| Here is a good one for Zeide to sink her teeth into,
had a call yesterday from a gemologist. he wanted to talk about the distinction between orient and overtone. As I recall the GIA definition, orient is defined as a rainbow effect, that is polychromatic whereas overtone is monochromatic this has me confused.
Fine black pearls will often exhibit a monochromatic overtone, pink, green, blue. Occasionally the overtone is mottled, that is you might see pink on one side, green on the other.
The only time I have seen a true rainbow affect is in very baroque Chinese pearls. Occasionally white southsea will exhibit a bit of pink. I have assumed that this was a result of light interference, that is, light beams bouncing off various hills and valleys in the pearl and knocking into one another. Overtone on the other hand is mainly the result of light diffraction through a grid created by the alignment of aragonite crystals Am I missing something? |