The D12 is an oval shaped, fine diamond sharpening steel, ideal for kitchen knives. To ensure a long steel life the surface has been coated with titanium alumina nitrid, which is an extremely hard material. The C12 steel is ceramic and is used after the diamond steel to obtain a long-term edge. This brand new ceramic steel is made of real ceramic and has got micro-grooves along the entire surface. These grooves will polish the to razor sharpness and clean off the unstable raw edge, making it last longer.