Fingerprinting is an important element of crime scene investigation. You may have heard that superglue (cyanoacrylate) can be used to develop finger prints. But you might not be aware that this technique can easily be performed at home with everyday materials. So in this project, I am going to teach you how to develop fingerprints with the super glue fuming method.
Cyanoacrylate is the generic name for a family of strong, fast-acting adhesives that are generally labeled as “Super Glue.” In fingerprint fuming, the vapors of cyanoacrylate react with the chemicals that are found in fingerprints. This reaction leaves behind a white film that can be photographed, or copied onto tape strips. The resulting images can be further enhanced with powder of a contrasting color or photo editing software.
When using cyanoacrylate glue for fingerprint fuming, it is important to keep in mind that these glues have a short shelf life of about one year from manufacture if unopened, or about one month once opened.
Safety Notes:
1. The vapors of cyanoacrylate are toxic (http://en.wikipedia.org/wiki/Cyanoacrylate#Toxicity). Take the appropriate precautions to avoid accidental inhalation.
2. Super glue bonds to skin quickly and can easily stick your fingers together. If this happens you can soften the glue with a solvent such as acetone (nail polish remover).
3. Cyanoacrylate reacts strongly with cotton or wool and can burn skin.
A heating element is used to speed up the rate at which the pool of cyanoacrylate vaporizes and releases its fumes into the container. This lets you develop a print in as little as 10 minutes. Without the heater, the process might take over 24 hours to complete.
I recommend using a small 15-20 watt coffee warmer/candle warmer as the heater. Using a larger heater in a small closed space filled with combustible vapors can be a fire hazard.
You need a small container to hold the liquid super glue while it is being heated. You want to use something cheap and disposable because each fuming will leave behind a large patch of solid glue. The tray should be non-porous so that it doesn’t soak up the glue. It also needs to be able to withstand the heat of your chosen heating element.
There are a lot of regular household items that you could use. You could use a plain metal bottle cap or fold together a piece of aluminum foil into a small tray.
An important component of fingerprints is water. This water evaporates over time making it more difficult to develop a good print. So if the print is more than 24 hours old or if the air is very dry, then you need to put a small warm water reservoir in the fuming chamber. The warm water increases the moisture level in the chamber and on the print. This helps to develop the print faster.
Almost any closed container can be used to house the fuming process. However, here are some features that are good to have.
1. Air tight seal: Super glue fumes are toxic. So ideally, you want to keep them completely contained in the box. If this is not possible, you may want to tape the edges closed. And always be sure to set up your system in a well ventilated area.
2. Clear sides: You will want to check on your sample periodically. You don’t want to under develop or over develop your prints. It is much easier to check on the prints if your container has clear sides. That way you don’t have to keep opening and closing the container.
3. Just large enough for the sample, the heater and the water tray: If the container is much larger, it will take longer for the super glue fumes to spread and make contact with the sample. An appropriately sized container will help the prints develop faster and more clearly.
4. Convenient power cord access: You need a way to power your heater. So it is nice if there is a convenient way to feed the power cord into the container.
Now it is time to assemble the fuming chamber. Open the container. Set up the heater in one corner and put the glue tray on top of the heater. Place the water next to the heater. Set up the test sample in the corner opposite of the heater. You want to position it in such a way that the area with fingerprints will be readily exposed to the fumes in the chamber. The easiest way to expose both sides is to prop the sample up against the side of the container.
Once everything is in place, put a large drop (about half of a 0.07 oz tube) of super glue onto the glue tray. Turn on the heater and close up the container. Allow it to sit for at least 10 minutes. Then check on the development of the fingerprints. If the ridges of the fingerprints have developed into clearly visible white lines, then you are done and can remove the sample. Otherwise, put the sample back into the box and check on it again every 5 minutes until it is fully developed. You may need to add more super glue to the tray if the initial glue has dried up. Be careful not to let it develop too long or the spaces between each line will also turn white and make the print more difficult to read. I recommend doing several trial runs to get the hang of the process before attempting to develop any prints that you care about.
Now that you have developed the prints, you can make copies of them with fingerprint lifting tape. Alternatively, you can scan or photograph the fingerprints. Once you have an electronic copy of the prints you can further enhance them with your favorite photo editting program. The easiest way to do this is to use the Adjust Levels tool to change the brightness input levels. You can also enhance the prints by adjusting the Brightness and Contrast settings. Spend some time adjusting the settings until you find the best results.
