Ink Identification

A ransom note is important evidence in a kidnapping investigation. If forensic investigators can identify the pen that wrote the note, they may be able to link the note to suspect. There are several ways to identify the type of pen used to write a ransom note or either criminal communication. Try the following activity to investigate one way to identify ink and the pen it came from.

Materials

- scissors
- coffee filters
- ruler
- water-soluble felt-tipped pens of different brands and different colors
- drinking glass
- tap water
- paper towel

Procedures

1. cut the coffee filters into several strips 1 inch (2.5 cm) wide.
2. Make a thick circle with one felt-tipped pen about 1 inch (2.5 cm) from the end of one strip.
3. Pour water into the drinking glass so that it fills ½ inch (1 cm) of the bottom of the glass.
4. Dip the end of the strip in the water so that the water covers about ½ inch (1 cm) of the end of the strip that you marked. The water should not touch the circle you drew.
5. Watch the water creep up the strip until it reaches the top of the strip.
6. Take the strip out of the water and place it on the paper towel. Above the filter, write the name of the color of the pen on the paper towel, using the same pen you used on the strip.
7. Repeat the experiment with the rest of the strips and pens.
8. Observe what happened to the circles made on the strips. What do you notice about the dyes in the pens?

More Fun Stuff to Do

Give a helper several different felt-tipped pens of the same color. Leave the room while your helper writes a short note, such as “Give me the money, or else!” on a coffee filter strip. Using the procedure you learned in the activity, can you tell which pen was used to write the note?

Explanation

Ink is complex chemical made up of several chemicals. Through a process called chromatography, complex chemicals like ink are separated into the chemicals of which they are made.

In this activity you performed an ink chromatography test. The colors of the inks separated in the different patterns because the ink colors are carried by the water at different speeds.

A forensic scientist can compare the chromatography pattern of the ink used to write a note with the chromatography patterns of several different known pens. This allows him or her to identify which pen was used to write the note.