We have seen this mirror coating on experimental planes before, by scaled composite.
Could it be to reflect directed energy?
That was the guess on those craft, as was testing new IRST technology as an alternative theory.
I guess vs microwave it might be more effective yet lasers able to damage aircraft are out of the visible light spectrum. If you fired an industrial laser at a mirror the backing paint would burn. In a modern mirror that’s aluminum in a vintage mirror it would be silver.
Don’t get me wrong I love the old school aluminum look on any aircraft (same for nose glazing on bombers or airliners) yet that’s the aesthetics. It’s the same side of me whom drools over classic American Cars. Those old land yachts like the Cadillac 62 series Sedan De Ville or who fauns over Art Deco and Victorian architecture.
I mean it could be anything they are testing however there is a reason why the bare aluminum look was only common in commercial aircraft post 1960s. It’s since fallen out there as the Aluminum surface sections are now either composite or aluminum alloy that is more corrosion resistant but doesn’t polish was well (another reason I say it’s not stripped of Ram but sporting some kind of replacement skin).
Pilots still use vision on occasion to look for targets. Highly polished surfaces reflect light making them easy to see at greater distances (see signal mirrors). Most military aircraft moved to subdued and matte finish livery even camouflage by the 1940s in war time. Sure there were some polished mustangs, B29, Me 109s but operationally they got painted real fast once fighting started. In the 50s it was back in silver but again o moved back to matte and camouflage. By the 1970s only VVIP military aircraft and some occasional special livery aircraft sport the bare metal.
Stealth Aircraft like F22 Generally are exceptionally hard to find on radar and IRST have short ranges unless you happen to get on the 6 o’clock of a stealth in burner. But the sky is massive. Making the fighter flashy seems like it would defeat the whole point. if you look at the current fifth Gen fighters in service they all sport standardized camouflage patterns meant to make it just that much harder to see at range.