All of these were sketched in my Strathmore Windpower Sketchbook (9x12), and then scanned into the computer and colored with Adobe CS5 Photoshop, running in 32-bit-mode.
Fire uses created light sources in the upper left hand corner, and in the hair.
Earth used an image from NASA. I sketched the circle in as a guide, and then edited the earth into the place of the circle.
Water was finally created after 3-4 drafts.
All were colored in with low opacity, soft brushes (opacity around 7%-41% depending on situation).