Thanks, glad you like them. A duotone is just a way of repersenting a grayscale image with two colors. All of these images use black as the first color then various other tones as the second. Once you convert an image to black and white in PS change the Mode from RGB to Grayscale, once in Grayscale mode the Duotone mode becomes available. The duotone dialog allows you to select the two tones you want and apply a custom curve to each to control what shades of gray are represented by which tone.