Yes, who hasn’t heard that one… and indeed, a diamond can be ‘forever’, provided you don’t hit it at just the right point which makes the stone cleave! But this is not about the science of the stone but its marketing history (marketing in italics).

You may not even realise that there really is an interesting commercial (literally!) story behind it that started just post WW2.
diamonds are forever As ever, it was all about someone coming up with something clever in order to sell more diamonds and here’s the background for all you diamond die-hards… This particular slogan was the basis of an exceedingly clever advertising campaign that began to run in 1948 and that genuinely paved the way for the diamond to become ‘the’ coveted gemstone for engagement rings and generally ‘special moments in life’.

The Phrase Finder website states:
De Beers have used this as a slogan since 1948, and continue to do so (as of 2012). Here’s the announcement of the campaign, from the New York Times’ Advertising News and Notes column, August 1948:

“De Beers Consolidated Mines Ltd., owner of diamond workings in South Africa, plans a fall campaign in leading national magazines which will stress the engagement-ring tradition. Four-colour ads will reproduce paintings by well-known artists and carry the slogan ‘a diamond is forever.’ N.W. Ayer & Sons, Inc., Philadelphia, is the agency.”

The notion wasn’t a new one. In Anita Loos’ book Gentlemen Prefer Blondes, 1925, is the line:
“So I really think that American gentlemen are the best after all, because kissing your hand may make you feel very very good but a diamond and safire bracelet lasts forever.”

And now that you know that, do you look at your lovely diamond engagement ring any differently? I bet not…if you lov’em, then you just do, slogan or no slogan. Right ladies?!

Cateline yellow gold engagement ring