Note: there are FOUR videos on this page, and FIVE experiments!

Every crime scene has a silent witness called physical evidence, and fingerprints are one kind of physical evidence. The patterns of ridges on both the finger and toe are unique to each person; no two are alike, which allows fingerprinting to help identify who did what, when, and where. Your fingerprint pattern will never change throughout your entire lifetime, which makes it a handy tool for identification. The main patterns are arch, loop, and whorl.

Fingerprints are friction ridges made up of a single row of pores in your skin. When your finger touches a surface, oil and sweat transfer from your finger to the surface and leave an impression of the ridge pattern from your finger.

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There are three types of fingerprints: plastic, patent, and latent. Plastic is when a fingerprint is intended and makes a three-dimensional impression, like pressing your finger onto soft wax. Patent fingerprints are visible – these are the ones your mom gets upset about when she sees your prints all over her mirror or windows. The most common type of fingerprint is the invisible mark (latent), which require either a chemical reaction to be made visible or physical treatment.

Materials:

• pen
• index card (or download this FBI fingerprint card)
• number 2 pencil and pencil sharpener
• 3/4″ transparent sticky tape
• magnifying glass
• ink pad
• photocopier
• small ball of clay (golf ball size)
• 4 microscope slides
• graphite powder with adult supervision
• goggles and gloves
• paint brush or old makeup brush
• disposable paper cup
• scissors
• clear silicone (hardware store) OR gummy bear candy (see variation step #11 in Experiment Part 3)
• 4″ square of aluminum foil
• 3 feet of string
• string
• duct tape
• empty clean glass jar with a lid (pickle, jam ,or mayo jars work great)
• black sheet of paper
• crazy glue or super glue
• black objects (glass, metal, or plastic)
• iodine crystals (adults only)

Experiment Part 1: Lifting Patent Fingerprints

1.  Sharpen your pencil.
2. Lay a piece of tape down sticky-side up by touching only the edge of the tape.
3. Rub your pencil on your fingertip using the side of the pencil.
4. Touching the finger to the sticky side of the tape.
5. Gently pull your finger from the tape and pace it on the card. Trim off any excess tape.
6. Repeat for all fingers (and toes if you wish).
7. Carefully examine the prints under a magnifying glass.  What type of fingerprint do you have? Look at the ridge pattern (loop, arch, or whorl). You can use a photocopier to enlarge the prints so they are easier to see.
8. Are the prints clearer and easier to read using an ink pad or a pencil?

Experiment Part 2: Lifting Latent Fingerprints

(This next part works well if you have two friends to help you out.)

1. Clean all microscope slides using a soft cloth.
2. Close your eyes and ask one of your friends to secretly (without telling you which friend) rub their finger against the side of the nose or across the forehead (to oil up the fingertip) and then press it gently to the center of the microscope slide. Place this slide on the table face up.
3. Now have both friends oil up their fingertips using their foreheads or side of their nose, and touch the center of a slide (one friend per slide).
4. Put on your goggles and gloves, and do NOT inhale the dust! Sprinkle a small amount of graphite powder into a disposable paper cup (just enough to cover the bottom of the cup).
5. Dip the brush into the cup and lightly dist the center area of a microscope slide and twirl the brush to make a thin coating of graphite on the surface of the slide. As the print shows through, remove the excess by lightly brushing it away in the direction of the ridge lines.
6. Use the tape to lift the print from the slide to your card. Remember to hold only the edge of the tape!
7. Use your magnifying lens to match the prints and be able to tell which friend touched the first slide.
8. Now let your friends handle different objects, like a water glass, newspaper, magazine picture, construction paper, and other materials. Make sure they know which finger is making the print so you can match it to their original print from the slide.  Practice lifting prints from different objects and transferring them to the index / fingerprint card.
9. What if you use cocoa powder instead of graphite?

There are a number of ways to make invisible prints visible, depending on what the material is made out of. For porous materials like paper, rubber, cardboard or wood, you can use iodine fuming or ninhydrin to chemically react with the fingerprint and make the print visible (more on that in Part 5 below). For non-porous materials like glass or tile, you can use graphite powder, talcum powder (when you need the print to show up white instead of black), or cyanoacrylate fuming (refer to Part 4). The difference in the two types of materials arises because the porous materials can absorb liquid whereas non-porous are sealed , solid and smooth.

You can not leave fingerprints if you create a barrier between the surface you’re touching and your fingertips. You can either wear gloves, or use hand cream like DEB Hand Barrier which makes a second skin over your hand.

Experiment Part 3: Making an Artificial Fingerprint

1. Make a good fingerprint in the clay. Make sure you see ridgelines.
2. Cut off the tip of the silicone using scissors.
3. Apply a layer of caulk over the fingerprint, extending 1/2″ margin on all sides around the fingerprint. Press the caulk down with the tip to make sure you don’t have any air bubbles.
4. Let dry 24 hours.
5. Lift the caulk from the print using a fingernail and a lot of patience. Try not to bend, stretch, or deform the caulk print as you separate it from the clay.
6. Use your magnifying glass to look at the ridges in the caulk print.
7. Find a clean microscope slide.
8. Rub your finger against your nose or forehead, and rub that finger onto the ridges of the caulk print (artificial finger) and press the caulk print ridge-side down onto the slide.
9. Using the procedures from above, apply graphite to make the print visible and then transfer the print using tape to your card.
10. Compare the print from the artificial print with the original fingerprint. What do you notice?

Experiment Part 4: Superglue Reaction with Latent Fingerprints

1. Make a foil tray by bending up the edges of the square of foil. Place this in the bottom of the jar.
2. Attach the string to a black colored object using duct tape. The other end of the string is attached to the inside lid of the jar so that the black object hovers an inch or two above the foil tray.
3. Wipe the black object clean of all fingerprints.
4. Make a single, clear fingerprint on one side of the black object (rub your finger against your nose or forehead first).
5. Using gloves on your hands, place 20 drops of superglue in the tray. Don’t get this on your fingers!
6. Carefully lower the black object into the jar. Make sure it hovers above the tray. Screw the lid on tight.
7. Let it sit for 3 hours to develop the print.
8. When ready, unscrew the lid and remove the object and place it fingerprint-side-down on a photocopier and make a copy of the exposed print.
9. Roll up the superglue foil tray and throw in the trash. Be careful to handle this with your gloves on!
10. What other objects can you use for this fuming process?

Superglue contains a chemical called cyanoacrylate, which has fumes that react with the moisture in the fingerprint to make it visible.

TEACHER DEMO ONLY Experiment Part 5: Developing Latent Fingerprints with Iodine Crystals

Do NOT let kids do this experiment on their own. This is for adult / teacher demo purposes only as it involves handling iodine.

Never handled or worked with iodine? Do this experiment first.

1. After rubbing your finger on your forehead or nose, make a single, clear fingerprint on an index card.
2. Using foil, make a small tray (same procedure as Part 4 above) and place in the bottom of a glass jar.
3. Putting on your gloves and goggles, add about 10 iodine crystals to the tray. DO NOT INHALE FUMES OR TOUCH IODINE WITH YOUR BARE HANDS!
4. Suspend the index card with the fingerprint from the inside lid of the jar using string (same procedure as Part 4 above).
5. Lower the card into the jar and screw on the lid. Let this develop for 3-5 minutes. Look for a yellow fingerprint.
6. Open the jar. (Do you have your gloves on?) Remove the paper sample. Reseal the jar.
7. Look carefully at the exposed print. (Look quickly as this may fade.) Take a photocopy of this exposed print.
8. Open the jar. Place iodine crystals back in the original container and dispose of the foil in the trash.

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You can see what’s behind you with these easy to make rear-view spy glasses! Each lens has a mirror so you can see not only in front of you but also behind you. It’s quick to make and uses simple materials.

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Materials:
1 pair cheap sunglasses
2 small mosaic mirrors (like from a craft store)
Hot glue gun with glue sticks

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This super-cool project lets kids have the fun of playing tag in the dark on a warm summer evening, without the “gun” aspect traditionally found in laser tag. Kids not only get to enjoy the sport, but also have the pride that they build the tag system themselves – something you simply can’t get from opening up a laser tag game box.

Burglar alarms not only protect your stuff, they put the intruder into a panic while they attempt to disarm the triggered noisemaker. Our burglar alarms are basically switches which utilize the circuitry from Basic Circuits and clever tricks in conductivity.

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Can you spot a fake $10 from the real thing? It’s getting harder these days, but you can still do it using a microscope.

US dollar bills are make of a mix of cotton and linen, which is why they don’t fall apart when you leave them in your pants pocket and they go through the water. They also have trace amounts of iron embedded in them, so they flex slightly toward a strong magnet. Can you find the owl on the dollar bill?

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Newer US five dollar bills have a watermark. If you hold it up to the light, you’ll see another image appear that wasn’t there before.

Older fives have the names of 26 states written along the top of the building on the backside of the bill.

Five dollar bills also have strange borders on the front of the bill:

Fives also have microtexting printed right next to the name “Lincoln”:

Newer US ten dollar bills have an interesting mark. Look with your microscope at the bottom left corner at the “10”. Do you see how the lines inside are actually words?

The tens also have a unique color and loop patterns in the bottom right corner.

There’s also microtexting just above the name “Hamilton” on the front of the bill.

US twenty dollar bills have many different things you can spot with a microscope: the first is on the back of the sill, you’ll find a lot of little 20’s as watermarks scattered around the bill:

Microtexting on the twenty looks like this:

But what if you don’t have a microscope? Did you know you can create a compound microscope using just two hand held magnifiers? It’s all in how you use them to bend the light. This video below covers the fundamental basics of how two double-convex lenses can be used to make objects appear larger when right up close.

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Did you know that when you talk inside a house, the windows vibrate very slightly from your voice? If you stand outside the house and aim a laser beam at the window, you can pick up the vibrations in the window and actually hear the conversation inside the house.

First, I’ll show you how to build your own space-age laser communicator, then you can work on your spy device. The first thing we’re going to do is take the music from your iPOD (or stereo, or MP3 player) and transmit it on a laser beam to a detector on the other side. The detector has a earphone attached, so someone else can listen to the music from your laser. Weird, huh?

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If you find a white powder at the scene of a crime, how can you tell if it’s flour or something more dangerous? A detective uses a chemical lab to determine what the substance is. One of the things that scientists look for is pH, which is a measure of how acidic or basic the powder is based on either a color change or how much a substance reacts with baking soda.

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Acids are sour tasting (like a lemon), bases are bitter (like unsweetened cocoa powder). Substances in the middle are more neutral, like water. Scientists use the pH (power of hydrogen, or potential hydrogen) scale to measure how acidic or basic something is. Hydrochloric acid registers at a 1, sodium hydroxide (drain cleaner) is a 14. Water is about a 7. pH levels tell you how acidic or alkaline (basic) something is, like dirt. If your soil is too acidic, your plants won’t attract enough hydrogen, and too alkaline attracts too many hydrogen ions. The right balance is usually somewhere in the middle (called ‘pH neutral’). Some plants change color depending on the level of acidity in the soil – hydrangeas turn pink in acidic soil and blue in alkaline soil.

There are many different kinds of acids: citric acid (in a lemon), tartaric acid (in white wine), malic acid (in apples), acetic acid (in vinegar), and phosphoric acid (in cola drinks). The battery acid in your car is a particularly nasty acid called sulfuric acid that will eat through your skin and bones. Hydrochloric acid is found in your stomach to help digest food, and nitric acid is used to make dyes in fabrics as well as fertilizer compounds.

In this lab, you have several mystery powders as well as several clear liquids to identify. Set up the liquids along the length of the table and the powders along the width so you can keep track of which ones give you a reaction and of which type.

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Cryptography is the writing and decoding of secret messages, called ciphers. Now for governments these secret ciphers are a matter of national security. They hire special cryptanalysts who work on these ciphers using cryptanalysis. The secret is, solving substitution ciphers can be pretty entertaining! Ciphers are published daily in newspapers everywhere. If you practice encoding and decoding ciphers, you too can become a really great cryptanalyst.

This is a super fun lab! First, we’re going to learn about what florescence is, then we’re going to shut off all the lights in the house and go for a black light treasure hunt.

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The reason stuff glows is that fluorescent objects absorb the UV light and then spit it back almost instantaneously. Some of that energy gets lost during that process, and that changes the wavelength of the light, which makes this light visible and causes the material to appear to ‘glow’.

Here are some things that glow: white paper (although paper made pre-1950 doesn’t, which is how investigators tell the difference between originals and fakes), club soda or tonic water (it’s the quinine that glows blue), body fluids (yes, blood, urine, and more are all fluorescent), Vitamins (Vitamin A, B, B-12 (crush and dissolve in vinegar first), thiamine, niacin, and riboflavin are strongly fluorescent), chlorophyll (grind spinach in a small amount of alcohol (vodka) and pour it through a coffee filter to get the extract (keep the solids in the filter, not the liquid)), antifreeze, laundry detergents, tooth whiteners, postage stamps, driver’s license, jellyfish, and certain rocks (fluorite, calcite, gypsum, ruby, talc, opal, agate, quartz, amber) and the Hope Diamond (which is blue in regular light, but glows red).

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This experiment is for advanced students. There are many different elements inside of a star. But they are so far away that we can’t get close enough to study them… or can we? By studying the special light signature (called “spectral lines”) astronomers can figure out not only which element, but also the approximate temperature and density of the element within the star, in addition to getting an idea of what the magnetic fields look like, which tells us about stellar wing and what the planets might be doing around the star, or if there might be another companion star.

Spectroscopy is a very complicated science, so let’s get started by actually doing it, and we’ll figure out what’s going on along the way.

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Materials:

• spectral analysis kit
• matches and alcohol burner or candle with adult help
• safety goggles and gloves

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This project is for advanced students. Make sure you’ve completed the Police Siren project first!

This is a really cool one. You’re actually going to build a miniature radio station. You can broadcast your voice or music to a regular FM radio. It just has a very short range (about 100 feet, or 30 meters).

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Every voice has a unique pattern to it just like fingerprints, and scientists can see this pattern as wavy lines and whorls. In this activity, you’ll be able to turn someone’s voice into a pattern of lines and view their voiceprint.

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Materials:

• empty soup can
• balloon
• small mirror
• tape
• scissors
• hot glue gun
• laser or flashlight

You can use this device to identify a recorded voice or a live voice. Detectives use voiceprints to compare and identify a suspect by having the suspect say common words such as a, and, I, is, it, on the, to, we and you and then they compare the recording to find a match.

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If you have access to a microscope, then this lab is fun and easy to do. If you’re in the market for a microscope, you can view our microscope recommendations here. If you’ve got a microscope but just haven’t used it for awhile (or never), then look over the experiments here first to get you started. Cloth fibers, wool, human hair, salt, and sugar all look really different under a microscope. It’s especially fun to mix up salt and sugar first, and then look at it under the scope to see if you can tell the difference.

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1. Pull fibers from a fabric. If it’s super-curly, use a bit of tape at either end, stretching it along the length of the slide. Keep the tape near the ends so it doesn’t come into your field of view when you look through the microscope
2. Lower the stage to the lowest setting and rotate the nose piece to the lowest magnification power.
3. Place the slide on the stage in your clips.
4. Focus the hair by looking through the eyepiece and slowly turning the coarse adjustment knob. When you’re close to focus, switch to the fine adjustment knob until it pops into sharp view.
5. When you’re done, lower the stage all the way and insert a new slide… and repeat.
6. Find at least six things to look at from six different fabrics. Try cotton, wool, synthetic, nylon, rayon, etc.

After viewing the fiber specimens, you can bring them close to a lit candle and adult help for a flame test. Different fibers burn differently: some will continue to glow, smoke, or burn after taken from the flame, some fibers burn more quickly than others. Some fibers curl, others melt, and some don’t even catch fire at all.

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If you look carefully at color images inside of books with a magnifying glass or a microscope, you’ll find there are only four colors that make up all the different colors you see. We’re going to learn how to separate the color that makes up different color markers, which work the same was as the colored printed images in books.

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Materials:

• markers
• blotting paper, paper towel, or coffee filters
• water bottle
• scissors

The different chemicals in the ink travel at different speeds along the surface of the paper when mixed with water. This is used to separate substances into its components.

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