Bonhams leads June jewels sale with century-old Boucheron tiara, Cartier sautoir

Bonhams will open its June jewels sale with a lesson in how jewelry earns its price: not just through diamonds and design, but through authorship, provenance and survival. The 1924 Boucheron diamond bandeau tiara, unseen publicly for just over a century, carries an estimate of £200,000 to £300,000, and it arrives with the kind of documentation that collectors prize, including a May 2026 Boucheron authenticity report.

The tiara was commissioned in London on 18 July 1924, four months before Doris Mary Thérèse, Baroness Ashburton, married Alexander, 6th Baron Ashburton. Its trail runs through Mary Ethel, Viscountess Harcourt, and the piece still reads as a compact, disciplined example of early 20th-century high jewelry: an inner circumference of 48.0 cm, a height ranging from 1.0 cm to 4.2 cm, a principal old brilliant-cut diamond of 3.60 carats and about 85.00 carats of remaining old brilliant and old single-cut diamonds. The design is classical in feeling, with stylised olive leaves that lend the tiara the calm geometry of Art Deco while carrying the symbolic language of peace, hope and prosperity.

That is the first practical lesson for anyone evaluating heirloom-style diamond or birthstone jewelry. Signature matters. So does a clear chain of ownership. So does the survival of the original structure, whether that means a bandeau tiara retaining its proportions or a pendant keeping its original clasp and numbering. In modern birthstone pieces, the same signals can make a ruby ring or sapphire pendant feel collectible rather than merely decorative: a named maker, a documented commission, a period-true motif and careful workmanship at the setting line, whether bezel or prong, that matches the era and the stone.

Bonhams’ other headline jewel makes the point from a different angle. A Belle Époque Cartier seed pearl and diamond sautoir, circa 1910, from the collection of Dame Nellie Melba, is being offered at auction for the first time since Melba owned it. Signed Cartier Paris and numbered 2099 on the clasp and pendant, it features seed pearl linking, millegrain-set old brilliant, old single and rose-cut diamonds, and a circular pierced pendant with a radiating floral motif. Bonhams has estimated it at £60,000 to £80,000, a range that reflects both its maker and its unusually vivid provenance.

The sale brings together six notable single-owner collections and jewels spanning the Napoleonic period to the 21st century, but the strongest signal is narrower and more enduring. Pieces with documented origins, crisp period design and original signatures hold their own better than generic jewels, and that is as true for a century-old tiara as it is for a modern birthstone ring.