Finishes and coatings are used to prevent corrosion. The smoother the knife, the greater the corrosion resistance. Knife blade finishes can be achieved by use of titanium nitride, satin finish, mirror polish, bead blasting and black oxide painting. Titanium Nitride (TiNi) is the best coating that can be applied to steel, it is commonly used for black finishes and to increase the durability of the knife. The TiNi finish is extremely scratch and peel resistant and is applied to steel through a unique process of plasma deposition performed in a complete air-sealed vacuum.
A Satin finish is a semi-shiny finish with a luster falling between bead blasted (matte) and mirror polish (high gloss). It is the most popular and typical finish on production of knife blades and it shows fine buffing lines with two directional finishes that give a better display of the bevels of the blade. It has decent corrosion resistance, but less than polish or mirror finished knives.
A Mirror Polish is a highly reflective finish typically seen only on high-end, custom, and handmade knives. It reflects like a mirror and is one of the most expensive knife finishes. It has high polish and smoothness, which make it corrosion resistant.
Bead Blasting is a non-reflective finish created by blasting the surface of a blade with various media such as beads or sand, which produce a rough surface more prone to surface corrosion. This looks great on tactical, combat, or fighting knives where reflection of a shiny blade is unwanted. It also compliments a knife blade that will then be hot blued, for a completely flat black finish.
Black Oxide, or blackening, is a conversion coating for ferrous materials that is used to add mild corrosion resistance and for an appealing black appearance. Black Paint, or powder coating, is the lowest quality blade coating. The paint gives the blade low reflectivity but has a high probability of scratching. A polished finish is similar to a mirror finish, but it is less reflective. It has great corrosion resistance and shows scratches easily. The stonewash finish involves having the steel rolled with pebbles and then smoothed. It hides scratches better than other finishes.
Coatings provide corrosion resistance, but they will scratch off eventually and at different rates, depending on the quality of the coating. Black, powder coatings, and titanium nitride are a few coatings that are available. DLC (Diamond-like-carbon) is one of the best black coatings and it will hold up longer than most other coatings. Coatings are not shiny.
Finishes and coatings will wear away with use over time. To prevent rust from accumulating, the knife blades should be cleaned, dried, and oiled on a regular basis.