One of my all-time favorite images is Andreas Feininger's photo of Route 66. This photo was taken in the late 1940s and appeared on the cover of Life Magazine in 1953.

As seen here: https://www.life.com/photographer/andreas-feininger/

The contrast is incredible between the clouds and the black sky.

What techniques or equipment do you think he was using? What kind/size of film, camera?

I've tried to capture black skies with a red filter, but haven't ever come close to those skies!