Dated, but still pertinent article.
Have You Ever Tried to Sell a Diamond?
http://www.theatlantic.com/doc/198202/diamond
Thanks for posting the link to this article. Here is an excerpt:
... Specifically, the Ayer study stressed the need to strengthen the association in the public's mind of diamonds with romance. Since "young men buy over 90% of all engagement rings" it would be crucial to inculcate in them the idea that diamonds were a gift of love: the larger and finer the diamond, the greater the expression of love. Similarly, young women had to be encouraged to view diamonds as an integral part of any romantic courtship.
Since the Ayer plan to romanticize diamonds required subtly altering the public's picture of the way a man courts -- and wins -- a woman, the advertising agency strongly suggested exploiting the relatively new medium of motion pictures. Movie idols, the paragons of romance for the mass audience, would be given diamonds to use as their symbols of indestructible love. In addition, the agency suggested offering stories and society photographs to selected magazines and newspapers which would reinforce the link between diamonds and romance. Stories would stress the size of diamonds that celebrities presented to their loved ones, and photographs would conspicuously show the glittering stone on the hand of a well-known woman. ...