Can we know where a diamond has come from?

Lets look at the evidence we have so far. We know that diamonds contain small amounts of other substances, known as impurities, which can give them color. Special optical techniques can be used to determine what the impurities are. These impurities give a possible start to tracing diamonds. For example, it is thought that Sierra Leone has a distinctive profile of sulfides (sulfur-containing molecules). Unfortunately, these tests have not been carried out routinely by all of the diamond producing countries of the world. To get this sort of information a lot of research would have to be done by testing diamonds from every mine. One of the major pitfalls of this type of identification is that all diamond is formed in the molten rock of the mantel. Rather like a pan of water being heated, the mantel has very slow convection currents that keep it flowing and mixed up. Due to these currents, the chemical content of the mantel is thought to be similar everywhere around the globe. It is therefore likely that, even though diamonds are mined at many different parts of the earth's surface, the impurities in them will be very similar. In fact it has been found that is virtually impossible to distinguish between rough diamonds from conflict zones and those mined legitimately in countries such as Botswana, the biggest rough diamond producer in the world.
So are there other methods of identification? Scientists have looked at uncut unpolished diamonds from different regions of the world and they have found that their size, shape and surface roughness can be a key to where they come from. However, when lots of diamonds are mixed together from a number of different sources it is still very difficult to separate them out in to their different regions, because the differences between them are too small. It becomes even harder once they are cut and polished, as all these original features are removed.
Rain may be the key to identifying the origins of rough diamonds. When it soaks in to the ground it comes into contact with the diamonds. It can leave hydrogen atoms or isotopes on the surface of the gems that are unique to the rain water in that region. These atoms or isotopes are held very strongly on the surface so are not easily removed.
All of these techniques seem straightforward, but they do not work all of the time, so at present, all countries that produce diamonds legally have signed an agreement that they will not buy conflict diamonds and that they will keep records of each diamond that comes out of every mine. Every stone is marked and cataloged through out its life and its documents (or 'certificate of origin') travel with it. Using techniques such as branding this should be possible, but wouldn't it be much easier if a technique could be developed like the one James's scientist had in the film. Well, maybe it has! In June 2002, a company reported that it had developed such a machine that can be used on rough and cut diamond. It is not yet in operation but hopefully will be soon. The manufacturers say that it is like a photocopying machine - put a rough diamond in to it and it identifies all its unique characteristics, its origin and its value, then forms a blueprint of the diamond and keeps it on record, then it brands the diamond. The cost of this machine is thought to be about $1 million - not very much if you compare it to the profits made every year by the diamond industry.