Jodie Louise Coulston

2016 AFPGR Participant


Nucleation and Growth of Silver in Physical Developer – From Ion to Fingerprint
About Jodie

Jodie is working towards completion of her doctoral degree in the Department of Chemistry, researching metal based fingerprint development techniques. Jodie is supervised by Prof. Rob Hillman and Vaughn Sears (CAST, Home Office).

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My Research

Fingerprints remain one of the most important types of forensic evidence due to their remarkable unique nature. Distinctive ridge patterns unique to each individual emphasise the use of fingerprint evidence as a powerful means of identification.

Fingerprints are associated with sweat and oils secreted directly from the fingertips and from touching areas of the body. This residue is transferred to surfaces upon touching, grabbing or holding an object. The residue itself is not visible to the naked eye, deemed a latent fingerprint, so must be visualised. The development technique is dependent on the type of surface: porous or non-porous. For non-porous surfaces the fingerprint residue resides on top of the surface but for porous surfaces, the residue will be absorbed.

My research explores the development of latent fingerprints from porous surfaces, notably paper, via Physical Developer (PD). Silver ions in solution are reduced to metallic silver particles which are deposited onto the fingerprint residue resulting in a grey/black mark. The efficacy of PD is widely accepted but the underlying fundamentals of the process are poorly understood. My research aims to fully understand the nucleation and growth of the silver ions in solution to silver particles on the surface.

Polymer banknotes are due to be circulated throughout the United Kingdom in autumn 2016, which means the familiar paper currency will be replaced. This poses the question as to how fingerprints will be developed on these semi-porous surfaces. Further understanding and optimisation of the PD process is imperative to the recovery of fingerprints on polymer banknotes.

Research Findings

My research to date has confirmed the spatial selectively observed with PD. Silver deposits onto the fingerprint residue and not the background paper surface resulting in high contrast. X-ray compositional analysis has shown that the grey/black silver deposits consist only of silver and not of other components of the developer solution.

Microscopic analysis reveals that the silver deposits are fairly monodispersed with a particle diameter range of 10 – 25 µm. There are areas of higher concentration of silver compared to others suggesting a preference to a component of the fingerprint residue. Studies to investigate the growth of the silver particles on the surface of the paper have indicated that the initial deposition of silver is fast (within 30 sec). A progressive growth is then observed within a 15 min development time.

Spectroscopic techniques combined with microscopy have shown that the silver particles in solution are an average of 876 nm in diameter. The silver particles on the surface of the paper grow ca. 10 x the size they are in solution, suggesting that the growth of silver occurs once silver has deposited.

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