we leave them aside, though the direction of the change is well documented.

The pressure arrived from a laboratory. Lab-grown diamonds are physically and chemically the same material as mined ones. In 2018 De Beers launched its own lab-grown brand, Lightbox, at a flat 800 dollars per carat, regardless of size or quality, and positioned it as fashion jewellery rather than as engagement rings. In May 2025 it announced it would close Lightbox, citing a fall of roughly 90% in wholesale lab-grown prices since 2018. Its parent company, Anglo American, has been trying to sell De Beers since 2024; in the summer of 2026 a preferred buyer had been named and the deal was not yet closed.

The ring was the category

Category design says the value game is played in the frame of reference before it is played in the offer, and it works in three moves: frame a point of view, name it, then claim it by occupying the language. De Beers did all of this decades before anyone called it category design. The frame was that love worth marrying for should be marked by something permanent. The name was the engagement ring itself, a ritual with a fixed object at its center. The claim was held for half a century, through advertising that went as far as suggesting how much to spend: in the 1980s, the benchmark offered was two months’ salary.

The trick of the frame is visible in the slogan. “Forever” carries two meanings at once. It speaks of the marriage, and it speaks of the stone, which you keep and pass on. A diamond that is forever is also a diamond that is never sold back, which helped keep second-hand stones off the market and the price of new ones away from what a resale buyer would pay. The story did commercial work that a supply cartel alone could not.

A value that lived in the story

The diamond-water paradox is the oldest question in the economics of value: why is a diamond, which you cannot drink, worth more than water? The answer economists settled on is that we choose at the margin, and the next diamond is scarce. De Beers added a second layer: the next diamond also carried a meaning. The price people paid reflected perceived value, and most of that perception came from the frame around the stone.

Lab-grown diamonds test exactly that layer. When the material can be made at falling cost, the physical scarcity weakens and the story becomes the only part of the value a mined stone can claim. A value that depends on a story holds while the story holds, and stories need maintenance.

Lightbox as a pricing argument

Read as a product, Lightbox was a modest jewellery brand. Read as a pricing move, it was an argument about the category. A single price per carat, set close to cost and indifferent to quality, told the market that lab-grown stones belong to a different frame, closer to fashion than to marriage. De Beers used its own entry into the new category to keep that category small.

The move fit the logic of the original frame. Its limit was that a price signal works only while the rest of the market follows it, and the rest of the market kept cutting. Once a lab-grown stone could be bought for very little, the comparison customers made was the one De Beers had tried to avoid: two stones that look identical, at very different prices, and only a story to explain the gap. Whether the “forever” frame survives that comparison, especially among younger buyers, is still an open question, and the sale of De Beers means a new owner will be the one to answer it.

If part of your margin rests on a story your customers have learned to believe, it pays to know which part, and how you are maintaining it. That is the kind of reading we train your team to do.