Ink chromatography - a detective might use this if someone illegally changed the dollar amount written on a check or wrote a ransom note. You will need two different pens. Use two paper towels or coffee filter strips about 1-inch wide. Draw a dot on each paper with the pens. Make note of which pen you used for each paper. Place the paper in a cup of water with the dot just above the water line. As the water soaks up through the paper, you will see a distinctive pattern for each pen.