Materials Science

Share this article:

Materials Science

  • Join our comunity:

Plastic Banknotes: New Fingerprint Technique Means Criminals Can’t Avoid Capture

By: , Posted on: September 15, 2016

bank-note

The UK has just introduced plastic banknotes, almost 30 years after they were used for the first time in Australia. The polymer notes are designed to last longer and be harder to forge. But the new notes, which will replace the old cotton paper ones entirely by 2020, come with a challenge for police detectives and forensic scientists.

The existing techniques for obtaining fingerprints from paper notes won’t necessarily work for the new plastic money. However, our team at the chemistry department of Loughborough University has developed a potential solution.

The use of fingerprints in forensic science may date back to the 19th century, but in the UK alone it still plays a key role in bringing charges in some 27,000 crimes a year, according to Home Office data we obtained. But new materials can pose significant challenges for fingerprinting. We’re forever trying to make things biodegradable, or handling devices that simply didn’t exist a decade or two ago.

The issue is that the new notes have been fashioned from “biaxially oriented” polypropylene, a type of plastic that has been strengthened by stretching it in two directions. They are also, as with all notes, deliberately fiddly in design. Illustrations and security features such as foil and transparent sections make it harder to develop a perfect print.

Washing machine proof. Joe Giddens/PA Wire/Press Association Images

The key is to try to find a method that will make the design of the note invisible and just highlight the print. Conventional techniques, such as exposing the fingerprint to cyanoacrylate (“superglue”) fumes that stick to the moisture in the ridges of the print and turn them white, can struggle in such circumstances. The developed print simply appears white and so is harder to see against the background, and it leaves an indelible mark or stain that means the note can’t be returned to circulation.

To overcome these various problems, we combined several techniques for revealing and capturing fingerprints that together can be used to successfully retrieve prints from plastic notes. This involves placing a thin layer of copper over the note that helps reveal the prints when illuminated with light of a certain wavelength, rendering the background of the note effectively invisible. You can also then cover the note in a forensic gel, which is usually used to retrieve footprints and similar marks at crime scenes. The gel is then peeled off and treated to reveal and preserve the prints.

The process relies on a technique known as vacuum metal deposition, VMD. This involves placing the sample in a high-vacuum chamber and then heating copper wire until it effectively boils. The resulting vapour is then allowed to condense in a layer of precisely defined thickness.

Revealing the prints. Shutterstock

Once the copper is in place, the note is illuminated with light of many different wavelengths. To the naked eye the results appear underwhelming. But if filters are used to just let near infra-red wavelengths through, then the prints are revealed against an almost invisible background.

We now need to test whether the technique can work on notes that have been through the washing machine or degraded over time. Predicting just how this would change surface interaction with prints is not so easy. But our method combines two technologies (VMD and imaging systems) that are already well established in forensic circles.

The added bonus is that an invisible layer of copper just a few nanometres thick wouldn’t damage the notes and they could easily be returned to circulation. So forensic scientists should be able to start gathering evidence from the new plastic notes right away, without having to put their impressive durability to the test.

This article is written by Paul Kelly, Reader, Loughborough University, UK. This article was originally published in The Conversation under a Creative Commons Attribution No Derivatives license. Read the original article here.


If you found this article interesting, these books are available in print and eBook format on the Elsevier Store at 30% off the list price and free global shipping. Apply discount code STC215 at checkout.

biaxial stretching of film

Biaxial Stretching of Film reviews the fundamental principles of biaxial stretching. After an introductory chapter which defines terms, chapters discuss equipment design and requirements, laboratory evaluations, biaxial film structures and typical industrial processes for the biaxial orientation of films. Additional topics include post production processing of biaxially stretched films, the stress-strain behaviour of poly(ethylene terephthalate) and academic investigations of biaxially stretched films.

multilayer flexible packaging

Multilayer Flexible Packaging provides a thorough introduction to the manufacturing and applications of flexible plastic films, covering materials, hardware and processes, and multilayer film designs and applications, giving engineers and technicians a better understanding of the capabilities and limitations of multilayer flexible films and how to use them to make effective packaging

handbook of polymers

Handbook of Polymers, provides the most sought after data for over 200 of the most widely used polymers, presenting normalized, up-to-date data in a consistent and easily referenceable layout that includes new values for many commercially available products and verification of existing data

Connect with us on social media and stay up to date on new articles

Materials Science

The highly interdisciplinary field of materials science examines elements of applied physics and chemistry, as well as chemical, mechanical, civil, and electrical engineering. Nanoscience and nanotechnology in particular have yielded major innovations in this area, such as graphene and carbon nanotubes. Elsevier’s authoritative content in this area ranges from undergraduate textbooks to multi-volume reference works investigating the relationships between the structure of materials and their properties. Our journals (including Materials Today), books, and eBooks help researchers stay abreast of developments in this swiftly advancing field, coving major sub-disciplines like energy and power; metals and alloys; ceramics; composite materials; polymer science and biomaterials; interdisciplinary materials science; and structural materials.

Social Media Auto Publish Powered By : XYZScripts.com