A rich assortment of top diamonds and gems, heritage jewellery and signed pieces are the stars of upcoming fine jewellery auctions.

Christie’s Magnificent Jewels auction, scheduled for November 11, will present more than 100 jewellery pieces, including three important private collections spanning over a century of craftsmanship and gemmological excellence. 

Headlining the auction is the Mellon Blue, a fancy vivid blue diamond of 9.51 carats, once belonging to American horticulturalist, philanthropist and art collector Bunny Mellon. The piece has a pre-sale estimate of US$20 million to US$30 million.

Another highlight is a trio of notable private collections. A Splendid Casket of Ancestral Jewellery featuring ruby pieces is part of a distinguished collection inherited by Helena Violet Alice (née Fraser), Third Countess of Stradbroke (1874-1949). The pieces represent some of the finest surviving examples of Victorian craftsmanship, showcasing gemstones of a size and quality rarely seen outside of royal collections of the period. At the Coronation of Edward VII in 1902, Countess Helena wore a ruby and diamond star brooch valued at US$1.4 million to US$2 million, complemented by a ruby and diamond tiara, which has a pre-sale value of US$360,000 to US$600,000.

Meanwhile, the Rainbow Collection is one of the most extensive and conceptually coherent private collections of fancy colour diamonds, comprising over 300 natural stones of varying cuts and carats, spanning the full chromatic spectrum: Red, blue, green, yellow, orange, pink and grey. Each diamond was selected for its ability to represent a singular, unrepeatable hue. The collection is expected to sell for US$2 million to US$3 million.

A Private JAR Collection completes the trio. This is the second-largest JAR collection ever to appear at auction, consisting of 25 exceptional pieces, led by a fancy purplish-pink natural colour diamond ring of 8.68 carats valued at US$2.5 million to US$3.5 million. This follows the Marie-Thérèse Diamond, which set a new auction record for a JAR jewel when it sold for just under US$14 million at Christie’s New York in June this year.

Other highlights include a Burmese "Royal Blue" sapphire-brooch, featuring an impressive 65.46-carat cushion-shaped unheated sapphire, surrounded by nine colourless diamonds. This piece could sell for US$2.6 million to US$3.8 million, the auction house said. 

Premium coloured gems, meanwhile, will enjoy top-billing at Bonhams’ Hong Kong Jewels and Jadeite sale scheduled for November 23. The sale will also feature a selection of signed jewels and period treasures with creations by Bulgari, Cartier, Cerrone, Chaumet Paris, Dorera, Fred Paris, GF & F The Haute Joaillerie, JAR, M Gérard, Marcus & Co, Meister, Ronald Abram and Van Cleef & Arpels. 

Leading the sale is a pair of pear-shaped Colombian emerald pendants, weighing 64.37 and 63.19 carats, respectively. It has a pre-auction estimate of HK$1.8 million to US$3.5 million (around US$230,000 to US$450,000).

Another notable lot is a rare, unmounted oval Paraíba-type tourmaline weighing 160.75 carats of African origin. Bearing natural crystal-clear clarity and a coveted blue-green colour, it will be offered with an estimate of HK$2.8 million to US$5 million (approximately US$360,000 to US$640,000).