Black oxide

Modern industrial approaches to forming black oxide include the hot and mid-temperature processes described below.

They are of interest historically, and are also useful for hobbyists to form black oxide safely with little equipment and without toxic chemicals.

These tanks contain, in order, alkaline detergent, water, sodium hydroxide at 140.5 °C (284.9 °F) (the blackening compound), and finally the sealant, which is usually oil.

There are many advantages of blackening, including: The oldest and most widely used specification for hot black oxide is MIL-DTL-13924, which covers four classes of processes for different substrates.

This coating produces a similar color to the one the oxide conversion does, but tends to rub off easily and offers less abrasion resistance.

The application of oil, wax, or lacquer brings the corrosion resistance up to par with the hot and mid-temperature.

Applications for cold black oxide process include tooling and architectural finishing on steel.

[8] On a microscopic scale dendrites form on the surface finish, which trap light and increase absorptivity.

[8] In printed circuit boards (PCBs), the use of black oxide provides better adhesion for the fiberglass laminate layers.

Black oxide finish is used on surgical instruments in light-intensive environments to reduce eye fatigue.

[citation needed] Room-temperature blackening for stainless steel occurs by auto-catalytic reaction of copper-selenide depositing on the stainless-steel surface.