Originally Posted by Trakhak

Hard treated, not heat treated.

FWIW, Jobst Brandt hated hard-anodized rims. The slick surface treatment, he said, reduced braking effectiveness. And the very thin, hard, brittle coating would form microcracks that would then propagate into the aluminum underneath, forming larger cracks, usually around the ferrules.

Interesting how some apparent innovations made a big splash and then disappeared rapidly. Seat stays with inserted carbon sections would be another example.

Edited to add link to Brandt's musings on the topic of hard-anodized rims.

https://www.sheldonbrown.com/brandt/anodized-rims.html