A Slogan From 1947

Rings have marked betrothal for a very long time. Roman betrothals involved a ring, and the ring usually cited as the first recorded diamond engagement ring was given by Archduke Maximilian of Austria to Mary of Burgundy in 1477. None of that is the custom most people now follow, which is that a proposal requires a diamond, preferably a large one, and that its absence needs explaining.

That custom has a start date and an author.

In the 1930s the diamond trade was in trouble. The Depression had collapsed demand, and De Beers, which through its selling organisation controlled most of the world's supply of rough diamonds, needed buyers for a product whose price depended on scarcity being managed. In 1938 it engaged N. W. Ayer, an American advertising agency, to change how Americans thought about diamonds.

The plan, as Edward Jay Epstein later reconstructed it from the agency's own papers, was to attach the diamond to romance so firmly that the size of the stone would be read as the measure of the love. The agency placed stories in magazines, put diamonds on film stars and ran advertisements without a brand name, since the point was not which diamond you bought but that you bought one.

In 1947 a copywriter at the agency, Frances Gerety, wrote the line that went under the advertisements from then on: A Diamond Is Forever. In 1999 Advertising Age named it the slogan of the century.

The line did two jobs.

The first was the obvious one. It joined the stone to permanence and the permanence to marriage. A diamond is the hardest natural material and does not wear out; a marriage is meant to last; the ring makes the one stand for the other.

The second job was quieter and worth more. A diamond that is forever is never sold. That mattered because the price of diamonds rested on controlled supply, and the biggest threat to a controlled price is a secondhand market. Every diamond ever sold is still in somebody's drawer, and if large numbers of people tried to sell them back, new stones would face competition the supplier could not control. A slogan that made selling an engagement diamond feel like a small betrayal kept those stones off the market.

Epstein's 1982 article in The Atlantic took its title from the experience of anyone who tests this: Have You Ever Tried to Sell a Diamond? Jewellers and dealers buy secondhand stones at a steep discount to what the original buyer paid. The diamond is not a store of value in the way the advertising implied. Its retail price includes the margin of everyone in the chain and the cost of the idea.

Then the campaign went abroad, and Japan became the clearest demonstration of how fast a custom can be installed. Japan had no custom of engagement diamonds; betrothal there was marked by an exchange of gifts between families. De Beers began advertising there in the late 1960s, presenting the diamond ring as a sign of modern Western romance. On the figures Epstein reported, fewer than one Japanese bride in twenty received a diamond engagement ring in 1967. By 1981 it was about six in ten.

Fourteen years, from nothing to normal.

There is a modern coda. Laboratory-grown diamonds, physically and chemically the same material as mined ones, have become cheap to make, and they sell for a small fraction of the price of a mined stone. Whether they count is argued about with some heat, and the argument is revealing. If the ring were about the stone, an identical stone would do. That many people feel it does not suggests the ring was always signalling something else: rarity, cost, sacrifice, the two months' salary that a later De Beers campaign named as the proper price of something that lasts forever.

None of this tells you not to buy a diamond. It tells you which parts of the custom are old, which are a campaign and which are your own. The ring is old. The diamond is 1947. The meaning is whatever the two of you decide.