Jessica McCormack has always preferred a home to a homepage. Her five-storey Georgian townhouse on Carlos Place in Mayfair is the embodiment of her eponymous jewellery brand, reflecting her vast array of inspiration and impeccable taste with a rotating contemporary art collection, exuberant textiles, curious ephemera and a library of books.

Paintings by Frank Bowling and Basil Beattie currently adorn the walls, while a cloud of pampas grass hangs from the ceiling and anemones are arranged in antique marmalade jars. Upstairs, a self-playing piano tinkles by a large bay window. “Everyone says that retail is dead but it definitely is not,” she asserts. “You just need to work a little harder to entice customers.”

Designed entirely by McCormack, the boutique demonstrates her unique knack for effortlessly fusing antique and contemporary aesthetics. She is London’s reigning queen of modern, wearable diamonds, presented in pieces created using time-honoured techniques and packed full of personality and symbolism.

McCormack grew up in Christchurch, New Zealand. Her father was an antiques dealer and she spent her childhood surrounded by unusual furniture and objets d’art. “He would take me to auctions and I would always buy the box of grandmother’s jewellery in a lot. I would take each piece apart and build it back together, but it was never anything precious.”

McCormack moved to London aged 25 to take up an internship at Sotheby’s, after, in her own words, a year of pestering letters to the auction house’s head of jewellery. Sotheby’s ignited her appreciation and understanding of precious jewellery design. “Until then, I had never seen Russian crown jewels and vintage Cartier and Suzanne Belperron pieces. What I really noticed is that when you picked something up, it really felt like a piece of jewellery.”

It was also at Sotheby’s that she met Michael Rosenfeld, a third-generation diamantaire who would become her business partner. With Rosenfeld’s backing, she opened her appointment-only workshop in Clerkenwell in 2008. Rihanna was one of her first customers. “A girlfriend of mine in New York was wearing the Wings of Desire earring and Rihanna’s stylist loved it. Rihanna came to London and bought it – it’s hallmarked as the first commercial piece that I ever made.”

Rachel Slack, a member of the South African Oppenheimer dynasty, joined as a partner in 2010, after McCormack remodelled a millennium diamond gifted by her father, Harry Oppenheimer. By then, McCormack’s client list included Madonna, Carine Roitfeld and a growing pocket of London’s high society.

The sweeping wing remains a bestselling motif of the house, alongside stars and swallows, the latter inspired by sailors’ tattoos. McCormack’s design signature is a Georgian-style cut-down setting and blackened gold, which adds a subtle punk edge to feminine pieces. Jewellery is hand-drawn by McCormack and brought to life in the on-site workshop, using stones sourced by Rosenfeld. “There is a holistic approach to the whole thing. People often go to Hatton Garden and then come careering back.”

Her ingenious Party Jacket ring is designed to wrap around another ring, be it an existing diamond solitaire or an outdated heirloom in need of a contemporary twist, thus allowing you to transform your jewellery into something entirely new. The idea was inspired by 18th-century keeper rings, worn as a protective cover for a more valuable diamond. “My father taught me to look at things from a different perspective and place them in a new context, and that is what I do with diamonds. Even though some pieces are cooler, they are still pretty and feminine and romantic.”

The newest addition is the Gypset Bloom collection of dainty diamond dandelions, seedpods and lily of the valley flowers, suspended from 18-karat yellow gold hoops, which can be worn as singles or pairs. It is a fresh play on the hugely popular Gypset earrings, worn by Meghan, Duchess of Sussex, Victoria Beckham and Emma Watson.

Much of McCormack’s business also comes through her self-run Instagram account, where she styles finger stacks of diamonds with jeans, white T-shirts and oversized tailoring. “We’ve had six-figure sales that have come through Instagram. People can relate to it because it’s real life, not red carpet.”

The convention-flouting McCormack has helped redefine how women wear fine jewellery, creating pieces that fit the contemporary customer’s modern wardrobe and lifestyle. “I take the craftsmanship and the design of my jewellery very seriously, but I also have fun with it. You should be able to go for breakfast; to a board meeting; out for dinner and dancing on tables, and still be wearing the same jewellery.”

For those wondering where to keep their precious pieces, McCormack offers beautifully crafted jewellery boxes, made from repurposed apothecary cabinets and 19th-century coffers, lined with faux suede. Each one is stitched with motifs and messages by Hand & Lock, the Queen’s embroidery house of choice, which was recently issued with a Royal Warrant. The boxes start from £20,000 and there is currently a six-month waiting list. She made the first box for her daughter, Estelle, creating compartments with personal messages intended for different times in her life.

“I always encourage my clients to write notes about each piece that they buy, because you don’t want to lose your stories. It’s not a monetary thing, it’s about capturing the romance and emotion of the moment.”