Joseph Gwinn fired this volley in
:

Ferric chloride is not volatile (won't evaporate), is easier to
control and is safer, and for those reasons is a standard etchant for
steel.

Y'know, I've used ferric chloride to etch zinc, aluminum, and copper.
But I never thought to use it on any iron-based alloy.

I'm a bit confused about this. Is the ferric chloride actually etching
the iron, or just leaching other metals out of the alloy?

The reason I ask is, ferric chloride is chlorine and iron in its most
stable dimer state of Fe2Cl6. It can dissociate/reassociate
bidirectionally in aqueous solution to/from FeCl3, which is also stable.

So... my read is that it cannot actually etch iron. It can "stain" or
"reveal" features in iron by leaching out other metals, thus leaving a
distinct marking on the metal -- but not actually removing any
significant mass of the "etched" area.

When I think "etched", I think of fairly deep removal of the surface
metal -- i.e. "dissolved". My best bet is that your friend's blades felt
essentially the same across the "etched" areas as in all other areas of
the blade.

Yes? No?

LLoyd