Lot 188. An impressive fancy-coloured diamond two-stone pendant. Estimate £1,200,000 - 1,500,000 (€1,300,000 - 1,600,000). Photo: Bonhams.

LONDON - A Fancy Intense Blue diamond, a Fancy Gray-Blue diamond and a Kashmir sapphire ring will lead Bonhams London Fine Jewellery sale this September.

The sale of 188 lots includes a selection of white and coloured diamonds, sapphires from Kashmir, Burma and Sri Lanka, signed jewellery from Cartier and Van Cleef & Arpels, and the largest private collection of jewellery ever to come to auction by Anglo-Italian designer Andrew Grima.

Headlining the sale is A Fancy Intense Blue diamond estimated at £1,200,000-1,500,000. The pear- shape diamond, weighing 4.03 carats, has been in a UK private collection for over 30 years.

According to the Gemmological Institute of America, only one in 10,000 diamonds has a fancy colour, which makes such stones rare and highly sought after. Often referred as "miracles of nature", coloured diamonds have, on average, increased in value by 100 per cent over the past decade with blue stones showing the strongest growth over the past 12 months (+5.5%), according to the Knight Frank Luxury Investment Index*. (*Data to end of Q1 2017 supplied by the Fancy Colour Research Foundation.)

Jean Ghika, Head of Jewellery for Bonhams UK & Europe, said: "We are delighted to bring this exceptional stone to the market. Blue diamonds are extremely rare and highly coveted. We are looking forward to showcasing this stone, along with other selected lots in London, New York, Hong Kong and Geneva, where we anticipate considerable interest."

Lot 188. An impressive 4.03 carats fancy-coloured diamond two-stone pendant. Estimate £1,200,000 - 1,500,000 (€1,300,000 - 1,600,000). Photo: Bonhams.

The pear-shaped Fancy Intense Blue diamond, weighing 4.03 carats, surmounted by a square mixed-cut Fancy Blue diamond, weighing 0.63 carat, in a claw setting,brooch length 3.0cm

Note: Accompanied by a report from GIA stating that the diamond weighing 4.03 carats is Fancy Intense Blue, natural colour, SI1 clarity. Report number 1182198420, dated 8 March 2017.

Accompanied by an additional letter from GIA stating that the diamond has been classified as Type IIb.

Accompanied by a report from GIA stating that the diamond weighing 0.63 carat is Fancy Blue, natural colour, VS1 clarity. Report number 1182305166, dated 13 April 2017.

Staying with coloured diamonds, the second headline lot is A Fancy Coloured Diamond brooch. This features a central square step-cut Fancy Gray-Blue diamond, weighing 4.83 carats, with a Fancy Dark Brown-Greenish Yellow step-cut diamond to either side, weighing 2.51 carats and 2.38 carats respectively, suspending a pear-shape Fancy Pink Diamond drop below, weighing 1.90 carats. The brooch dates from the mid-20th century and has a pre-sale estimate of £650,000-850,000. 

Lot 197. A fine fancy-coloured diamond pendent brooch. Estimate £650,000 - 850,000 (€710,000 - 920,000). Photo: Bonhams.

Note: Accompanied by a report from GIA stating that the diamond weighing 4.83 carats is Fancy Gray-Blue, natural colour, I1 clarity. Report number 5181582456, dated 20 July 2017.

Accompanied by a report from GIA stating that the diamond weighing 2.51 carats is Fancy Dark Brown-Greenish Yellow, natural colour, VS1 clarity. Report number 5181597065, dated 18 July 2017. 

Accompanied by a report from GIA stating that the diamond weighing 2.38 carats is Fancy Dark Brown-Greenish Yellow, natural colour, VS1 clarity. Report number 5181597069, dated 18 July 2017. 

Accompanied by a report from GIA stating that the diamond weighing 1.90 carats is Fancy Pink, natural colour, SI1 clarity. Report number 5182597098, dated 21 July 2017.

The third notable lot in the sale is A Kashmir sapphire single-stone ring, weighing 9.61 carats. The octagonal step-cut sapphire has no indications of heating and is estimated at £500,000–700,000.

Jean Ghika added: "Kashmir sapphires are amongst the most highly prized gems for serious collectors given the mines were only open for a period of approximately 30 years from the late 1880s onwards. This stone has the classic attributes associated with sapphires from the Kashmir region, a rich and intense blue colour coupled with a velvety appearance."

Lot 186. A fine 9.61 carats Kashmir sapphire single-stone ring, circa 1961. Estimate £650,000 - 850,000 (€710,000 - 920,000). Photo: Bonhams.

The cut-cornered step-cut sapphire, weighing 9.61 carats, between tapered baguette-cut diamond shoulders, ring size M

Note: Accompanied by a report from AGL stating that the sapphire is of Kashmir origin, with no evidence of heat or clarity enhancement. Report number 1083523, dated 12 April 2017.

Accompanied by a report from SSEF stating that the sapphire is of Kashmir origin, with no indications of heating. Report number 78392, dated 17 February 2015. 

Accompanied by a copy of the original purchase receipt from Pierre Baltensperger, dated 21 December 1961.

Bonhams will also be auctioning a number of signed pieces of jewellery by Cartier as part of its sale. These include A pair of Art Deco diamond clip brooches by Cartier, circa 1935, estimated at £40,000-60,000.

Lot 174. A pair of art deco diamond clip brooches, by Cartier, circa 1935. Estimate £40,000 - 60,000 (€43,000 - 65,000). Photo: Bonhams.

Each shield-shaped clip of geometric design, decorated with brilliant, baguette and shield-cut diamonds, mounted in platinum, signed Cartier London, maker's mark JC, diamonds approximately 16.80 carats total, lengths 3.8cm (2)

Adding a further touch of colour to the sale is An emerald and diamond bracelet by Cartier. The bracelet, which dates from the 1960s, features a series of alternating step and octagonal-cut emeralds, accented to either side by brilliant-cut diamonds and has a pre-sale estimate £50,000-70,000.

Lot 184. An Colombian emerald and diamond bracelet, by Cartier, circa 1965. Estimate £50,000 - 70,000 (€54,000 - 76,000). Photo: Bonhams.

The series of alternating step and octagonal-cut emeralds, accented to either side by brilliant-cut diamonds, diamonds approximately 2.40 carats total, signed Cartier, numbered K9506, maker's case, length 18.5cm

Note: Accompanied by a report from The Gem & Pearl Laboratory stating that two emeralds, weighing 0.81 and 0.82 carats, were tested and found to be of Colombian origin, with indications of negligible clarity enhancement. Report number 14102, dated 23rd April 2017.

For buyers who are seeking white diamonds, the sale will also feature a charming example of an old-cut diamond. The old marquise-cut diamond single-stone ring, weighing 4.61 carats, is D colour, VVS2 clarity, and potentially flawless. It is accompanied by a letter from GIA stating that the diamond is Type IIb. It has a pre-sale estimate of £80,000-100,000.

Lot 181. A 4.61 carats Type IIb diamond single-stone ring. Estimate £80,000 - 100,000 (€87,000 - 110,000). Photo: Bonhams.

The old marquise-cut diamond, weighing 4.61 carats, between shoulders decorated with single-cut diamonds, ring size M½, cased by Bentley Brothers Ltd, 76 Moorgate, London, EC2

Note: Accompanied by a report from GIA stating that the diamond is D colour, VVS2 clarity, potentially flawless. Report number 1182416344, dated 17 May 2017.

Accompanied by a letter from GIA stating that the diamond is Type IIb.

The sale will also include the largest private collection of jewels by Andrew Grima ever to appear at auction. Grima's groundbreaking designs, which drew inspiration from art, sculpture and the natural world, injected desperately needed originality and glamour into what had become a stagnant jewellery scene in post-war Britain. He created bold and unusual jewels whose value lay in their aesthetic composition rather than just in the carat weight of expensive diamonds and precious gems. He is recognised as one of the great modernist jewellery designers of the 20th century and his pieces are highly sought after worldwide.

The collection features 55 pieces of jewellery designed by Grima. Highlights include pieces from his admired "About Time" watch collection for Omega, one of the most innovative collections of watches ever made, as well as works from the "Rock Revival" collection in that incorporated large, uncut and unusual gemstone crystals.

Lot 47. A unique 18 carat gold, citrine and diamond watch-bangle, 'Cerini', No 80 from the About Time Collection, by Grima, 1969. Estimate £15,000 - 20,000 (€16,000 - 22,000). Photo: Bonhams.

The large, oval-cut citrine 'glass', within a bezel composed of a myriad of gold 'matchsticks' decorated with baguette-cut diamonds, on a wide 'matchstick' bangle, mounted in yellow gold, signed Grima, Omega mark, numbered 811924, scratched number 3255, workshop mark HJCo, London hallmark, inner diameter of bangle 5.5cm, original Grima case with tooled Omega insignia

Note: This watch was from the About Time Collection, 1970; No 80 on the original index. The design was inspired by tiny wax-coated matches - cerini - used in bars throughout Italy. It was exhibted at the Grima Retrospective, Goldsmith's Hall, May, 1991; no 254 and illustrated in Johann Willsberger's book 'Grima' in 1991.

Original sketch for lot 47 (not included) © Courtesy of Grima

Lot 44. An 18 carat gold, citrine geode and diamond 'Rock Revival' necklace, by Grima, 1971. Estimate £4,000 - 6,000 (€4,300 - 6,500). Photo: Bonhams.

The vertical knifewire pendant with a single brilliant-cut cut diamond at the top, set at intervals with four oval citrine geodes graduating in height, with textured collets to similate the 'roughness' of the natural crystals, suspended from a polished torc, mounted in yellow gold, signed Grima, workshop mark HJCo, London hallmark, pendant length 14.5cm, Grima pouch 

Exhibited: 'Grima Retrospective', May 1991 (London: Goldsmiths' Hall); No 36 in the catalogue.

The Lugano-Switzerland shop in 1991 with lot 44 on display in the cabinet. © Photo courtesy of Grima