Video S1 - polarimetry of shell as a function of horizontal position

Polarimetry imaging of the Pinctada fucata shell as the shell was moved horizontally through the beam, thereby illuminating nacre, myostracal layer, nacre, and prismatic layer, in order, shows distinct light transmission patterns for each region. The sample was moved horizontally through the beam with the movie beginning with imaging the light before it is transmitted through the shell, followed by imaging the light as it is transmitted first through the nacre, then the myostracal layer, the nacre between the myostracal layer and the prismatic layer, and finally the prismatic layer. The regions of low intensity within the images are indicative of regions of the sample where the transmitted light did not match the selected polarization filter, which was held constant throughout the movie. As can be seen within the movie, there are repeating fringes of high and low intensity with varying periodicity in both nacre regions.