Examination of human fingernail ridges by means of polarized light

A method has been developed for the preparation of thin human nail specimens suitable for examination by transmitted light microscopy. The nails to be examined are embedded in an acrylic resin and the upper surface of the nail is sanded and polished until the desired thickness is reached. The resulting thin nail specimens display sharp bands of interference colors when placed between crossed polarizing filters. The widths of the bands are of the same order of magnitude as the widths of the ridges and valleys on the nail surface, indicating that each band of color represents a single ridge or valley on the nail surface. The optimum viewing conditions are obtained when the specimens are oriented so that the direction of the nail ridges is 45 deg from the directions of the polarizing or analyzing filters. Fingernail specimens from the same finger may be matched by using a transmitted light comparison microscope equipped for polarized light observations.