Let's look at a magnified section of a pearl layer and see how it is constructed. A pearl layer is composed of stratified calcium crystals. The thickness of one calcium crystal is about 0.4 micron(1 micron = one thousandth of a mm). So, a 1mm pearl layer has as many as 2500 thin films of calcium crystals. When light reaches the surface of the pearl layer, a phenomenon called "interference in many thin films"occurs in the translucent layer and a beautiful rainbow color appears on the surface. The protein between calcium crystals which glues the crystals together sometimes contains pigments(yellow pigment in Akoya pearl oysters, brown pigment in black lip pearl shells). When pigments accumulate, they determine the colors of the pearls, for example, the golden pearls or black pearls from black lip pearl shells. Sometimes organic substances have accumulated in the pearl sack before its cells secrete nacre. The accumulated organic substances have accumulated in the pearl sack before its cells secrete nacre. The accumulated organic substances at the bottom of the pearl layer result in a blue color. In effect, these three factors; 1.light interference 2.pigments 3.organic substances interact intimately with each other to determine a pearl's color. The final results are pearls of over 20 different colors.
					If you observe the surface of a pearl with a lens of low magnification, you will see patterns similar to finger prints. These patterns represent the growth of a pearl layer. Further magnification makes it possible to see the hexagonal crystals.