Mining and smuggling in Sierra is easy and cheap

Gems' provenance - where they were purchased from - is documented, but where they are mined is often unknown.

There is no reliable method of identifying the characteristics of a single diamond, without damaging it.

Meanwhile, prices soar as gems proceed along the pipeline, with $6.8 billion annual international production of uncut stones being turned into 67 million pieces of jewellery worth $50 billion.

With such potential for enrichment - in an industry renowned for secrecy - the words "ethical" and "diamonds" have seldom been used together.

Blood diamonds

Campaigns against "conflict diamonds" or "blood diamonds" have successfully raised public awareness in the capability of diamond smuggling to provide the finance and indeed the motive for vicious civil wars.

Fearing they might find themselves in a similar position to the fur trade, a luxury product stained by blood in the minds of consumers, the big players in the diamond industry have recently responded by promoting "ethical diamonds".

A glamorous image could be tainted by conflict

Diamonds are a low mass, high-value commodity. Tighter controls here mean smuggled stones will pop out somewhere else.

Liberia, a "flag of convenience" for trade in a number of more or less dubious sources of diamonds - including Sierra Leone - is an obvious target for a wider embargo.

But how to stop the shady arms-for-diamonds dealers who arrive in West Africa from who-knows-where and fly off again when their deals are done?

De Beers' answer focuses on the cutting stage of the pipeline.

If the main cutting centres in Belgium, Israel, India and the US could be obliged only to accept diamonds of clear origin, conflict diamonds could be squeezed out of the industry.

But with millions of dollars to be made, there is no sign of that happening yet.