Bonhams leads London sale with Boucheron Harcourt diamond tiara

The 1924 Boucheron Harcourt diamond bandeau tiara is the kind of jewel that tells collectors exactly why signed 1920s maison work still matters. Bonhams is placing the openwork bandeau at the head of its Exceptional Jewels sale in London on 11 June 2026, and the piece arrives with the markers serious buyers watch for: a Boucheron authenticity report dated May 2026, a fitted Boucheron case from 180 New Bond Street, and a documented line of ownership from Mary Ethel, Viscountess Harcourt, to her daughter Doris Mary Thérèse, Baroness Ashburton, then by descent.

The tiara’s construction is as important as its sparkle. Bonhams says the design was commissioned in London on 18 July 1924, four months before Doris Harcourt’s wedding to Alexander, 6th Baron Ashburton, on 17 November 1924. At its center sits a pear-shaped drop and a principal old brilliant-cut diamond weighing 3.60 carats, set among scrolls, quatrefoils and stylised olive leaves. The remaining old brilliant- and old single-cut diamonds total approximately 85.00 carats, giving the bandeau both scale and restraint, the sort of balance that defines high-level interwar design.

For collectors, the tiara is not just an auction trophy; it is a clean case study in how authenticity is built. The commission date, original case, Boucheron documentation and uninterrupted provenance all work together, while the classical antiquity influence and olive-leaf motifs add the design history that separates a wearable jewel from a museum-grade object. Bonhams has estimated the piece at £200,000-300,000, a figure that reflects both the house name and the survival of the jewel in notably intact form.

The sale is broader than one tiara. Bonhams says Exceptional Jewels brings together period and antique jewellery from six notable single-owner collections, including a circa 1910 Cartier seed-pearl and diamond sautoir from the collection of Dame Nellie Melba, offered for the first time since her ownership and estimated at £60,000-80,000. Jean Ghika said the Cartier jewel reflects the elegance of the Belle Époque era and Cartier’s early pioneering use of platinum. Bonhams is also lining up a rare Art Deco ruby and diamond swag necklace by Sterlé that converts to a bracelet and clip, alongside a 5-carat Colombian no oil emerald ring by Bulgari, a 20-carat Fancy Deep Brownish Greenish Yellow diamond ring, a 25-carat unheated Sri Lankan sapphire ring and a 5-carat Kashmir sapphire ring. For vintage buyers, the message is clear: signed maisons, original fittings, strong provenance and thoughtful convertibility still define the best jewels.