Forked

In 1970, the average size of a new home was about 1,500 square feet. Today, it’s about 2,521 square feet, which is 68 percent larger. There are fewer people living in the average home, too, so each person has more space. In 1970, each resident of a home occupied 478 square feet, on average. Today, each person occupies 996 square feet. Many kids get their own bedrooms, some kitchens rival those in restaurants, and 90 percent of new homes have a garage.

This handy mnemonic — color, cut, clarity and carat — was developed in the 1940s by the Gemological Institute of America, still the world’s premier diamond-grading company. Lore holds that every diamond is unique and a work of nature’s art. But this idea was intimidating to American customers who wanted a firm readout of a diamond’s worth before buying it. De Beers therefore loved the Four Cs, and the company sent speakers on a promotional tour to explain these standards as if they had been observed for centuries. But when it comes to the most popular kind of diamond — the round, brilliant-cut stone that is a staple of engagement solitaires — a key factor embedded in the cut rating is likely to have a big impact on value. The “depth percentage,” the relationship between the stone’s top and the angle of its slanted sides, can make a diamond’s glitter a little more spectacular thanks to the physics of light. The sweet spot? A ratio of 58 to 60 percent. Too many buyers of stones of less than two carats get hung up on minor gradients of color and clarity, which are invisible to the naked eye and meaningful only at the cash register. For those who don’t plan to routinely ogle their stone under a microscope, an easier formulation would be the Two S’s: size and sparkle. The resale value of a diamond drops between 30 and 50 percent the moment you walk out of the store with it (a sixth myth is that they are good investments; they aren’t) so you might as well enjoy its illusory light while you can.