Ah, the holidays.

It’s the perfect time to buy something significant for a special person—you know, show them you care. And it’s the perfect time to freak out about how, exactly, to do it.

Jewelry is an intensely personal way to express style, even for men. (Don’t try to tempt your tweed-wearing friend with an Apple Watch—he will recoil.)  If you’ve got someone in your life with even the barest shred of personal style, approach the endeavor with eyes wide open and ears curled toward every hint of preferences that float your way.

It is possible to win this challenge. It just takes some effort. 

A Cartier Burmese ruby ring in the Egyptian Revival style. Source: Falcone Studios

The main thing is to know what you don’t know. So I met Fiona Druckenmiller at her Upper East Side shop to  seek her best advice for buying gemstones. She’s got credibility: As one-half of the multibillion-dollar Druckenmiller fortune, she presides over FD Gallery, a six-story townhouse full treasures from the likes of Société Cartier, Van Cleef & Arpels Inc., JAR, Verdura, Hemmerle, and Viren Bhagat. Walk through the heavy, double-door portal and you’ll find yourself amid glittering items worth hundreds of thousands of dollars apiece. Her clients range from Upper East Side doyennes and French financiers to young, Asian entrepreneurs and Italian barons.

Druckenmiller wants to make it clear: “Just because you’ve bought an engagement ring doesn’t mean you know how to buy gemstones.” It’s solid advice, and a great place to start. Here’s what else you need to know if you are in the market for some seriously fancy jewelry.

You can’t eyeball quality
Do you know the difference between heated and unheated rubies? Can you spot an emerald that has been oiled, vs. one that contains no oil? Probably not. But those enhancements greatly affect the value of stones.

Inside FD Gallery, on Manhattan’s Upper East Side. Photographer: Stephanie Hedges

“People have been heating stones for hundreds of years to enhance the color,” Druckenmiller says. “But a Burma ruby that is unheated is going to be worth 10 or 20 times as much as a heated ruby from Africa.”

As for emeralds, many have little fissures in them, because emerald can be brittle. Jewelers often use oil to make the cracks less visible. So an emerald with no oil will naturally be more valuable than one that has been altered.

“It’s not something you can look at and tell,” says Druckenmiller. “People just don’t know. It’s not that they’re wrong to buy them. It’s just inexperience.”

The best way to find out what kind of quality you’re dealing with is to inquire, simply and directly. Question the seller as to where the jewel originated  and how it has been treated. Ask to see the certification papers. And bring along an expert, or a well-trained friend, to act as backup and offer a second opinion.

While such brand-name emporiums as Harry Winston Inc., Tiffany and Co., and K. Mikimoto & Co. offer plenty of beautiful and expensive pieces, they also build additional costs into their prices as well. Glamorous stores require hyper-expensive real estate, with advertising campaigns and red carpet events costing millions each year. It’s all built into the cost structure of each big brand.

What’s more, these brands don’t necessarily offer the highest-quality stones. (Also keep in mind that lower-end big-box jewelry stores sell stones grown in laboratories, a practice so pervasive that this year the Diamond Producers Association launched a marketing campaign called “Real is rare” to emphasize the importance of genuine stones and to bolster business, especially among millennials.)

Small retailers and private boutiques can sometimes offer better value on high-quality jewels because they have lower overheads than big retail stores and diamond houses.  Photographer: Stephanie Hedges

For instance, Mikimoto sells plenty of cultured pearls. The value of a cultured pearl can be just 10 percent that of a natural pearl. If you want the most natural, rarest item at the best price, you may want to look elsewhere.

“Learn as much as you can and find a trusted source, who also could help you learn,” Druckenmiller says. To find the best authentic items at fair prices, visit small, boutique shops and trustworthy private dealers, as well as auctions and estate sales.

At auctions, be persistent
If you do take your chances at public auctions and sales, be prepared to go up against dealers, retailers, and brand-name houses such as Cartier and Van Cleef, which often buy back important estate- and museum-quality jewelry to keep in their archives and exhibit worldwide. Why wouldn’t they? The supply of significant jewels and gem stones dwindles every year, thanks to inevitable loss, irreparable damage, and collectors who squirrel items into private coffers.

The major gem auctions—think Sotheby’s, Phillips, Bonhams, Christie’s—typically start in November in Geneva and run through December. Industry insiders who attend them “will be very involved” in the first group of auctions, Druckenmiller says. Then they retreat.

“When it gets to be a week before Christmas, they have likely already spent their money or they have gone on to other things—so you can find bargains,” she says. “This will even happen just at the later end of night sales, when they are dropping out, or their attention wanders. But you have to be lucky. It’s a matter of being really vigilant.”

FD Gallery includes six floors of rare diamonds, modern and vintage jewelry, timepieces, and art by the likes of Keith Haring and Andy Warhol. Photographer: Stephanie Hedges

Refuse to accept old or inferior certificates of authenticity
When you talk to a dealer or retailer, always request certificates of authenticity for any gem.

One of the signature items by Van Cleef & Arpels is the ballerina brooch. Source: Falcone Studios

Look to ensure that the lab certification is from a trusted source (the Gemology Institute of America is the most reputable). GIA’s certification confirms the geographic origin, grade, and quality of stones after the institute has determined an item’s gemological identity, alterations, and origin. The place where a gem originated is important because certain countries, regions, and mines are renowned for the quality of their stones.

It’s also vital that certification papers are current. Two years old? Fine. Ten years old? Not acceptable.

“If you go to a dealer and they try to sell you a ruby or a sapphire, and they show you a certificate that is from 2008, I wouldn’t trust it,” Druckenmiller says. Lab technology has improved exponentially in recent years.

“I have seen labs that said in 2008 that a ruby is from Kashmir, but now we are finding out it’s from Madagascar,” she says. “That stone from Africa is worth a tenth of what it would be worth if it was from Kashmir.”

Don’t underestimate the law of supply and demand
As mentioned above, the supply of top-notch vintage Cartier and Van Cleef jewelry and valuables declines yearly. But buyers in Asia continue to feed the region’s voracious demand for known and historic brands, including those and Tiffany, Hermès International SA, and Chanel SA.  

The imbalance elevates prices.
“It’s the historic names they know, so every year in those niche markets, the demand goes up and the supply goes down,” Druckenmiller says. This is markedly different than buying something in a modern retail store, where lab-grown gems and cultivated pearls, plus costume-style jewelry and altered stones, can be supplied indefinitely.

Combat this by focusing your eagle eye on auction results. Those can give a good indication of current market rates.

Ruby and diamond ear clips by Cartier. Source: Falcone Studios

“One thing you could do is ask whoever you’re working with, whatever jeweler you go to, if they have a shop: ‘Can you show me auction comps for similar items?’” Druckenmiller says. “That’s a really good way to get a yardstick on valuations. So if you’re looking at a Cartier Art Deco diamond bracelet, and you see a similar auction result, it might not be exactly the same piece, but if the width is the same, it can give you a good idea for what something similar might be worth.”

If the dealer won’t share auction comps with you, walk away. 

Know your audience
The biggest stumbling block to buying jewelry for someone else often comes from simple oversight—buying a piece, such as a ring or bracelet, that doesn’t fit the personality of the receiver.

“Try to understand the lifestyle of the person you’re buying for,” Druckenmiller says. “Is she active? Does she use her hands for her job? That person might need something more lightweight, or made from more durable materials, than someone who [leads a more manicured] life.”

Titanium, platinum, and diamond are options more rugged than, say, garnet, opal, and gold.

If the person you’re buying for often wears big rings and chunky bracelets and necklaces, it’s a good bet she’d like more in a similar vein. If she tends to wear only delicate stud earrings or a thin band around her ring finger, it’s likely she’s a minimalist.

She might even prefer a wristwatch, Art Deco box, or vintage cigarette lighter to traditional jewels. Notice what jewels she wears—if she wears any at all—and select your purchase accordingly.

Do a little research into history
Do your homework. It pays to know the history of jewelry, especially as it relates to fashion and culture. Before YSL and LaCroix were sending Byzantine-inspired costume jewels down the runway, Coco Chanel did it. And she did it best: Chanel’s baubles, brooches, and chains inspired generations of fashion designers in the 1970s and ‘80s. Her work carries more cachet, especially if previously owned by someone notable—a royal or a celebrity.

It’s very simple, Druckenmiller says: “Age adds to value. And provenance matters.”