Meesh, could you please explain exactly what strong fluorescence is. I always thought that a diamond with fluorescence went cloudy in sunlight, but from what you say I think I must be wrong. Is it true that stones with fluorescence are more popular in the US? Thanks in advance for putting your teaching hat on once again!
It's a common misconception that fluorescence = milky/cloudy/oily looking diamonds. In fact, fluoresence like that only happens once in a million stones! I absolutely adore fluorescence because it gives diamonds a blue/white appearance. Years ago, blue/white diamonds were highly prized and sought after. There's now a resurgence towards fluorescence but not necessarily in the States. Actually very few people understand fluor and tend to make the same assumption as you that fluor = yuck! I belong to a diamond junkie forum and it's amazing how many people say "I'm looking for a diamond but don't want fluor". They are then shown pictures and go "oh, okay maybe I should look at fluor and not discount it!".
I'm going to give you an example of a ring I have. This is an I colour (GIA graded) with strong blue fluor. The effect of the fluor is that the blue negates any yellow you might see, so you end up with a diamond that looks much much whiter than it actually is. In sunlight, the diamond has blue and violet tones dancing off it which is very attractive. You can also sometimes see blue tones during normal light but not really in the UK where the strength of day to day UV differs.
Fluor in coloured gemstones (including coloured diamonds) can make a gem appear very different from the "norm". For example, I have a Padparadscha Sapphire with strong red fluor that gives the effect of being a colour change gemstone because the fluor reacts to the amount of UV light. So, whereas a normal Pad with no fluor would look a peach/pink colour all of the time, mine looks very pink/very peach/very mixed! So in effect the fluor pronounces the colours I see.
There are also different colours of fluor i.e. yellow, blue, green, red, orange etc. My chameleon diamond has strong yellow fluor, and I have a blue diamond that fluoresces red! There are also degrees of fluor i.e. strong, medium, faint etc.
Luckily, in the diamond world, the prices of diamonds with strong fluor are still kept lower (although I suspect this won't be the case for long) so if you're looking for a great deal, move down the colour range and look for fluor (strong or medium).
