vivitar+Kodak E100VS-13

I want to know how you got such high contrast with that brightness in the clouds and still get the fade to deep black in the sky. Is it in the film or are you doing this in post processing, i.e. dodging the print in the darkroom or using digital effects to edit? My guess is it's something about the film and how you're exposing it but I don't know. This is a stunning photo. I am amazed.