In the last 70 years the increase in value for investment diamonds has been between 4-8% annually.
DE BEERS has been able to develop a safe system that guarantees a continuous increase in price, as it has been in this past Century. There are no imaginable causes that might, in the future, break this continuity.
Example: Diamond Colour River D, Clarity IF (absolutely pure with no inclusions when magnified by 10), Cut vg vg (very good, very good), of 1 Carat. Acquired in 1990 at US $ 34.900 (at the value of US $ 349 per carat point). Sold in 2000 at US $ 59.000 (at the value of US $ 595 per carat point) with a net profit of 70%.