Also interesting
https://www.enginebuildermag.com/201...s-gasket-cant/ and
https://www.enginelabs.com/engine-te...ns-mls-copper/ and
https://www.enginelabs.com/engine-te...ns-mls-copper/
The first MLS head gaskets I saw were uncoated ones from the US I bought on USA based ebay motors an advertised as for a Buick V6's (and used for a Commodore V6 with ongoing head gasket oil sealing issues) and that MLS gasket actually came with instructions to spray them with a light coating of aluminium paint and that's where I started doing it with plain metal uncoated MLS head gaskets. I think if uncoated ones were still in the market I will still spray coat them this way.
It might also be that copper head gaskets were used earlier and even when used these days still usually require the application of spay coatings so when head gasket manufactures that had previously made copper head gaskets started making MLS gaskets some initially used and recommended similar coating processes.