Because experts routinely match crime scene latent prints to full rolled ten-print cards, we are collecting both forms for the repository. We also collected several palm prints in both latent and print card form.
What did we collect?
We collected latents from four different surfaces, including gloss-painted timber, smooth plastic, stainless steel, and glass. These were chosen in consultation with forensic professionals as the four surfaces most commonly encountered.
The glass surface also served as our nominated ‘perfect latent’ surface, which we use to collect the best-quality latent we can.
We collected latents from both the right and left hands, from three surfaces each. We collect right- handed latents from the smooth plastic, stainless steel, and glass. We collect left-handed latents from the gloss-painted timber, smooth plastic, and glass. Ideally, we would like to collect both right- and left-handed latents from every surface, but could not do so in the interest of time.
Using our freedom latent method, we also captured latent palm-prints. Palms aren’t typically used to interact with the majority of surfaces so we make the effort to include two surfaces that require a degree of palm interaction (gloss-painted timber and glass).
We collected two ten-print cards from participants so that we have an ideal recording of a person’s fingerprints that we could use to compare against latent fingerprints also from that person.
How did we collect it?
The latent prints were collected with three different powders. In conjunction with a glass surface, we use white powder to develop our ‘perfect latents’.
We also used magnetic black powder on our gloss-painted timber surfaces and our smooth plastic surfaces. We used plain black powder on the stainless steel surface.
To simulate real-world latents we asked participants to interact with our latent surfaces in a realistic and natural manner, akin to how they would interact with comparable surfaces in their daily life. We call this our ‘freedom latent method’. For example, we attached our gloss-painted timber surface onto a door face and ask participants to enter a room by pushing on the timber surface, thereby leaving representative latents. If forensic professionals typically encounter latents on a door face that are slightly smudged, then our latents should also reflect that smudging. We used plastic bottles for our smooth plastic surface, and so we asked participants to leave latents on the bottles by picking them up as if they were going to take a drink. We used a blunt chef knife as our stainless steel surface, and so we ask participants to safely pick the knife up by the blade. For the perfect latent, we would like to avoid realistic degradation to the quality of the latent, so we ask participants to, gently and evenly, place their hands onto the glass to leave latent prints. This way we aim to collect high-quality latents.
We used the following techniques to ensure that the latent print is of high quality:
- The participant cleans their hands and then touches their face and neck to ensure there are adequate oils on the hands.
- The perfect latent surface is a clean pane of glass, placed flat on the table in front of their participant
- Participants place both their hands onto the glass and attempt to press each point of contact onto the surface as evenly and cleanly as possible.
To record the 10 finger prints, we used a refillable ink pad to ink each digit, before rolling the digit onto the tenprint. Each ten-print card collects a fully-rolled impression of each single digit, followed by simultaneous plain (i.e. not rolled, but pressed) impressions of the right-handed fingers and the left-handed fingers, and finally a simultaneous plain impression of both thumbs. The recording of simultaneous impressions acted as a guard against accidentally recording a print in the wrong box on the card, e.g. recording the right index finger in the right middle finger box. We collected two of these cards per session.