Cast irons are ferrous alloys with mostly 2.5%-4% carbon and 1-3% silicon. The carbon is either present as graphite in grey irons or in form of iron carbide and alloy carbides in white cast iron. The difficulty in the metallographic preparation is to retain the true shape and size of the graphite in its flake, nodular or tempered form. During grinding the matrix is smeared over the graphite and unless it is followed by a very thorough diamond polish, the graphite is not shown in its true form. Especially cast irons with a soft ferritic matrix tend to smear and are prone to deformation and scratching. Plane grinding with silicon carbide paper is recommended, followed by fine grinding and polishing with diamond. A brief final polish with colloidal silica is optional. White cast irons are very hard and a cubic boron nitride cut-off wheel is recommended for sectioning. Note: do not use diamond cut-off wheels! Plane grinding, fine grinding and polishing are carried out with diamond. Integrated into online casting, semi-automatic preparation equipment can achieve better results for a reliable and reproducible graphite evaluation than manual preparation.