Josh Rubin, Cool Hunting:

I vary between this info-dense watch face and the new ultra-minimal and very hypnotic Fire, Water, Liquid Metal and Vapor faces. And these faces are more special than Apple let on during their keynote. They’re not rendered—each face is high resolution video shot in a studio using real fire, water and vapor elements.

This is yet another example of the tremendous effort Apple puts into design detail. Check out the behind-the-scenes making-of video embedded below.