The KLEMM-I Etching kit consists of the KLEMM stock solution and potassium disulfite and is used as an etchant in laboratory environments. It shows its strength especially in the etching of unalloyed and low-alloyed steels, cast iron, manganese steel, pure zinc and low-alloyed zinc. It is also used for segregation etching and for the detection of cementite. The unique chemical composition of the kit enables an effective etching reaction, with potassium disulfite acting as a reducing agent. After the application of KLEMM-I etching, characteristic microstructures can be visualized in the treated materials. The etching time varies between 1-2 minutes depending on the material, and about 5 minutes for cast iron. It should be noted that the etchant itself has a shelf life of only 1-2 days, while the stock solution has an unlimited shelf life.