In 1938, a De Beers representative wrote to the New York advertising agency N.W. Ayer & Son with a question: could "the use of propaganda in various forms" grow the market for engagement rings?
It needed growing. The diamond engagement ring was not a tradition. Betrothal rings came set with coloured stones, pearls, tiny diamonds, or nothing at all. Frances Gerety, the young copywriter who ended up running the account, later recalled that women of the period would rather the money went on a washing machine or a car. A ring was considered waste.
So Ayer set about manufacturing the custom. It put diamonds on the hands of film stars and fed the stories to newspapers. From 1946 it ran a weekly service supplying 125 papers with notes on which stones which celebrities had been wearing. It sent lecturers into American high schools to talk to teenage girls about engagement rings.
In 1947, working late, Gerety scribbled four words: A Diamond Is Forever. Advertising Age would later vote it the slogan of the twentieth century. It worked because it did two jobs at once — it welded a stone to the idea of permanence, and it quietly discouraged anyone from ever reselling one.
For comparison:
- De Beers hired N.W. Ayer in 1938; the slogan landed in 1947
- US wholesale diamond sales: $23 million in 1939, $2.1 billion by 1979
- De Beers' US advertising budget across the same span: $200,000 to $10 million
- The "two months' salary" guideline was written by the agency, not handed down by custom
Those sales figures are not adjusted for inflation, and the post-war marriage boom did some of the lifting. But the direction is not in dispute: a purchase almost nobody made in 1938 was close to obligatory two generations later.
Frances Gerety wrote the most successful advertising line of the century, spent her career at Ayer, and never married.