From outside to inside the scales excist of three layers:

1. The cosmine layer, a thin layer of enamel and a layer of dentin.
2.  The vascular layer with big canals and pores.
3.  The isopedine lamilar layer with growth zones

The normal photomicrographs do not show much of the individual growth zones but when looked through a polarising microscope with the help of crossed nicols the growth zones show as light and dark bands.

With crosssed nicols and a retardation plate the different growth zones get a color and the enamel layer, the thin layer on top of the scale, depending on the direction of the slide under the crossed nicols becomes orange or blue.