One of my favourite 50's illustrators is the lesser known though very worthy James R. Bingham.
Bingham had many long, successful series illustration projects, especially with The Saturday Evening Post, and worked most often in a fully painted style. But every now and then he'd blow the doors off by doing a piece in one of his more experimental graphic styles. Here he uses an entirely un-painterly approach (you could almost say it has a paint-by-numbers-kit quality to it) to interpret water.
As startling as this piece is, I was even more astonished when I turned the page and discovered these two b/w with spot colour pieces, looking all the world like they'd been done by legendary comic artist and Sin City creator, Frank Miller - though from fifty years earlier!