In message , Kevin
wrote
Dave Osborne wrote:
When I was a lad, if memory serves correctly, we used to dip hot
ferrous parts into a bucket of old engine oil. This gave them a
blue/black finish and I'm pretty sure we called it "blueing".
Anyway, I've been Googling and I'm a bit confused, cos blueing seems
to be a rust-proofing process which does not involve oil and
oil-quenching is a hardening process, not a rust-proofing process.
Can anyone put me straight? I was idly thinking about DIY oil
quenching to achieve moderate rust-resistance.
Do I need to use old engine oil, or will new be good/better/safer?
ISTR we heated the parts up to a dull red before quenching. Does
this sound right?
Cheers,
Rumble
from memory quencing in engine oil adds carbon and surface hardens the
steel, old oil has more carbon and therefore hardens more, I did this
as an apprentice years ago and i seem to remember they still rusted


From my often faulty memory from 40 odd years ago, wasn't blueing also
just an aid for 'marking out' the work. An easily removable dye gave a
blue surface colour on the 'shiny' metal on which you could scribe out
lines, by cutting through the dye so that you could easily see them..
--
Alan
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