Soot fingerprints

Reveal fingerprints using soot!

Difficulty:
Danger:
Duration:
10 minutes
Soot fingerprints

Safety

  • Conduct the experiment on the plastic tray.
  • Keep flammable objects and hair away from flame.
  • Keep a bowl of water nearby while working with fire.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

What’s the best way to leave a fingerprint on the paper?

Make sure your hands are clean and dry. Place any finger in the center of the rectangle, keeping everything in-frame. Press down hard. Try not to touch the paper with your other fingers – this could hinder the experiment in the future. If the fingerprint isn’t clear, try rubbing your finger on your forehead to make your finger more oily, and then leaving a new fingerprint. This should help you make a clear print.

My tweezers melted slightly when I used them to hold the foil...

Don’t worry! Just continue the experiment.

Can I use ordinary foil for this experiment?

If you look closely, you’ll notice that the foil from the set is much thicker than ordinary foil. Unfortunately, this makes it difficult to replace with foil from another source. We strongly recommend using the foil we provide – it should suffice to repeat the experiment several times. Moreover, you can use a single piece of foil multiple times for this experiment.

Step-by-step instructions

Perform this experiment without gloves.

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For this experiment, you’ll need soot. You can use a candle as a source.

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Soot is a form of carbon, and is produced when paraffin doesn’t burn completely. Use a piece of foil to collect some soot.

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Reveal the fingerprint using the soot you’ve collected. Try collecting your relatives' and friends' prints too!

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Disposal

Dispose of solid waste together with household garbage.

Scientific description

Curiously, carbon is a single element that can comprise quite a few compounds. Take, for instance, graphite, diamond, fullerenes, even carbon nanoparticles – all of these are elementary substances made of only carbon atoms !

Graphite, while more compact than soot, has a layered structure that forms easily-separable “slices.” Graphite is thus able to leave traces on paper, making it useful in pencils. Another well-known carbon compound—diamond—has a well-packed, regular structure, which gives it outstanding strength and a characteristic brilliance. Cubic zirconia has similar optical properties—use your piece for reference!

That's interesting!

How else can we reveal fingerprints?

Do you want to be a detective for a day? You don’t necessarily need a lot of special equipment to find fingerprints! You can test any smooth, clean surface: glass, paintings, metal objects, linoleum, lacquered wood, paper, etc. You will need a powdery substance (soot, talc, crushed chalk, powder from a laser printer, crushed pencil lead) and a brush. Find a surface you’d like to test, apply the powdery substance with a brush, and gently brush away any excess. Cover any prints with adhesive tape if you’d like to preserve them. To keep them for your "records," stick the tape on a background that contrasts with the print itself.

The process of fingerprint identification is known as dactyloscopy. One of its most widespread and important areas of application is criminology. It is important to remember that even clean hands leave traces. Human skin contains what are known as sebaceous glands, which produce around 20 grams of oil all over the body every day. This thin layer of oil moisturizes the skin, makes it elastic, and protects us from germs. Most often, fingerprints are revealed by applying a colored powder to a surface – the same method that you used at home. Chemical methods of revealing fingerprints also exist, such as using iodine  vapor. Evidence is placed in a special container with iodine. The container is heated, the iodine evaporates, and its molecules diffuse into any oil  deposits (such as fingerprints) and tint them, rendering them visible to the naked eye or a camera lens. You can also treat a surface with a solution of silver nitrate (AgNO3), which reacts with the sodium chloride (NaCl) contained in sweat. This reaction forms silver chloride (AgCl), which darkens when exposed to light. Ninhydrin (C9H6O4) is another option – it reacts with the amino acids contained in the skin’s fatty secretions. Hidden fingerprints emerge a vivid purple.