I have to agree that for most part it's experience. "Once you see it, you know it" kind of thing but rather difficult to explain but I'll try...
These are for commercially available pearls and what's typical in the market.
South Sea pearls
Size: 8mm up (Most available at 10-12mm if you are buying loose pearls)
Color: White, cream, golden
Overtones: silver, green, blue, rose (silver is common, rose not much, if there is no overtone.. it's ivory, which is most common)
Tahitian pearls
Size: 8mm up (Most available at 10-12mm if you are buying loose pearls)
Color, Usually different shades of gray
Overtones: Peacock, Silver, Aubergine (a lot are those steel gray types)
Luster: Satiny, can be metallic if in peacock
Akoya pearls
Size: 6mm-8mm is most usual
Color: White, cream, dyed golden and black
Overtones: silver, rose
Luster: Sharp
Freshwater pearls
Size: 2mm up (most commonly available are 4-10mm)
Color: White, lavender, peach, dyed black, cream
Overtones: silver, rose, green, cream-rose, rainbow
Luster: If it's silver, it can be sharp.. esp. for peaches and lavenders. Whites have ivory or rose or cream-rose.
Tahitian vs. Dyed FWPs
- dyed fwps usually have dye marks and most surface are not smooth (as a lot of low quality pearls are dyed black.
- peacock color is prized in tahitians but most are usually steel gray and can be dull, while the dyed black fwps have strong peocock colors, some tend to go bronze.
South Sea vs. FWPs
- Look at the drillhole for signs of a nucleus.
- South seas are usually round, a high button, baroque, and oval. A big oblong strand of pearls and most likely fwps as there's not much south sea of this shape but lots in fwps. A baroque with a flat side is most likely to occur in fwps, but not much in south seas.
- A very low button pearl is most likely fwp.
- A bit of a tail (not fireball, but like the tip of a vase or bottle) occurs in South Seas and Tahitians, sometime with a bit of discoloration. Haven't seen this tail in fwps.
- Dull spots are common in fwps, and since there are very few big fwps (11mm up), most have dull spots. Dull spots are not as common in South Seas. South seas usually have a luster (or the lack of it) that is evenly distributed.
- Orient seldom occurs in South seas but more possibly in fwps (orient is South Seas are priced highly).
Akoyas vs. FWPs
- Look at the drillhole for signs of a nucleus.
- Look for blinking in Akoyas when you rotate the strand. A high quality strand available commercially will have one or two blinking pearls.
- Akoyas luster is sharp, and orient seldom occurs in akoyas. Fwps have a glow or deep luster.
- Akoyas usually have bumps while fwps usually have pits.
