Given that one carat near colourless stones were selling at around pounds 2000 at Sotheby's in April even a

Given that one carat near colourless stones were selling at around pounds 2,000 at Sotheby's in April, even a DIY approach does not come cheap.However, at the end of the day, one will have a jewel that will mean far more to both the giver and the wearer than a similar piece just selected from a jeweller's stock. So, would it not be better to buy a cut stone and have a ring made? While perfectly possible, Andy Bone at De Beers admits that it is difficult for the public to buy an unmounted stone in Hatton Garden.Although the supply and demand of rough diamonds is controlled, the price to the consumer is not. It is a well-known fact that the mark-up of high street jewellers is one of the highest of retailers. But there are good reasons for this, the main one being the high value of stocks they have to hold to give their customers a choice.

However, it is the inter-relationship of the 4C's that determines a diamond's value. A flawless, colourless one carat stone of good cut will be worth more than one which is twice the size but is near colourless with very minor inclusions.If you want to buy a single diamond, the jeweller is still the best bet. If a diamond is cut too deep or too shallow, light escapes through the bottom of the stone.Finally there is size - 95 per cent of all cut diamonds weigh less than a carat. Minor inclusions, which are still difficult to see with the untrained eye, are referred to as VS1 and VS2; noticeable inclusions which are easy or very easy to see with a 10x lens are S11 and S12, whereas those with obvious inclusions are 11, 12 and 13.The precision and delicacy of the cut dictates the maximum amount of light that will be reflected through the diamond. When the stone is cut to good proportions, light is reflected from one facet to another and dispersed through the top of the stone. The most sought-after colour for a diamond is one where there is no colour at all.Clarity relates to the impurities in a diamond The more impurities, the lower its price per carat.

An internally flawless stone is known as "IF", whereas those with only very slight inclusions, which can only be seen with difficulty from the back of the stone using a 10x magnifying glass, are known as VVS1 and VVS2. Bargaining is only allowed for individual stones in excess of 10 carats.Rough diamonds may not be an investment, but, how does one go about getting value for money on cut stones? The question may appear straightforward, but the answer is complex. As De Beers states in its excellent leaflet, Quality and Value, which is available from all good jewellers or direct from the CSO, "There's more to diamonds than meets the eye."The characteristics that determine the quality of a diamond are known as the 4C's: colour, clarity, cut and carat, which is the stone's weight. There they are sorted into over 5,000 categories of number of shape, quality, colour and size. Even if obtainable, such a vast number of categories is a good reason for not even contemplating buying uncut stones.Once sorted, the diamonds are blended into a "selling mixture" in preparation for the 10 annual "sights" in London, at which the rough stones are sold to some 160 clients of the CSO The mixtures are offered at a non-negotiable price. If this happened, the price of diamonds could have plummeted. However, although the Russians desperately need hard currency, they are hardly likely to shoot themselves in the foot.The rough diamonds from the big producing nations that belong to the CSO go to its London offices.