Colin Shah inspects a diamond at Shah & Shah, which had been his family’s business going back to his great-grandfather. His clientele comes entirely from word of mouth. (Katherine Frey/The Washington Post)

I am gazing at nearly $500,000 in jewels spread before me on a table in a nondescript room several floors above Farragut Square in Washington.

As I nervously twist a $75,000 “untreated” two-carat diamond-cut Burmese ruby ring between my thumb and forefinger, I can’t stop looking over at the back slab of a safe a few feet away. It reminds me of the monolith from “2001: A Space Odyssey.”

I direct questions toward the 41-year-old proprietor sitting across from me in this most unlikely of jewelry stores.

The gentleman’s name is Colin Shah, scion of a Washington jewelry business stretching back to the eve of the 1929 stock-market crash.

Shah has put his family’s jewelry trade in a time machine and turned it back to the speakeasy approach that great-grandfather Izzy used when he ran it in the 1930s.

There is no storefront. No marketing. No signs. Shah & Shah boutique lies behind a door on the sixth floor of a downtown office building. You push a doorbell to get buzzed inside.

“You have to know we are here,” said Shah, a former personal trainer to several of Washington’s boldface names. “The nice thing is, both of my businesses have always been word-of-mouth.”

Shah has traded in his sweats for collared shirts and tailored jackets. The personalized attention he gave to the customers’ muscles is now focused on what they wear on their fingers, arms and necks.

Most customers are referred, which means they come in more positive than fearful, Shah said: “We don’t have to do that first dance of ‘I’m a nice guy you can trust.’ ”

A lot of hustle is involved. Word of mouth means socializing with clients, talking to people, attending parties. Last week, he held an open house with champagne and chocolates for Mother’s Day.

“We basically try to slow down the process,” Shah said of his sales approach. “I will spend an afternoon on a $2,000 sale. . . . It seems silly to me to expect someone to make so personal and emotional a purchase across the counter from a stranger.”

Everything is a throwback to the days of personalized jewelry sales. The walls include black-and-white photos of the family’s shops from the past. There is a photo of a young Jack Benny.

Shah wants every touch to hint at elegance. He plops down a beautiful silver candy dish filled with Edward Marc dark-chocolate nonpareils. He follows with a bottle of Hildon water, which looks like glass artwork that might be for sale.

Most of his business is in creating jewelry for the 2,500 customers on his client list.

“The major difference between Shah & Shah is we call you and say: ‘Hey, Tom. Christmas is around the corner. Susie was in last week, and after getting her rings checked and cleaned, she loves this gold chain. Can I send you a couple of pictures in case you find yourself needing ideas?’ ”

On the phone last week, he told me about two professional women who swung by after a lunch that day to discuss updating their wedding rings and ended up spending between $5,000 and $6,000.

“By the end,” he said, “one had bought a ring and dropped off jewelry for me to redesign. The other dropped her wedding set off.”

Shah did more than $2.3 million in sales last year. He will redesign a ring for $900, sell you engagement rings for $1,700 or $3,500, sell you hard-to-find, inexpensive quartz and Swiss automatic-movement watches. Or you can spend $150,000 on a diamond ring, like the one Shah delivered to a Midwest bigwig after showing the gem to a couple at New York’s Four Seasons hotel.

Profitability can run well into the middle six figures.

“I have not lost money since I have been here,” Shah said.

His great-grandfather Isadore Shah immigrated from Poland in the early 1900s with a few gemstones and a reputation in the trade. He opened a store a couple of doors down from a relative’s eyeglass shop on F Street NW.

Izzy’s family kept the business going until the late 1960s, when Shah & Shah closed for more than a decade. Colin’s father relaunched it at 17th and K streets NW, where it is currently located.

“It was such a grind,” Shah recalled. “My dad did appraisals every night on the dining-room table.”

His father built the business into a jeweler that created pieces to fit each client.

“Dad was all about survival,” Shah said. “People couldn’t afford pre-made big-box jewelry. He came up with designs that fit their budget.”

Colin refers to his niche as “bespoke,” commissioned to preferences.

He grew up in a middle-class environment. The self-described “spirited” teenager joined the Army upon high school graduation in 1993 and became a gunner on a Bradley Fighting Vehicle in Germany.

He came out of the Army 1996 a mature adult, having learned accountability, self-reliance and responsibility. He joined his father in the family trade.

In his spare time, he worked as a personal trainer in Washington. But the father-son team wasn’t perfect, so he became a full-time trainer. Through word of mouth, starting with a curator for a museum, he developed a clientele of upscale, mostly older Washingtonians who paid him up to $150 to come to their homes for 50 minutes and keep them mobile and fit.

“My niche was post-rehab fitness or diet,” he said, and Colin Shah Personal Training Inc. was his life for 13 years, from ages 22 to 35. “It was a high level of personal service.”

His clients included Washington Post publisher Katharine Graham, the wife of violinist and conductor Pinchas Zukerman, Atlantic Media owner David Bradley, and former secretary of state Madeleine K. Albright.

“I had a really good clientele,” Shah said. “I was probably pushing $200,000 a year at my height, but it was 12-hour days, 7 a.m. to 8 p.m. I even traveled with them.”

He flew to Europe occasionally to “tune up” an ambassador who tried to stay in shape. He flew to Ottawa for the Zukermans. His client list took him to funerals, weddings and graduations.

His father called in 2010 and asked if he wanted to take another run at the family business. Shah bought his dad out two years later.

At the time, the business was grossing nearly $3 million in sales per year, and had been run the same way for 30 years. Shah attacked fixed costs that his father allowed to fester. He saved $25,000 a year replacing old computers, phones, his website and outside consultants.

“I moved everything in-house,” Shah said. “There were a lot of latencies.”

He cut out the middleman from his diamond purchases, saving tens of thousands of dollars per year. The lowered costs allowed him to charge less but still boost the bottom line.

Shah is still upgrading the database system, which has contact information, preferences, sales and intangibles such as birthdays and anniversaries for 2,500 select clients.

He circulates through evening events up to four nights a week, schmoozing clients and building relationships with new ones.

“People introduce us to other couples as their personal jeweler,” Shah said. “Everyone should have their own jeweler.”