DLC stands for Diamond-Like Carbon and denotes a surface coating of watch cases.
A surface treated in this manner is blacker than ruthenium and more abrasion resistant than PVD. The DLC coating is popular because of its hardness, the deep dark color and its hypoallergenic properties. It combines the property of carbon in its adamantine modification (extremely hard, non-conductive, chemically languid) with that of graphite (the black elastic form of carbon).
The technically sophisticated DLC is applied in several thin layers with a high-tech vacuum process. The extremely low friction coefficient and the degree of chemical inertness give it excellent resistance to scratches, abrasion and corrosion as well as flexible hardness.
Breitling refers to DLC as "Blacksteel".