Drawn by hand in pencil on notebook paper (intended medium by the way), scanned in, and made into icons. Only touchups done were sharpening, erasing stray marks not part of the icon, resizing, etc.
Icons are in the following sizes (one .ico file includes all three sizes):
in the following bit depths:
32-bit (XP only)
Also included are 128x128 .PNG files for porting (see Creative Commons license) which should work as-is in most *nix GUIs.
If I'm missing an icon that this set needs, please let me know.