Crimebuster: U of T forensic science grad tests unusual, 'slime'-based fingerprint technique

Could household slime become a tool to help solve crimes? That’s the question University of Toronto Mississauga graduate Leanne Byrne sought to answer in a recent study that tested a popular children’s "slime" recipe as a technique to enhance the appearance of hard-to-see fingerprints in forensic investigations.

Byrne, who studied forensic science and psychology, was intrigued by a technique developed by American forensic investigator Caleb Foster. But she wondered how the process might hold up under rigorous testing. Her curiosity led to an independent study co-authored by U of T forensic identification instructor Wade Knapp and lab technician Agata Gapinksa-Serwin.

The technique developed by Foster mixes a chemical reagent with a rubbery slime compound. 

“Reagent agents in the slime reacts with the fingerprint, producing a stain that enhances the detail so we can photograph it,” says Byrne, who revised and tested Foster’s technique, focusing on two reagent compounds often used by investigators: crystal violet and amido black.

“My method proposes an inexpensive technique that uses borax mixed with glue as the baseline compound,” she adds. The compound improves application process, cutting down on overspray and allowing for quick reapplication. “With this method, investigators can press the slime on the fingerprint, wait a couple of seconds and lift it up,” she says. “If it hasn't stained sufficiently, it can be reapplied as needed.”

The approach is in contrast to liquid chemical sprays or bath solutions that investigators typically use to enhance fingerprints for photography and analysis – a process that is often messy and results in waste of the reagent chemicals. 

U of T Mississauga grad Leanne Byrne tested slime mixed with reagent chemicals to determine if the concoction was effective at revealing hard-to-see fingerprints (photo courtesy Leanne Byrne)

Byrne tested the two reagent slime mixtures on different surfaces, including black electrical tape, beige and clear packing tapes, silver duct tape and painted wood tiles. She also varied the ages of the fingerprints and tested bloody and non-bloody prints.

The results of Byrne’s slime tests are encouraging. “The best enhancement was produced on black electrical tape and beige packing tapes,” she says. “It didn’t work as well with clear and duct tapes, so that shows the technique is better for some surfaces than others.”

Byrne found the technique enhanced hard-to-see details, as seen in this example of a bloody fingerprint before and after application of the amido black slime compound (photo courtesy Leanne Byrne)

Byrne says the study’s results warrant additional testing that combines other chemical reagents with different surfaces and variable fingerprint conditions.

“Fingerprints can change over time, depending on the environment and variables like temperature and humidity,” she says. “We can’t always tell the age of the fingerprint, so we want to make sure that a technique is going to work consistently regardless of the age.”

Byrne earned high distinction in the honours bachelor of science program. The self-confessed “true crime fan” and “huge lab nerd,” says that four summers of leading slime-making activities as a children's camp counsellor helped prime her for the unusual study.

The recent graduate, who plans to pursue a career as a forensic identification assistant with law enforcement agencies, says she is excited to contribute to new knowledge of analysis techniques. In May, Byrne presented her results in a virtual poster conference of the Canadian Society of Forensic Sciences. She also earned her first publication credit.

The slime study is forthcoming in the June 2020 issue of forensic journal Identification Canada.