Buy an engagement ring

Advice from Peter Schneirla, the chief gemologist for Tiffany & Co, before Valentine's Day.

Peter Schneirla, the chief gemologist for Tiffany & Co, knows a lot about diamonds. So much so that he has his own set of principles - cleverly titled the Peter Principles - for love-struck men shopping for engagement rings. Schneirla, who advises customers on selecting diamonds, was in town recently for the opening of the new store in the Dubai Mall and passed on some advice before Valentine's Day.

The first Peter Principle is know your merchant. Face it, unless you have the word "gemologist" in your job title, you probably don't know much about diamonds, and you're not going to become an expert quickly. "Buying a diamond is a blind purchase to the uneducated," says Schneirla, who has been in the business for more than 20 years. "My job is to find out what you know. That's the most important thing. You have to work with someone who is going to ensure you are getting the most with your purchase."

Visit a few sellers to see who wants to help and who wants to hawk zirconia. "People need to get educated," Schneirla says. "And that's really to protect themselves. Any reputable merchant is going to put in the time to do that." Unsurprisingly, getting educated is the second principle. Begin by determining how much you want to spend. "The last time I checked, it was two months' salary," says Schneirla, adding that it is really up to the man. "Diamonds are varied enough in their quality that anyone can find something that's meaningful."

Not to mention they are a good investment, as diamonds hold their value in a recession. The standard method to quantify a diamond's quality are the Four Cs: cut, colour, clarity and carat. The latter is the only definitive measurement of a diamond's worth, while the others are "a melding of art and science". "Put your money where your colour is," Schneirla says about the most important C and his third principle. "A good-colour diamond is one that is really free from colour."

The colour scale runs from D (which is colourless) to Z. "The difference between a D and H to me is black and white," he says. "To a lay person, they're identical." The merchant should be able to tell you the diamond's colour grade. But what really matters is what can be seen with the naked eye. So don't bother looking through a diamond loupe, the round magnifying glass that the merchant might be holding. You won't see anything ("it's a skill you have to practise"), although the seller should allow you to use a binocular microscope, which can spot smaller imperfections.

After colour, look at the cut. A diamond's optical potential can only be brought out through proper cutting. "We've seen that there are a lot of new cuts of diamonds out there," Schneirla says. "For most of my career, there weren't a lot of variations in cuts." And if you are going to go with something different, consult the person who will have to wear the ring. "Quite frankly, most women make their mind up on this very quickly, and they're usually right," he says.

If you don't want to spoil the surprise, stick with a traditional round stone, then an emerald cut. And if you insist on being unconventional, he suggests Tiffany's Lucida and pear cuts, which he describes as "brilliant". To judge a good cut, watch how the light refracts out of it. Diamonds are usually either too deep or too shallow, which cause light leakage. "Look for even brilliance across the top: lots of sparkling, overall brilliance from inside and outside."

If it is dark inside or outside, "you've got trouble". Fortunately, Schneirla says, "that's really easy to see after a few minutes." Finally, he says consumers can also prepare themselves by reading about diamonds. Tiffany & Co offers a booklet online at www.tiffany.com. Research and patience are important, because diamonds do actually last for ever. And Schneirla followed his own advice when he bought an engagement ring. While he had all the extra knowledge eluding most men, he stuck with a simple yet gorgeous oval cut with an E colour.

He also didn't burden himself with concern about the mounting - the final principle. "A lot of people make the mistake about being over concerned with the mounting. It's minimal in terms of the value of an engagement ring." John Mather