Using Nital (2-3% nitric acid in ethanol) to reveal steel microstructure. Loosen cotton swab tip, etch for 30-45 seconds to yield a visibly cloudy surface, dunk in water to stop etch, place swab in baking soda dish and cap acid container. Etching is a controlled corrosion reaction used to attack the chemically active areas like grain boundaries where the misalignment of atoms gives them higher surface energy. There may also be composition differences at grain boundaries or within certain phases which also enables preferred/accelerated corrosion at these locations.

Etching recipes starting on pg 77: https://www.buehler.com/assets/3DISSU...

Reference: https://vector.cnam.umd.edu/images/li...