This is a tentative to make a pearl material.

Natural pearl material are made of hundreds of quasi-periodic thin film structure. They are translucent and feature interference effects in the volume.

Faked pearl-looking materials are plain translucent materials (such as milky plastic or glass) with a thin film coating (high index material) having non-uniform thickness. Therefore, the interference is only surfacic, causing part of the fake look.

As it is not possible to make volumic interferences in Indigo, I made a material which is physically quite close to the industrial fake version. The inner material is regular milky SSS, and the surface is a thin-film computed by a spectral shader. It's not 100% correct as I cannot put an angle dependant blend shader (thus the transmission coefficient is constant where it should have been 1-R)

Rendering this material is very slow due to SSS

Enjoy,

Etienne