Unlock the mysteries of your jewel box

What are the differences between natural sapphires, emeralds, rubies and pearls, and those that have been treated or cultivated? Specialist Jessica Peshall explains how an expert eye can help reveal the true nature of the jewels in your collection

  • 1
  • The origins of a sapphire

A sapphire and diamond ring. 10.27 carats, Sri Lanka. Sold for $50,000 on 18 September 2016 at Christie’s in New York     

A sapphire and diamond ring. 10.27 carats, Sri Lanka. Sold for $50,000 on 18 September 2016 at Christie’s in New York     

A sapphire and diamond ring, by Gübelin. 10.50 carats, Kashmir. Sold for $305,000 on 10 December 2015 at Christie’s in New York       

A sapphire and diamond ring, by Gübelin. 10.50 carats, Kashmir. Sold for $305,000 on 10 December 2015 at Christie’s in New York       

To the untrained eye these two sapphires may at first appear similar. They are of comparable size, cut and hue, but one surpasses the other many times in terms of value.

The three most important geographical locations for sapphires, in order of the premiums their origins command, are Kashmir, Burma and Sri Lanka. 

The example on the left, set with an attractive sapphire of Sri Lankan origin, exhibits a well-saturated, bright, clean appearance and sold for $50,000 at auction. 

The sapphire on the right, however, originates from Kashmir, where the famed gem mines once produced what are now the most highly sought-after sapphires in the world. They are renowned for their vivid, rich, blue saturation and, most importantly, a characteristic and elusive subdued velvety texture that seems to make the gem glow from within. This Kashmir sapphire sold for $305,000 at auction.

 

  • 2
  • Cultured pearls versus natural pearls

A pair of cultured pearl and diamond earrings. Sold for £1,750 on 21 January 2015 at Christie’s South Kensington 

A pair of cultured pearl and diamond earrings. Sold for £1,750 on 21 January 2015 at Christie’s South Kensington 

A pair of Belle Epoque natural pearl and diamond ear pendants. Sold for £60,000 on 30 November 2016 at Christie’s London 

A pair of Belle Epoque natural pearl and diamond ear pendants. Sold for £60,000 on 30 November 2016 at Christie’s London 

Throughout history natural pearls have been the favoured gemstone of kings, emperors, maharajas and the affluent as a means to display their wealth and influence. Many early portraits depict sovereigns resplendently swathed in strings of these highly precious, pale, glimmering spheres. 

It is said that for every 10,000 wild oysters that are opened only one natural pearl is found, and only a small fraction of these pearls are of gem quality, which attests unequivocally to their rarity.

It was in the early 20th century when, after many years of research and numerous failed attempts, the first harvest of gem-quality cultured pearls was collected. 

Despite fluctuations in the market due to the introduction of their cultured counterparts, natural pearls remain highly sought-after, and exceed their man-made equivalents many times over in terms of value. The example depicted above left, a pair of cultured pearl ear pendants, sold for £1,750 at auction. However, the pair of natural pearl ear pendants on the right sold for £60,000.

 

  • 3
  • The value of untreated emeralds

An emerald and diamond ring. 4.06 carats, Colombia. Significant clarity enhancement. Sold for £13,750 on 2 December 2015 at Christie’s London

An emerald and diamond ring. 4.06 carats, Colombia. Significant clarity enhancement. Sold for £13,750 on 2 December 2015 at Christie’s London

A three-stone emerald and diamond ring, by Carvin French. 4.42 carats, Colombia. No clarity enhancement. Sold for $293,000 on 10 December 2015 at Christie’s in New York

A three-stone emerald and diamond ring, by Carvin French. 4.42 carats, Colombia. No clarity enhancement. Sold for $293,000 on 10 December 2015 at Christie’s in New York

Emeralds have been associated with royalty and splendour since the age of Cleopatra. They belong to the beryl species of gemstone — which also includes aquamarine and morganite — and very often contain internal features such as veils and wisps of natural imperfections. These features have been romantically termed ‘jardin’, since they bring to mind gazing into an overgrown, verdant garden. 

For centuries emeralds have been treated with oil to help conceal these features. Encountering an emerald with few or no visible inclusions, paired with minor or negligible levels of oil, is an absolute rarity. Clean crystals of this vivid green gem are thus highly prized among collectors and connoisseurs.

While there is certainly a market for attractive emeralds that have been treated with oil — for example the emerald ring on the left, which sold for just under $21,000 in December 2015 — pure, untreated examples can fetch astounding sums. The example pictured on the right was sold eight days later for $293,000.

 

  • 4
  • Rubies — heated or natural?

A ruby and diamond ring. 7.19 carats, Burma. Heated. Sold for $317,000 on 10 November 2015 at Christie’s in Geneva

A ruby and diamond ring. 7.19 carats, Burma. Heated. Sold for $317,000 on 10 November 2015 at Christie’s in Geneva

A ruby and diamond ring. 7.77 carats, Burma. Unheated. Sold for $1,760,000 on 15 November 2016 at Christie’s in Geneva

A ruby and diamond ring. 7.77 carats, Burma. Unheated. Sold for $1,760,000 on 15 November 2016 at Christie’s in Geneva

Known as the King of Gems, the ruby is perhaps the rarest and most precious of all the coloured gemstones. Belonging to the corundum mineral species — which also includes sapphires — these gems are colourless in their purest form. Rich pinkish reds and deep crimson hues are caused by the presence of traces of chromium within the crystal structure.

In the course of the 19th century it was discovered that these colourless stones could be transformed into vividly coloured rubies by heating them in the presence of chromium. This treatment has become quite commonplace, and ‘heated’ rubies are now widely accepted in today’s market. 

Jewels set with heat-treated rubies are much more affordable compared to their naturally coloured counterparts. Unheated rubies boasting a rich colour and good level of clarity are very rare, highly precious and often fetch remarkable sums at auction. The heated ruby ring pictured above left sold for $317,000, whereas the comparable unheated example sold for $1,760,000.


 

A Christie’s specialist can help you to discover the nature and origin of your jewels by identifying the tell-tale signs that reveal a gem’s provenance and true value. Find out when the next Christie’s valuation day is taking place near you.