[Kyrie]

Originally Posted by DonVoigt

I believe your basic premise about "oxidized magnetite" is inaccurate.

The oxide formed from the temperature reached during straw coloring, is not the same as black oxide or rust blue.

I believe you will find that the straw color and the bright blue often seen are not related to cosmetic or "rust" treatment or prevention- but are the concurrent result of "drawing" heat treated and polished steel to achieve a particular hardness, flexibility, or to reduce internal stresses from prior heat treatment and forming.

In other words "straw" is not a primary objective, but a secondary effect of another action.
All the treatments you mention depend on proper care and application of oil , wax, or grease to prevent further oxidation.

That said, today the primary reason for "re" strawing is surely cosmetic. JMHO.

Well and truly said.