Diamonds are not rare and the two months' salary rule was written by an agency

Everything here earned its place by changing an outcome. Nothing about diamond scarcity and engagement spending is included to round the number up.

The campaign that built the convention

In the late 1930s a diamond producer hired an American advertising agency to address weak demand, particularly in the United States. The campaign set out to make the diamond ring an expected part of engagement rather than one option among several. It worked through film placement, magazine features, lectures in schools and a stream of stories about celebrities and their stones.

The now-famous slogan about permanence was written by a copywriter at that agency in the late 1940s. Within a couple of decades the diamond engagement ring had gone from uncommon to close to universal in several countries.

Where the salary rule came from

The guideline that a ring should cost a certain number of months of income was created as advertising copy, not as financial advice. The suggested multiple was revised upwards over the years as campaigns aimed at higher spending, which is not how a genuine norm behaves.

It is a remarkably effective device, because it converts a price question into a question about how much someone cares. Anchoring the purchase to income also means the target rises automatically with prosperity, requiring no further work from the seller. Very few purchases have a socially enforced spending rule attached, and the ones that do usually got it from somebody selling something.

The scarcity question

Gem-quality diamonds are not among the rarer gemstones, and several coloured stones are considerably scarcer in nature. For much of the twentieth century, production from major sources was channelled through a single marketing organisation that regulated how much reached the market. Stockpiling and controlled release kept prices stable and rising, which is a legitimate commercial strategy and not a natural fact about supply.

That arrangement has weakened substantially since, with new producers and new sources selling outside the old channel. Laboratory-grown stones, physically and chemically identical, have added further pressure and now sell at a fraction of mined prices.

What happens when you try to sell one

The gap between retail price and resale value is unusually large, because a new ring's price includes retail margin, marketing and a wide dealer spread. A buyer of second-hand stones is typically a trade buyer who needs to make a margin on resale, so offers reflect wholesale rather than shop prices. Certification, cut quality and size all affect this, and unusual or very high quality stones behave differently from ordinary commercial goods.

Anyone treating a ring as a store of value should check what dealers actually offer before assuming anything about its worth. This is a general information point rather than advice, and anyone with a valuable item should get an independent professional valuation.

Why the campaign was so effective

It attached a product to a life event that occurs once, is emotionally charged, and involves an audience. Purchases of that kind are resistant to price comparison, because shopping around reads as a comment on the relationship. The campaign also promoted the idea that the stone should never be resold, which conveniently removed a second-hand market that would have competed with new sales.

Tested properly, that instruction is the most commercially elegant part of the whole enterprise and is rarely recognised as instruction at all. It is arguably the most successful piece of demand creation in the history of consumer marketing.

Printing a correction has a poor record of taking a myth out of circulation.

What to take from it

None of this means the tradition is worthless, since traditions do not need ancient origins to matter to the people practising them. It does mean the spending rule carries no authority, having been invented by people paid to increase spending. Knowing the origin makes the decision a free one, which is the whole point of tracing where a convention came from.

Where the story actually begins, costs, resale conditions and consumer protections vary widely between countries, so check what applies where you are buying. The most useful question is what you would choose if the guideline had never been written, and now you know that it was written.

Everything above, in order of what to do first

1. The campaign that built the convention. In the late 1930s a diamond producer hired an American advertising agency to address weak demand, particularly in the United States.
2. Where the salary rule came from. The guideline that a ring should cost a certain number of months of income was created as advertising copy, not as financial advice.
3. The scarcity question. Gem-quality diamonds are not among the rarer gemstones, and several coloured stones are considerably scarcer in nature.
4. What happens when you try to sell one. The gap between retail price and resale value is unusually large, because a new ring's price includes retail margin, marketing and a wide dealer spread.
5. Why the campaign was so effective. It attached a product to a life event that occurs once, is emotionally charged, and involves an audience.
6. What to take from it. None of this means the tradition is worthless, since traditions do not need ancient origins to matter to the people practising them.

The takeaway

A copywriter set the price of love in the 1940s, and the invoice is still being honoured.

The satisfying version of a story is the one that travels, which is the whole problem.