The practice of a smitten man on bended knee offering the object of his affection a diamond ring in exchange for a promise of marriage is now standard practice. Credit clever advertising by diamond industry giant De Beers for making both the practice and the associated costs part of global courtships. Investigative journalist Edward Jay Epstein laid out the history of De Beer's campaign for gemstone ubiquity in his book The Rise and Fall of Diamonds: The Shattering of a Brilliant Illusion (Simon & Schuster, 1982). In the 1930s, after two decades of plummeting diamond sales due to World War I and the Great Depression, De Beers hired the firm N.W. Ayer to develop a national advertising, PR and marketing campaign intended to get its profits back on track. Engagement rings were already fairly common. What De Beers hoped to accomplish was to make the practice universal and more profitable. Because the majority of stones sold were of lesser quality and cost, the goal was to equate true love with a high price point. Step one -- easily accomplished -- was to get movie stars and fashion designers to promote diamonds as an elegant and desirable accessory. From 1938 to 1941, diamond sales spiked by more than 50%. The next step was the dropping of tidbits in newspaper society pages about elegant and enviable diamond engagement rings. DeBeers also unleashed a slogan that endures today: "A Diamond is Forever." Year by year, unyielding campaigns helped fuel ever-increasing sales of diamond engagement rings. By 1965, De Beer estimated that roughly 80% of American women got a diamond ring as part of their proposal. "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,'" Epstein writes. "It further claimed that 'a new type of art was devised ... and a new color, diamond blue, was created and used in these campaigns.'" Not content with sparking a sparkling tradition, De Beers and its agency set to work influencing what hopeful grooms-to-be should shell out. Initially, in the 1930s, they pushed the notion that a ring should cost the equivalent of one month's salary. More recently that's been redefined as two months of salary. Using the template that brought it great success, De Beers applied a similar strategy to increase sales outside the U.S. as well as to introduce the concept that husbands owe their wife yet another diamond to celebrate their 25th anniversary.