Usually, when you stamp an image, you use ink. But a very attractive two tone effect can be achieved by substituting household bleach for your ink pad. Don't worry about your stamp, the bleach won't harm it in any way.
Saturate the paper towel with bleach (it should be wet, but not dripping). Then press your stamp into the wet paper towel. Stamp your image onto the paper just as you would if you were using ink. In a few seconds, the bleach will cause the stamped image to fade and create two tones of color on the paper. HINT- use the same stamp and a colored pad to create two tones of imprinted image and if you're feeling really adventurous, you can emboss a third version of the same image. If you do use another medium to stamp your image after using bleach, make sure that you clean the stamp off first.
To see a project using this technique Click Here