Developing Fingerprints - Ninhydrin
Developing Fingerprints - Ninhydrin
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Ninhydrin (Triketohydrinden Hydrate)
Ninhydrin reacts to amino acids, a substance you do sweat from your hands unlike fat which
is the reaction component of iodine. Another advantage to this
reaction component is that it will remain for a very long time on a surface, especially
paper. To give you an idea of how long it will last the way I would test a new mixture of
ninhydrin was to use it on a few of my cancelled checks that had not been handled for 3 to
6 months. If it developed prints then I new the mixture was good.
You can buy ninhydrin either pre-mixed in spray cans or squirt bottles or you can mix it yourself. If you want to mix it yourself you will need some ninhydrin crystals (triketohydrinden hydrate) which can be purchases through most police supply catalogs or you can purchase it from most chemical supply houses. You need to mix a 0.6 percent solution of ninhydrin with the carrier (either acetone or alcohol). Normally acetone is the most common carrier since it evaporates rapidly. A 0.6% solution means 20 grams of ninhydrin crystals to one gallon of solution.
For those people which are not familiar with acetone, this is a solvent that is not good to breathe and is extremely flammable. This is two of the cautions to be associated with the use or mixing of ninhydrin. Let me say that once more... Ninhydrin mixtures are an inhalation hazard and extremely flammable !!!. There I said it twice so when you burn down someone's house because you decided to light a smoke while spraying ninhydrin, don't try to come back on me (CYA).
To use ninhydrin on an object, which is usually paper and wood products or those things that will not react well with powders (i.e. porous materials), you simply spray the ninhydrin on the object and allow it to react. Reactions times vary with the surface, amount of amino acid and environment, but suffice to say that you should wait at least 24 hours for the reaction to fully take effect. Sometimes prints will continue to develop after the 24 hour period. So how much to you spray? Well be generous with the application of ninhydrin. You want to make sure that all the area that you want to print is covered well and that it is saturated well enough to insure a good coverage.
The prints developed will be purple-blue in color and they are, for the most part, permanent. Another Caution to be considered about ninhydrin is that it will cause most inks to run (this is because of the acetone base, acetone is the stuff used in most nail polish removers, super glue removers etc) so you should not use this process on things which may be examined for other reasons, such as handwriting analysis. If your not sure about what other examinations are going to be made on a document you need to check first before you spray that ransom note with ninhydrin.