Howard—whose upcoming book, The Business of Brides, details the rise of the wedding industry between the 1930s and 1950s—explains that the modern engagement ring's story really begins with the discovery of vast quantities of diamonds in South Africa in the late 1860s. Diamond jewelry of all kinds became more and more popular in subsequent decades, but the industry fell on hard times in the 1930s, due to the Depression and its accompanying plummeting marriage rate. Soon the DeBeers diamond cartel had a surplus. "So they tried to promote the diamond engagement ring," she says. DeBeers put New York’s N.W. Ayer advertising agency on the case, and in 1948 they hit pay dirt with the slogan "A Diamond Is Forever." This hypnotic mantra has seduced America ever since, calling out from magazine and television ads, billboards, and bus shelters.

The Ayer agency came up with other ways to get couples' attention. "They created short ?lms about diamond engagement rings that they would show before feature ?lms, at women's clubs, churches, high schools, colleges," Howard says. "It was kind of like you couldn't escape it at that point. I have a 1955 statistic from the ad agency that said that between 75 and 85 percent of brides had diamond engagement rings."

We're still hooked. The diamond jones has become part of our cultural DNA. The number we buy, the amount of money we spend (or cause to be spent), and the size of the stones we favor all have increased steadily. It appears this is one accessory that will never go out of style. Jewelry and fashion expert Michael O'Connor will tell you, however, that brides-to-be de?nitely are affected by trends that mirror the emotional state of our culture.

"Right now, people are really looking back to antique and vintage pieces, looking to them for comfort," O'Connor says. "These are pieces we all remember from when we were younger: 'This looks like my mom's ring, my grandmother's pin.' Celebrities and stylists want authentic vintage pieces for award shows, and a lot of designers are re?ecting that trend."

The other big in?uence, he says, is a counter-trend toward classic, straightforward lines. "Everyone's so overloaded because of everything we have going on in the world. We're looking forward with the view that 'I want everything in my life to be as simple as possible'." (Though not, of course, so simple that we'd skip the sparkler altogether.)

As always, Hollywood helps set the trends. Unprompted, O'Connor rattles off a bevy of celebrity-ring details: "Jessica Simpson-pear-shaped with two brilliants, very classic. Anna Nicole Smith-marquise with tapered baguettes. Melania Knauss, Donald Trump's intended [now wife]-emerald shape with tapered baguettes. Jennifer Aniston had a much more romantic, frilly kind of style. Sarah Michelle Gellar, she has a princess cut." And he notes that J. Lo's big pink ring from (then fiancé) Ben Af?eck ushered in a colored-diamond trend that has outlived their relationship.