A total of 101 kinds of 6 manufacturers' black pens were used in the experiment, including 42 kinds of ball-points, 58 kinds of marking pens, and 1 kind of brush pen. All characters were drawn on recycled papers used in copying machines. Characters were drawn with different pens on five sheets of papers with grid (sample 1). These characters were not obliterated. Visible, near-infrared, and middle infrared light photographs of sample 1 were taken and compared to select pens used in experiment 2. To demonstrate that there are obliterated writings that are undecipherable by the conventional near infrared light photography, but are decipherable by middle infrared photography, samples of obliterated writing were made (sample 2). Obliteration was done by covering the writings with a pen that contained nigrosine dye. The samples were prepared with different thicknesses of ink covering, which was controlled by the number of pen strokes used to cover the writings. Thinly obliterated writings (one to three strokes of ink covering) were deciphered both on near infrared light photographs and middle infrared light photographs; however, thick obliteration writings (four to seven strokes of obliteration) were deciphered only on middle infrared light photographs. 6 figures and 5 references