Science Club: Forensics

As an avid fan of Forensic Files, I can assure you that I think forensic science is fascinating. As such, I figured it would be a fun idea to bring a little bit of it into science club. Specifically, we're concentrating on ink chromatography and fingerprints today.

Chromatography

Chromatography is the separation of a material (in this case, ink) into its component parts (in this case, the colors that make up the ink) by using a solution in which it dissolves (such as rubbing alcohol) on a medium in which different colors move at different rates (here, a coffee filter).

Basically: Different brands of pen will use different types of ink, which are all *slightly* different shades of blue. Perhaps one pen is a little more green, and another is a bit more purple, but it's hard to tell by looking right at the ink. What to do? Separate the ink into its component colors! Every pen will have a different pattern, and you'll be able to see which pen wrote the note.

The Story

I started by telling a very sad story: SOMEONE has stolen Miss Kat's chocolate! They left a note saying, "sorry!" but didn't sign it. How can we figure out whodunnit?

Well, I just so happen to have collected the favorite pen of three of my coworkers. I've already used chromatography to analyze the ink in the note - now we have to analyze the ink in the pens to see which pen wrote the note (and therefore which person ate my chocolate). 

You Will Need

• At least 3 pens of the same color, in different brands (I used blue pens, because it was easier to see the color differences in blue than black ink)
• Coffee filters
• Rubbing alcohol
• Clear plastic cups
• Pencils and small binder clips

Setting Up

Step 3: My guilty party.

1. Cut the coffee filters into rectangles, roughly 1" wide and 3" long. You will need 3 rectangles per participants, plus extras in case anyone messes up.

2. Label the pens, so we can keep track of which pen makes which mark. I labeled mine with the names of coworkers (with their consent), but using A, B, and C, or 1, 2, and 3 would work just fine. 

3. Use chromatography to separate out the ink of one of the pens, as described below. This is your guilty party, which the scientists will all try to match the suspects' pens to.

Chromatography

Each participant gets one lab report, three coffee filter rectangles, three binder clips, a pencil, and a plastic cup.

Take turns using the pens to write on the coffee filters; at the top of each, write the suspect's name. About 1/2" from the bottom of the filter, draw a thick horizontal line (or, scribble with pen enough that it looks like one solid line). 

Clip one binder clip to the top of each rectangle, and thread all three clips through the pencil. Add about 1/2" of rubbing alcohol to your plastic cup, and suspend your pencil and its test rectangles over the cup. The bottoms of the rectangles should reach the liquid, but the ink line should be above the liquid's surface.

Wait and watch in wonder as the ink starts to separate. It may take a good 15 minutes before your samples are done, so this is a good time to start on fingerprinting. (Of course, it starts right away, so sometimes it's hard to stop watching it...)

See that teal stripe at the bottom?
It was LAURA who stole my chocolate!

Once the ink has stopped separating, you can carefully remove the rectangles from the cup, and examine them to see which pen wrote the note - and therefore which coworker stole the chocolate.

NOTE: If you don't want to use rubbing alcohol, this experiment can be done with washable markers and water.

Fingerprinting

I had originally intended to use an ink pad for fingerprinting, but that can be messy, and there's an easier way.

What You Need

• Pencils
• 2 pieces of paper per participant
• Clear tape

What to Do

1. Using your pencil, make a large dark mark on your paper. 
2. When you have plenty of graphite on the paper, rub your finger in the spot until it's covered. 
3. Then, press the sticky side of a piece of clear tape to your finger and press down. 
4. Remove the tape and stick it to a piece of clean paper (or, in this case, the lab report). 
5. Repeat for all fingers.

Then, take a look at all the whorls, arches, and loops that your fingerprints have. Do any of yours match? Do they match anyone else at the table? They shouldn't! It's a one in a million chance that someone has even one fingerprint the same as you do. 

Lab Report

Here's the lab report I made up for Chromatography and Fingerprinting. I actually taped my Guilty sample to the "The Culprit" section of the paper and color-photocopied it before we began.