In Sex & the City terms, black diamond is a Carrie, white diamond is a Charlotte. In fact, Carrie Bradshaw's black diamond engagement ring from Sex and the City 2 is five carats. Its dramatic statement started a worldwide trend for alternative engagement rings that's still going strong today.
Trendsetter though she may be, Carrie isn't the first: Carmen Electra also has a two-carat black diamond engagement ring. Carole Lombard received a black diamond ring from Clark Gable too.
What are black diamonds? Black diamonds are real diamonds, crystallized carbon. The color is caused either by dense graphite inclusions or by a safe form of irradiation that turns lighter color diamonds a green that’s so dark it appears black. Which should you choose? Enhanced black diamonds have fewer fissures and spots than natural blacks, which often have so many inclusions that they are less durable.
Natural color black diamonds will be more expensive than treated black diamonds, which are more affordable than colorless diamonds. If you decide you want a natural fancy black diamond, make sure your black diamond is accompanied by a GIA grading report that confirms that the color is natural and not treated.
To judge the quality of black diamond engagement rings, you can't use the same 4Cs as colorless diamonds. More color is better: your black diamond should be an even black. Internal clarity and cut proportions really don't matter since you can't see in the dark. If you look closely at the surface you are likely to see surface blemishes like small fissures and spots: make sure that none of them are near the girdle because they could be vulnerable to chipping.
Black diamonds generally weigh a bit more than white diamonds with the same dimensions since they are often cut deeper to maximize the color, so make sure you look at the millimeter size as well as the carat weight when you're comparing them. Larger sizes are more expensive per carat and more difficult to find without some surface features like spots.
If you want the look of black diamond in a more affordable gem, black sapphire and black spinel look very similar to black diamond and will have fewer surface spots.
Black diamonds may not sparkle but they definitely shine. That's known as "adamantine" luster and it's something that diamond does better than other gems, black or white.