magnesium case plating?

On the magnesium transmission cases Porsche used through 1978, I remember some discussion in the past regarding an exterior plating they received, perhaps a chromate process of some kind. Does anyone happen to know / remember exactly what it was?

Also curious to know if there is anyone doing this type of plating at present in the US. I have a friend, actually a vintage Alfa Romeo racer / restorer / jack of all trades. He's got magnesium parts he'd like to see plated in a similar way, to help them survive the years.

TIA!

Perhaps this might be of interest.

https://ptiindustries.com/services/magnesium-coatings/

Mark

Here's a thread that might help as well:
http://www.early911sregistry.org/for...nesium-Coating

Cheers,
cm