Introduction to Fingerprints
1. What are fingerprints?
Everyone knows them, the grease fingers on a window. Those are fingerprints we say. We do not think further.
But a fingerprint is more than a fat print on a piece of glass.
Most prints are not useful for comparison, there is not enough information available in the print. Prints can be too old, too small, too dirty or damaged. Most fingerprints disappear after some days or some weeks. To know how to look at a print you need to know the basics of fingerprints.
The right definition of a fingerprint is strictly speaking the print (stamp) that a finger left on an object.
Besides fingerprints there are also other parts of the body that can leave good prints:
- The inside of the fingerprint,
- The inside of the hands,
- The bottom of feet and toe.
To understand where we are talking about we have to take a good look at the tips of our fingers. Use a magnifying glass to see it better!
Her you see lines in the skin that are higher than the surface. The lines are going in a certain direction. They look like a small dike with a dry ditch in between. These lines are called friction ridges. Sometimes there are small islands in between. The friction ridges are not always the same length, and are not always going in the same direction.
Sometimes a line stops or splits.
These are the unique points.
And that is the clue for the great mystery of the fingerprint!
Because there are so many lines on a fingertip and because they are stopping, starting or slitting so many times there are no two persons in the world that have the same fingerprints. Even a square millimeter is different at all persons!
Typica.
A fingerprint contains a lot of typica, unique lines. They are short or long, they can start, stop or split, they make figures, can be big, small or broad.
And above all it can happen at every place. So now you can imagine that no two fingerprints are the same. It is a little bit like a living-room, in all the world there will be no two the same living-rooms. Flowers, paintings, pictures, trash, furniture and music will make every living-room unique!
2. How does a finger leave a mark on an object?
First, because there has been a contact between the finger and the object. The fingers can leave there marks on different ways on the object. It can be done on several ways:
- The fat that is on the skin leaves a small layer on the object. That leaves a invisible stamp on the object. Sometimes you can see the stamp on a window.
- The friction ridges(ditches) on the fingertip makes marks in a soft underground. That happens in clay or putty.
- The fingertip makes contact with a dusty or dirty underground. Than a part of the dirt will be removed because of that a negative print will arise. It can be seen on a dusty window-frame.
- Acids in the fat of the fingertip etching in the surface of the object, For instance, on copper.
- A dirty finger can leave a mark, think of a finger with blood. The blood will leave a print.
3. Why are fingerprints important?
Searching with fingerprints has only one big reason.
To determinate to whom the print belongs.
An identification of a fingerprint is for 100% reliable. There is no other technique that can establish such a high standard. Even DNA does not give absolute certainty. A twin does have the same DNA structure but does have totally different fingerprints.
The fact that everyone in the world has different fingerprints can be used in very different ways.
Her are some examples for the use of fingerprints:
- Solving crimes,
- Identity control,
- Searching for identity with unknown dead,
- Entrance control at important buildings,
- Sometimes in a passport a fingerprint is included.
All around the world there are different standards to make an identification. In some countries it will be called an identification if there are somewhere between 7 to 15 identical points in the mark and fingertip. Other countries leave the identification over to the expert. It always is important that there are no unexplainable differences!
*Note: We’ll discuss this in class so you’ll really understand it.
We talk about explainable differences for instance when there is a scar on the skin, dirt in the background or on the finger, warts or differences because of the flexibility of the fingertip.
4. How do we search with a mark?
To compare a mark it is necessary to have the prints of a person.
To take the fingerprints of a person most of the time ink is used. Some ink is put on the fingertip and than the fingertip is pushed on a piece of paper.
This can be done under force (crime suspects) but it also can be done in free will.
The fingerprinting is mostly done at the police. They take prints of fingertips and of the palm of the hand. In some cases prints can be made from the foot.
Then all those prints go to a central computer. That computer is used to search with the found marks.
To take someone's prints of their ownfree will can be done by people that want to prove they are innocent or on identity papers. Sometimes prints are taken from unknown or dead people.
5. How can fingerprints made visible?
There are a lot of techniques that make it possible to make invisible prints visible. And to store them for further investigation.
The mostly used method is with powders. The powder will stick on the fat that has left there by the fingertip.
To store this mark it is possible to make a picture of it but it is much easier to do this with fingerprint tape. The tape is pushed over the mark and the print will be lifted on the tape. The print on the tape can be used for further investigation.
A method that is used very much is working with superglue. A little bit of superglue is being heated and it will vaporize. The vapor attaches to the fingerprint and that will become visible.
To find prints on paper you can use a fine iron powder. The iron will stick on the fingerprint.
To find older prints on paper ninhydrin (a chemical) is used. After a while it will color the prints purple!
There are a lot of other methods with all kinds of light or chemicals.
6. The way fingerprints makes figures.
The friction ridges are going parallel to each other and together they make a figure.
Global there are 3 main shapes:
- Friction ridges making an arch,
- Friction ridges making a whorl,
- Friction ridges making an loop.
From the shapes above a lot of other figures can be made but these are the most important.
7. The structure of a fingerprint.
Most fingerprints have a shape where there is a center visible. That center is called "the core", see top pearl. Another place is the place where a lot of lines come together "the delta", see bottom pearl.
In a fingerprint there can be a lot of lines. But there can be a great different in the amount of lines between one person or the other.
8. The future of the fingerprint.
Because fingerprints will always exist the always will be used. In the future there will be a lot of computers that can search with fingerprints.
And in the future there will be the need for a lot of people that can work with fingerprints. Because a computer can search for a matching print but it can never tell if it is a real identification. There is always the need for people that have to check the results of the computer.