I found good information on www.bluenile.com/education/diamonds They explain the 4Cs - cut, color, clarity, and carat weight - the most important characteristics to take into account when buying diamonds. There’s a short tutorial too =)
Probably the best way for you to decide where to invest will be based on the budget you have. Within this budget you can decide (might be even wiser) whether to split it into 5 x £5,000 diamonds or to buy one £25,000 diamond etc.
In my opinion, diamonds must meet the following characteristics to be considered as good investments.
- Carat: Between 1 ct and 6 ct (from the point of view of the investment, not recommended more carat).
- Purity: superior to VS2, up to Loupe Clean.
- Color: D, E or F in white diamonds Diamonds with an intense natural coloration (for example blue, yellow, pink, red), as long as it exists on demand.
If you are absolutely keen on buying diamonds and your objective is to get profits you should buy diamonds one carat and above. Smaller diamonds are unlikely to fetch worthwhile prices. Naturally colored diamonds are very rare, more rare than colorless diamonds. Only 1 in 10,000 diamonds has a natural color and is therefore called a "Fancy" diamond. The intensity of the color, that is, the depth or the vividness of the color, is the most important parameter in the purchase of a "Fancy" colored diamond. The more intense the color, the more rare and valuable the diamond will be.