Maglight/Simichrome test, redux
 

I recently read a description of rust bluing, which explains the patina revealed by Simichrome and Maglight as an inevitable (and ultimately undesirable) result of the process.

It made me wonder about salt bluing. Patina is rust, result of a rusting process. Since salt blue is not explicitly a rusting process, would it necessarily result in patina?

--Dwight

Dwight, Salt bluing is an oxidizing process. Rust or acid bluing produces ferric hydroxide which on exposure to air gradually becomes ferric oxide, the brown oxide we all recognize as rust. The ferric oxide is the converted by boiling water or steam to magnetic oxide also called ferro-ferric oxide. Salt bluing commonly uses a hot molten solution of sodium hydroxide and sodium nitrite. This basic solution at relatively high heat directly forms magnetic oxide. Without additves to the solution and proper after cleaning salt bluing may be even more prone to oxidation formation than rust bluing. Firearm blueing and browning by Bradford Angier is a good reference.

heinz