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Revealing fingerprints

Award Level Bronze

 

Before you start your investigation you should carry out a risk assessment and have it checked by your teacher. For help with this, read through our health and safety information and look out for health and safety warnings in the text.

Fingerprints show up better on some surfaces than on others. A ‘latent’ print is one that is there, but not clearly visible. The aim of this project is to find out which methods are best for revealing latent fingerprints on different types of surface. You will also need to make a permanent record of the prints, to use as evidence in court for instance.

Getting started

Many factors may affect how well fingerprints show up. Here are a few you might like to investigate. You can probably think of some others. Lighting affects visibility so make sure your tests are done under similar levels of daylight or artificial light.

Type of surface

  • Test whether fingerprints show up better on smooth surfaces such as glass, crockery or gloss paint, or rougher surfaces such as paper or cloth.
  • Before you jump to conclusions, think about what might be causing the difference. Consider, for instance, why police take a suspect’s fingerprints on a sheet of paper, not on a sheet of glass.

Colour of surface

  • Check whether fingerprints show up better on light or dark surfaces.
  • Does the answer depend on whether the fingers are clean or dirty? For example, with mud, oil / grease or printing ink after reading a newspaper.
  • Are prints more difficult to see clearly on a patterned surface?

Revealing latent fingerprints

  • Forensic scientists ‘dust’ surfaces to make fingerprints show up better. Try various powders to see which reveal prints most effectively. Check whether the answer depends on the type and / or colour of the surface.
  • Iodine vapour can also be used to reveal latent fingerprints. You could try this, but be careful what you expose to iodine – it may permanently stain some surfaces.

Iodine is HARMFUL – avoid skin contact.

  • Fingerprints in blood may be left at a scene of violent crime, or just by a burglar cutting a hand on a broken window. You might think that bloody prints would be easily seen, but not necessarily. Find out how they can be ‘developed’ with chemicals to make them show up better. You could try it using animal blood, for example, from a piece of raw meat.

Some powders and chemical used to reveal fingerprints may be hazardous. Make sure you complete a risk assessment before you start your investigation.

Age of fingerprints

  • Fingerprints on a surface consist of liquids secreted by the body. Touching a surface leaves a pattern of liquid, corresponding to the ridges on the fingers – just like using a rubber stamp. So, what happens to the fingerprints as the liquid dries?
  • Investigate whether fresh fingerprints show up better than old ones? If so, how long do they take to fade? A few hours, days or weeks? Does it depend on whether the surface is porous.

‘Lifting’ and recording fingerprints

  • If revealing fingerprints involves using chemicals, you may need to remove the print from the surface first, to avoid the chemicals damaging the surface. This is called ‘lifting’. You could investigate various types of adhesive tape to see which picks up the best impression of the fingerprint from different types of surface. You may need to find a way to ‘develop’ the print on the sticky surface to make it more visible.
  • You also need to decide how to make a permanent record of the fingerprints. This needs to be portable, and as clear and detailed as possible, for use in court.

The results

When you have decided the best methods of collecting fingerprints check the effectiveness of your methods by holding a short ‘trial’. You will need:

  • A record of a fingerprint taken from a surface
  • An ink fingerprint taken from a ‘suspect’. The prints may or may not be from the same finger.  If different they should be of the same type (arch, loop or whorl), and similar enough that the answer is not obvious.
  • An independent judge (or jury).
  • A prosecutor, who has to convince the judge that the ‘lifted’ fingerprint is the same as the one from the ‘suspect’.
  • A defence council, who has to show that the prints are not the same.
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