To detect and obtain the patterns of your fingerprint from any of your fingers.
Forensics, Crime investigation, etc.
This experiment contains toxic fumes, please be careful and check out our safety guide.
Fingerprint is the unique identity associated with different people. It is the pattern, or impression of the friction ridges, or the raised portion of the epidermis on the palm skin of all part of the finger. Such print may be deposited in natural hand secretions, or palmar sweat, and found on the palm sides of fingers. Identification of these fingerprints is an important system within police agencies, since lifting fingerprints from a crime scene can be used in forensic science to identify suspect or other people who touched a crime scene surface, or to recognize whether two fingerprints are from the same finger or palm.
Three types of prints, the plastic, visible finger print, and true latent prints are available at the crime scene. The plastics prints are ridge impressions on a soft material such as wax and the visible prints are ridge impressions on colored materials. Both types are directly visible to the eyes without any processing. Only the true latent prints, which is the transfer of body perspiration on finger ridge to the object surface, requires techniques to visualize the prints.
Prints on non-absorbent surface by skin or dermal ridges can be developed with powder, while the prints on soft or porous surfaces require the visualization using chemical processing techniques.
One of chemical technique used for fingerprint visualization is Iodine fuming. When finger ridges come in contact with a surface receptive to a print, materials on the ridges, such as oil, will be transferred to the surface. The patterns on the paper might be different depends on the pliability of the skin, the pressure applied by the finger, and the degree of smoothness on the paper.
Therefore, when finger is pressed against a white paper, different patterns of the fingerprints are let on the paper. 1 At this time, iodine can be heated to produce a violet vapor that is then absorbed by the fingerprint secretion to produce a yellowish brown pattern on the surface where the secretions are deposited. Such visualization is short lived and needs to be chemically fixed by mixing with starch.
- Solid iodine Crystal
- White Paper
- Benzene Burner
- Glass Tube
- Laboratory Clamps
- Laboratory Stands
- Power source
- Tweezer or Spoon
- Starch Solution
- Both Laboratory clamps and stands are recommended because they help to fix the position of the tube to be heated. However, if you have other methods for heating the solid iodine without your hand directly touching the tubes, these materials are not required. Similarly, Benzene burner and the tube is not required if you have alternative methods that is safer to heat the iodine crystal.
- Iodine fumes are toxic and corrosive. Therefore, special attention must be paid to prevent the direct contact between the face and the fume. Protection devices, such as goggle and gloves, which are normally used in different laboratories, are recommended. For the same reason, it is highly suggested to look directly into the tube to prevent inhaling any iodine fumes or vapors. Also, it is better to use tube with lid, in which the tube will be a closed chamber during heating, and it is still feasible to insert white paper into the tube after the evaporation of iodine. Please check our safety guide.
- The first step is to evaporate iodine throughout a tube with the lid on. A tube is washed and dried.
- A small iodine crystal is picked out of the container using sterilized spoon or tweezers. Weight the iodine.
- Attention: Make sure the amount of iodine is small, since the evaporation of larger solid might pushed the lid out of the tube.
- Attention: To ensure the tube will not be broken by dropping the crystal, the iodine solid is slipped along the side to the bottom of the tube while holding the tube in an angle.
- Clamped the tube onto the stand and fixed the position of the tube to make sure the tube bottom will be exposed to the exterior of the flame. Insert the lid into the tube. Place the benzene burner under the tube and lid it up using a match.
- Heat the tube bottom, where the iodine is located, for a short period of time until the purple iodine vapor spreads throughout the tube. Close the benzene burner. Right now black iodine deposition should present on the sides of the tube.
- Once the iodine sublimates throughout the tube, the secretions or unsaturated fatty acids in fingerprint residue will be transferred onto a porous surface, a.k.a, a white paper.
- Attention: Make sure no markings are presented on the paper and the fingerprints will be clearly recognized on the paper.
- Cut the big paper into slices to fit into the tube.
- Place the thumb fully onto the paper to get as much fingerprint as possible from your finger.
- Since the slightly different way for compressing fingers can result in different visualization of the fingerprint on paper, repeat the same process on at least three paper slides to ensure the quality of the result. Record down how hard you pressed your finger corresponding to each paper slide.
- After the secretions are obtained, insert the white paper into the tube and quickly close the lid.
- Attention: Opening the lid for a long time will let the iodine vapor flows out of the tube.
- Put the tube in front of a black background that more clearly shows the yellowish color of the fingerprint after absorbing the iodine vapor. At this time, the fingerprint should be clearly shown on the paper. Taken the paper out of the tube.
- Repeat the same process for all the paper slides containing fingerprints. Compare the results.
- Further step can be taken by dipping a glass rod into starch solution then spread starch solution using the rod onto the paper to permanently fix the fingerprint patterns onto the paper. Otherwise the iodine will evaporates onto the air and the fingerprint patterns will disappear from the paper.
Based on whether you press really hard onto the paper and the fingerprints fixed onto the paper, qualitatively, or determine the approximate force you need to apply to the paper in order to obtain a clear fingerprint of your thumb.
Does the fingerprint successfully appear onto the paper after placed into the tube and after fixed by the starch solution? Does more force required to obtain a clearer figureprints onto the paper? Were your fingerprints looking exactly the same when the fingerprints were obtained by compressing the paper using the same finger for multiple times?
Other parameters in the experiments can be examined as well. For example, tubes with different volume can be applied in different trials to see if the smaller volume of the tube can condense the iodine vapor inside the tube and give out clearer pattern of finger prints after the experiments. Similar, the different amount of iodine can also be tried in different trials, as well as the different location you placed the fingerprint inside the tube.
Not only does iodine can be applied in visualizing fingerprints, the similar protocol can be applied to cyanoacrylate fuming that forms white complex with the salt in figureprints. Similarly, silver nitrate, which reacts with the sodium chloride in the palmer sweat and forms complex, can be heated to fume and visualize fingerprint using similar protocol. Such complex needs to be visualize under UV-light, which is not accessible everywhere. Besides, silver is a heavy metal and much more expensive to purchase than iodine. Therefore, iodine is considered as a more accessible and realistic method to use.