Ninhydrin Prints
from Rubber Gloves

(This article is reprinted from the September 1966 issue of Fingerprint and Identification Magazine.)

by HOWARD A. SPEAKS, Senior Deputy
Los Angeles County Sheriff's Department

A burglar wearing gloves may create one of the most disappointing situations which can be encountered by the latent finger print officer. Until a short time ago, at least, the foregoing statement was true. Now it is possible, however, to obtain identifiable latent finger prints from the inside of rubber gloves.

The heavy type glove is clumsy to work with while plying a criminal trade. For that reason the criminal often selects a glove which will give him a more natural sense of touch. Rubber gloves have proven to be very satisfactory for that pose. A thin, flexible rubber glove makes it possible to separate sheets of paper with little effort.

Up to now, it was generally believed that no latent prints would be left when rubber gloves were worn, and that no latents could be developed on the soft pliable rubber used to manufacture such gloves. e relatively new method of development of latents with ninhydrin* has changed this outlook.  Rubber gloves, while aiding the burglar, also provide a very good surface for developing latent finger prints .

Hands Perspire Freely

The lack of air circulation and normal body heat cause the fingers to perspire freely in the gloves. The small amount of amino acid in the perspiration will react to the ninhydrin solution and produce a finger print pattern.

Recently,  in the Los Angeles area, a burglar was identified by finger prints even thou he was wearing rubber gloves during the entire period while he was at the crime scene. An extra office light burning at night was the down fall of the burglar. A cruising radio car crew noticed the light and decided to investigate.  The burglar, somehow alerted to the arrival of the officers, ripped off his rubber gloves and fled.  The alert officers saved the gloves for further investigation.

In the laboratory the gloves were carefully turned inside out to expose the portion of the gloves which had been in contact with the fingers.  The gloves were dipped in the ninhydrin solution and allowed to dry.  In a very short time friction ridges became apparent.

The procedure for making the finger print exhibit for court presentation was slightly different from that used under normal circumstances.  The glove finger was mounted on a piece of clear glass and placed directly in the enlarger.

The exposure time through the glove was slightly longer than normal, but the quality of the photograph thus obtained more than offset the inconvenience this method may have caused.  The positive finger print pattern on the glove, when used a negative, gave a reversal print.  Such reversed image will create no problem for the qualified finger print technician.  A positive print can be made easily when desired.

The tip portion of the latent on the glove revealed many ridge characteristics which do not appear in the routine inked impression.  This, of course, is caused by the fact that the glove follows the contour of the finger, while when taking inked impressions, only the flat underside of the finger is rolled.

In describing the use of ninhydrin in his previous article, Mr. Speaks recommended:

“The solution used in the ninhydrin process varies in strength from one investigative agency to another.  The percentage referred to in the early writings on ninhydrin is 0.4%, or four tenths of one percent.  The weaker solutions take much longer time to develop good latents, while stronger solutions take less time and do not seem to harm the latent.  A 1.5% of 1,2,3, triketohydrindene hydrate (the technical name for ninhydrin) in acetone or ethyl alcohol has at this time produced the best and fastest reaction time.

“The solution can be mixed on the basis of using 1.5 grams of triketohydrindene hydrate in 100 cc of ethyl alcohol or acetone.”  

(Editor --— This article was cited in a Technical Report  “Ninhydrin on Latex Gloves:  An Alternative use for an Old Technique,” published in the May/June issue of the Journal of Forensic Identification.  The cited author, Howard Speaks, was the first fingerprint instructor for many So. Cal. examiners--including myself, he has been a long time SCAFO member, author of several fingerprint articles and until late last year very active as a fingerprint consultant .  Thanks Howard for your many contributions to our science.)

This article was printed in “THE PRINT”
Volume 15(3) May / June 1999, pg 6
and has been obtained from the online library provided by the
Southern California Association of Fingerprint Officers
www.scafo.org