Here's the deal.

Yes, diamond ring existed before De Beers' ad campaign. They declined after WWI and especially during the Great Depression, and engagement rings were starting to go out of style, period.

De Beers changed that.

In 1939 only 10% of engagement rings had diamonds. By 1990, 80% did, in the United States. I am guessing the non-diamond ones are plain bands.

When someone I knew got engaged, the first question an acquaintance asked was "what carat diamond is it?" it was so insulting of a question I was disgusted.

When female friends of mine get engaged, they go "let me show you the ring."

By the way I refuse to own or wear either a engagement ring or a wedding ring. (I'm a lady - fyi)

http://books.google.com/books?id=SpPUrOhQ7I4C&pg=PA327#v=one...

http://books.google.com/books?id=s1Oa5Fqy0dUC&pg=PA49#v=onep...

Here's a long article a read a long time ago...

http://www.theatlantic.com/magazine/archive/1982/02/have-you...

Here's the key part:

In Europe, where diamond prices had collapsed during the Depression, there seemed little possibility of restoring public confidence in diamonds. In Germany, Austria, Italy, and Spain, the notion of giving a diamond ring to commemorate an engagement had never taken hold. In England and France, diamonds were still presumed to be jewels for aristocrats rather than the masses. Furthermore, Europe was on the verge of war, and there seemed little possibility of expanding diamond sales. This left the United States as the only real market for De Beers's diamonds. In fact, in 1938 some three quarters of all the cartel's diamonds were sold for engagement rings in the United States. Most of these stones, however, were smaller and of poorer quality than those bought in Europe, and had an average price of $80 apiece. Oppenheimer and the bankers believed that an advertising campaign could persuade Americans to buy more expensive diamonds.

Oppenheimer suggested to Lauck that his agency prepare a plan for creating a new image for diamonds among Americans. He assured Lauck that De Beers had not called on any other American advertising agency with this proposal, and that if the plan met with his father's approval, N. W. Ayer would be the exclusive agents for the placement of newspaper and radio advertisements in the United States. Oppenheimer agreed to underwrite the costs of the research necessary for developing the campaign. Lauck instantly accepted the offer.

In their subsequent investigation of the American diamond market, the staff of N. W. Ayer found that since the end of World War I, in 1919, the total amount of diamonds sold in America, measured in carats, had declined by 50 percent; at the same time, the quality of the diamonds, measured in dollar value, had declined by nearly 100 percent. An Ayer memo concluded that the depressed state of the market for diamonds was "the result of the economy, changes in social attitudes and the promotion of competitive luxuries."

Although it could do little about the state of the economy, N. W. Ayer suggested that through a well-orchestrated advertising and public-relations campaign it could have a significant impact on the "social attitudes of the public at large and thereby channel American spending toward larger and more expensive diamonds instead of "competitive luxuries." 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. Fashion designers would talk on radio programs about the "trend towards diamonds" that Ayer planned to start. The Ayer plan also envisioned using the British royal family to help foster the romantic allure of diamonds. An Ayer memo said, "Since Great Britain has such an important interest in the diamond industry, the royal couple could be of tremendous assistance to this British industry by wearing diamonds rather than other jewels." Queen Elizabeth later went on a well-publicized trip to several South African diamond mines, and she accepted a diamond from Oppenheimer.

In addition to putting these plans into action, N. W. Ayer placed a series of lush four-color advertisements in magazines that were presumed to mold elite opinion, featuring reproductions of famous paintings by such artists as Picasso, Derain, Dali, and Dufy. The advertisements were intended to convey the idea that diamonds, like paintings, were unique works of art.

By 1941, The advertising agency reported to its client that it had already achieved impressive results in its campaign. The sale of diamonds had increased by 55 percent in the United States since 1938, reversing the previous downward trend in retail sales. N. W. Ayer noted also that its campaign had required "the conception of a new form of advertising which has been widely imitated ever since. There was no direct sale to be made. There was no brand name to be impressed on the public mind. There was simply an idea -- the eternal emotional value surrounding the diamond." It further claimed that "a new type of art was devised ... and a new color, diamond blue, was created and used in these campaigns.... "

In its 1947 strategy plan, the advertising agency strongly emphasized a psychological approach. "We are dealing with a problem in mass psychology. We seek to ... strengthen the tradition of the diamond engagement ring -- to make it a psychological necessity capable of competing successfully at the retail level with utility goods and services...." It defined as its target audience "some 70 million people 15 years and over whose opinion we hope to influence in support of our objectives." N. W. Ayer outlined a subtle program that included arranging for lecturers to visit high schools across the country. "All of these lectures revolve around the diamond engagement ring, and are reaching thousands of girls in their assemblies, classes and informal meetings in our leading educational institutions," the agency explained in a memorandum to De Beers. The agency had organized, in 1946, a weekly service called "Hollywood Personalities," which provided 125 leading newspapers with descriptions of the diamonds worn by movie stars. And it continued its efforts to encourage news coverage of celebrities displaying diamond rings as symbols of romantic involvement. In 1947, the agency commissioned a series of portraits of "engaged socialites." The idea was to create prestigious "role models" for the poorer middle-class wage-earners. The advertising agency explained, in its 1948 strategy paper, "We spread the word of diamonds worn by stars of screen and stage, by wives and daughters of political leaders, by any woman who can make the grocer's wife and the mechanic's sweetheart say 'I wish I had what she has.'"