Rules of engagement

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Kate Middleton sporting her sapphire and diamond engagement ring. (DAVID CHESKIN / THE ASSOCIATED PRESS)

Diamonds may still be a girl’s best friend, but the colourless rocks are no longer the clear and obvious choice when it comes to engagement-ring bling.

Today’s brides-to-be are bucking tradition and announcing their status updates to the world with sparkly stones in a rainbow of colours.

A sapphire is forever, too, apparently. So is the ruby.

Or how about popping the question with a green garnet to match your beloved’s eyes?

The reason the diamond is being forced to share the spotlight with other precious gems probably has something to do with the 18-carat blue sapphire that Prince William slipped on Kate Middleton’s finger to seal their betrothal. (Never mind that it was his mother Diana’s engagement ring, too.)

Rubies, meanwhile, got a PR boost when former NFL player Eric Johnson proposed to Jessica Simpson last November with a five-carat version of the singer’s birthstone.

Whatever the motivation — celebrity influence, family heritage or individuality — there are things to consider when choosing a centre stone for a ring that’s meant to be worn day in and day out, ideally for many years.

"Diamonds wear like steel, whereas most coloured stones will eventually show signs of wear. Stay away from the soft gemstones," says Tom Sutton, owner of Sutton’s Custom Smithworks and a 34-year Winnipeg goldsmith.

Emeralds, for example, are rarer than diamonds by far — carat for carat they’re usually more expensive too — but "they’re notoriously soft and they crack, chip and flake."

Tanzanite, found only in the foothills of Mount Kilimanjaro, is the "latest sweetheart" of gems, says Sutton. It comes out of the ground orangey brown and heats up to an "exotic, vivid blue, kissed by purple hues," according to the American Gem Trade Association, which made tanzanite the first birthstone (December) added to its list since 1912.

Unfortunately, it’s another softie. Opals are even worse.

Sapphires are the most popular coloured gem to use in engagement rings, Sutton says, and for good reason. They rate a nine for hardness on the Mohs scale, second only to diamonds, which are a 10. (Anything lower than an eight is not recommended for an engagement ring. Emeralds registers between seven-and-a-half and eight.)

Although its name is derived from the Greek word "sappheiros," meaning "blue stone," sapphire is actually the mineral corundum, which comes in virtually every colour of the rainbow.

Ruby is just a fancy name for red corundum.

If you do decide to go with a sapphire or a ruby, pay attention to the intensity of the stone’s colour, Sutton says. The best sapphires are cornflower blue while the dark blue, almost black ones are commercial grade.

"When you see a sapphire, you want to see colour and brilliance, not just a dark spot that looks like coal."

A pinker ruby will be less expensive than a pure red one.

While the majority of their clients still want a white diamond, Marie Christoffersson, co-owner of David Rice Jewelry + Objects, says the 40-year custom design business has always promoted coloured gemstones as a diamond alternative.

"They’re just more rare and unusual. We just did a star sapphire set in white and yellow gold. It was a very beautiful pale blue with a perfect star," she says.

"Sometimes, instead of a diamond, customers will choose a very delicately coloured gemstone, like a pale pink sapphire or a pink tourmaline."

Other clients still want diamonds, but to complement or accent a coloured centerpiece.

Besides durability of the stone, another important thing to keep in mind, Christoffersson says, is wearability. "Red or green might be your favourite colour, but do you want to wear that colour every day for the rest of your life?"

And while Kate Middleton probably won’t have to subject her 18-carat corundum (which is surrounded by 14 diamonds) to dishwater and other hazards of domesticity, a commoner’s bling has to withstand a lot of wear and tear.

While sapphire and diamond are only a single point apart on the Mohs hardness scale, the latter is still four times as tough.

"It’s not a close second," says Lisa Malbranck, gemologist and jewelry designer at the Diamond Gallery.

"Over time, you will see the wear on any coloured gemstone. You can nick and chip a diamond, but they’re much more durable."

Combining the two is a popular option, says Malbranck, (George W. Bush’s daughter, Jenna Bush Hager, has a diamond engagement ring flanked by two sapphires) while coloured diamonds offer the best of both worlds — for all budgets.

Yellow diamonds are really popular right now, she says. (Carrie Underwood, Heidi Klum and Rebecca Romijn are all sporting one.)

"We have a two-carat yellow cushion-cut diamond set in platinum for $33,000, but you can also get a beautiful yellow diamond in the $1,000 range."

(For more information on selecting a gemstone, check out the Gemological Institute of America (www.gia.edu) or the American Gem Trade Association (www.agta.org/gemstones).

carolin.vesely@freepress.mb.ca