Blade Coating.

Added layer or worked surface

A knife spec sheet can print PVD coated on one knife and stonewash finish on the next without explaining the difference. A finish such as stonewash or bead blast applies nothing: the steel's own surface is scuffed or blasted. A coating puts a layer on top.

The labels are loose. Boker calls PVD coating a finishing method, Kershaw calls its BlackWash, which may be DLC or black-oxide based, a finish, and the Hogue Extrak in the grid below prints Cerakote finish. Judge by the mechanism, not the label.

Each coating, as its maker describes it

• Black oxide: Kershaw says a chemical bath converts the surface to magnetite, which enhances appearance and "adds some corrosion resistance." Gerber says it applies black oxide to specific knives for ornamental reasons.
• PVD: Kershaw says specialized materials are vaporized in a vacuum and deposited as a thin layer, which on its blades and handles "offers excellent wear and corrosion resistance."
• Titanium aluminum nitride: Boker calls it a type of PVD coating, 0.5 to 3 µm thick overall.
• DLC: Kershaw says Diamond-Like Carbon coating "displays properties similar to those of natural diamond, including hardness, wear resistance, and reduced friction."
• Powder coat: Kershaw says it is applied as a fine powder and cured under heat.
• Cerakote: Kershaw calls it a durable polymer-ceramic composite coating in a variety of colors.

Hardness claimed for a coating belongs to that surface layer; the steel's own hardness is set by its alloy and heat treatment, and the Steel Lab profiles the alloy.

Wear, sharpening and recoating

Kershaw says of its own coatings that "in time, all coatings will show some wear", and Gerber says rubbing on a sheath or pants pocket will wear its black Teflon or black oxide coatings through over time.

Sharpening removes steel at the edge and any coating on it, so a freshly sharpened coated blade shows bare steel along the edge. Kershaw says it cannot recoat a blade, even for a fee.