How to properly blacken and rust protect steel chain?

Question

I am working on a project where I need to blacken some steel components to a matched finish, including a length of steel chain. I am using Jax Iron, Steel and Nickle Blackener: https://jaxchemical.com/shop/jax-iron-steel-nickel-blackener/

Usually with this product I follow up with a Rustoleum spray on enamel coat to prevent rust immediately after drying from the blackening process. This has always worked well for me. However I am wondering if this is feasible for chain, since the proximity of the links will prevent the enamel from reaching all surfaces, and the friction between the links when moving seems like it would take the enamel off.

How should I go about rust proofing the length of chain?

Answer 1

You are right about the enamel being stripped between the links. The high point pressure would abrade the protective coating quickly.

Painted on chemical oxide finishes are extremely thin. The alternative industrial bluing processes utilise corrosive chemicals (see Professional Metal Re-Finishing And Hot Caustic Bluing and Amateur Gunsmithing, pgs 74-77) and are not much fun in a non-commercial setting.

If you sandblast your parts and etch them briefly in acid before bluing them, and then oil them afterward to protect the new finish, the roughness created by the preparation may be adequate to prevent the rubbing from shining up the parts during use. The oil prevents further corrosion from changing the colour.

Your problem was faced in medieval times by knights' squires who were responsible for maintaining chain mail. There has been much written about how mail tumbled in coarse sand would become suitably polished suggesting the need for frequent treatment to prevent rust for anything with frequent movement.