Color etchant according to BERAHA II is primarily used for metallography and finds application in scientific laboratories. It is used in particular for high-alloy steels such as austenitic CrNi steels. In this product category, it is suitable for coloring delta ferrite and austenite, while the sigma phase remains white.

The kit is composed of ammonium hydrogen difluoride (NH4HF2), potassium disulfite (K2S2O5) and 12% hydrochloric acid (HCl). Ammonium hydrogen difluoride reacts with the hydrochloric acid to form hydrogen fluoride (HF) and the NH4+ ions. In the process, potassium disulfite provides for the reduction of iron and chromium oxides on the surface of the austenitic steels, resulting in increased selectivity of the coloring.

The chemical reaction between these components results in the formation of a solution that is both corrosive and coloring. Once prepared, the solution is usually stable for 1-2 hours. Wet etching at a duration of 10 to 20 seconds can selectively color the desired areas on the steel surface.

Due to the corrosive properties of the product, it is recommended that the stock solution be stored in a plastic bottle, as glass could be attacked. The main field of application of color etchant according to BERAHA II is the selective coloring of austenitic steels in metallography.