Martin Rees, Jeweller and Pawnbroker


A good quality diamond seen through the microscope


Brief facts

Diamonds are crystalised carbon.

Graphite (the lead in pencils) is also crystalised carbon, but a different crystal form.

Diamonds will burn (please don't try this at home!)

A diamond was believed to protect the wearer from the Devil, as well as the Plague.

Diamonds are very hard, but like many other gemstones they are somewhat brittle, so a violent blow can crack or chip the stone.  We see many old rings, and often the diamonds are damaged.

Note the different colours as the light is refracted in the above stone,  because the crystal breaks up light like a prism (this colour effect is called fire).  Also you can see various fractures and inclusions, most in the top left of the stone.  Just one is clearly visible near the centre, but good cutting means most are towards the edge. Click here for larger image (222KB).

Over 120 miles (200km) below the earth's surface and upto 3 billion years ago, temperatures of 1100C and the incredible pressure of 65,000 atmospheres allowed diamonds to form.  Aeons later, rocks like Kimberlite transported these precious stones towards the surface.
Diamonds are (as we all know) the hardest natural substance, so can be used for cutting any material;  they were used to cut the intricate marble designs on the Taj Mahal.
When I first became interested in jewellery, I did not appreciate diamonds.  However admiring their beauty under the microscope, and seeing these various inclusions and the beauty of their crystal structure has resulted in my coming to regard them among the very best of gems.

Cutting and Shaping Diamonds

An uncut diamond, as it comes from the mine

This is the starting point: a diamond fresh from the ground. The small triangles are the crystal facets. This diamond won't be cut for jewellery, it has too many flaws and inclusions. Click here for larger image (169KB).

Their hardness makes cutting the facets, which cause the sparkle and fire, very difficult.  Faceted stones have only been around a few hundred years.  Finally in 1919 scientists worked out how to maximise the sparkle and fire by cutting the facets at the perfect antle.
Diamonds can only be cut or polished by another diamond.  This works because diamonds are harder at some angles than others - a result of the crystal structure.  Before cutting, the craftsman will ensure that no facets lie along this line of maximum hardness - because these would be impossible to cut or polish.  Provided that particular angle is avoided some of the diamond dust used for cutting and polishing will be harder than the diamond which is being worked on.
Diamonds may look clear but actually they have varying tints from blue white towards brown.  Blue white commands the highest price. Coloured stones do occur, and if attractive are very valuable.  Most diamonds are too flawed to be worn as jewellery and are used in industry for cutting and grinding.

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Inclusions and Flaws

Many fascinating inclusions are found in diamonds, including garnet crystals.  The clarity of the diamond means these inclusions really look superb.  Sadly the most common are dull black spots, often called carbon, but more often actually sulphide as in the picture below.
diamond with interesting black inclusion This is a rather attractive black spot, which I call 'The bee.'  Luckily it's so small it doesn't spoil this stone.  Many diamonds have larger black inclusions (and less fascinating shapes), which reduce the stone's value.  Fractures are also common;  if they are small, the stone is not weakened.
In the best stones flaws are only visible through a powerful lens, in cheap stones you will see them with the naked eye.  So the price for a blue white stone which looks clear to the naked eye will be many times more than the price for a yellowish stone with black spots!

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Cleaning diamonds

Cleaning is simple - they won't be affected by hot water.  Make sure the back of the stones is kept clean, use a proprietary jewellery cleaner or a detergent, but not soap - diamonds attract grease and fats, and most soap contains some fat.  While you can clean the stone for yourself, we recommend you get a jeweller to clean and examine your diamond jewellery every year.  Replacing a diamond is expensive, so it makes sense to have your jewellery checked to ensure the stones are secure.

Treated Stones

Almost all diamonds are sold in their natural state.  But diamonds can be 'clarity enhanced' by filling a fracture to conceal it.  Also black spots can be removed by using a laser to drill into them, then bleaching the mark.  However these treatments may not be permanent.  Fracture filling can deteriorate with time, and repairers have encountered problems with laser-drilled stones.  Stones can be 'colour enhanced' by coating with a substance which hides an unacceptable colour tint.  The treatment is not permanent.
You can buy with confidence in the UK, because the law requires that you are notified before purchase of any such treatment.  As a result, few 'enhanced' diamonds are sold;  but it is wise to buy from reputable dealers.

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How much is a diamond worth

Price depends on many factors.
First there is the weight, larger stones are [obviously] worth more.  But quality is even more important than weight.
Inclusions can really spoil a large stone and make it look dull.  What about the cutting of the facets?  If the angles are wrong, much less light will be refracted within the stone, and it will have less fire.
Finally consider the colour.  Some stones look yellowish when compared to good diamonds.  They look disappointing, and that will bring their value down a lot.
But the final test is your judgement.  Two stones may seem identical when described, yet one could be much more appealing when seen, and that is the one which is worth more to you.  And that is why it's so wise to view a diamond before buying.  If you are viewing stones in different shops, take along a diamond (perhaps in a ring) or CZ and compare the gems which interest you to that reference stone.  That will help you make allowance for different lighting etc in the shops.

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