Conversion temperature of red rust to black rust

[Ken Knight]

Somewhere read that the conversion temperature of red rust hematite Fe2O3 to black rust magnetite Fe2O4 on cast iron in an oven is 600 degrees, just wanted to confirm that temperature is correct. Do many here concern themselves with building up a magnetite layer on their CI before seasoning or am I overthinking that aspect of surface prep ? Thanks

 

[Doug D.]

It's hard without the benefit of hindsight to separate that which needs to be done, is better done than not, is not really all that necessary, or is just a lot of hokum. It is, however, a not-uncommon practice among collectors and restorers of cast iron cookware to raise the temperature of the clean bare iron above 500-550F because it has been observed to darken the iron. But this seems to be little more than an effort to accelerate the achievement of the black color associated with well-used CI, much like exceeding the smoke point of the seasoning oil can. I don't think turning red rust into black rust in this context is necessarily a required step.

 

[Ken Knight]

Thank you Doug.