The colour of pearl (body colour) depends on the organic matter which lies between the pearl layer and the nucleus. Overrating of chemical analysis brought forth the erroneous conception that the luster is caused by pigments contained in the pearl layer. A device has been made to determine the body colour and the surface colour separately. When a pearl is cut in two and the nucleus and organic matter removed, the remaining shell layer, whether originally yellow, blue or green, appears light orange and gives a spectrophotometric curve of permeation common to all pearls. However, when seen with naked eye, it may appear green, purple, red or else by the scattering of light. By attaching a suitable substance to the inside of the shell, any desired body colour can be realized which would open up the way of controlling the colour of cultured pearls.
