Does Bluing leave a hard skin on metal?

[Shawnba67]

I faced off a blued action in the lathe and noticed that the first <.001 came off like powder. Really reminded me of cast iron. After that first skim cut the action machined beatifully. Its really got my curiosity going.
Another possibility is this action is rumored to be forged. I dont know if either of these things could cause " powdering"
And again the powdering was .0005 or so then cut normally.
Action was an Interarms mini mauser.

 

[Stan Taylor]

I faced off a blued action in the lathe and noticed that the first <.001 came off like powder. Really reminded me of cast iron. After that first skim cut the action machined beatifully. Its really got my curiosity going.
Another possibility is this action is rumored to be forged. I dont know if either of these things could cause " powdering"
And again the powdering was .0005 or so then cut normally.
Action was an Interarms mini mauser.

There will probably be people come on here an dispute my response but bluing hot bluing especially grows over time.

 

[Someoldguy]

Hot caustic bluing leaves a black oxide of iron. Rust.

 

[clowdis]

Bluing is rusting and that oxide is harder than the parent material.

 

[Eddie Harren]

"that oxide is harder than the parent material."

Yeah. It's so hard that a "Scotch-brite" pad will remove it very quickly!

 

[JRS]

Bluing is also easily polished off.

 

[MDSpencer]

If it was a Remington. That coating is most likely phosphate