One of the greatest challenges facing crime scene examiners at the crime scene in developing fingermarks using conventional powders is selecting a powder that has the utmost contrast to the background it is being applied to; i.e. dark coloured powders for light coloured surfaces and vice-versa.

However, when an examiner encounters a multicoloured or densely patterned surface the choice of fingerprint powder can then become quite limited. To combat this difficulty, there have been a number of different luminescent fingerprint powders that have been developed which can develop fingerprints on these surfaces with the use of particular coloured light (wavelength) from an alternative light source (ALS) and an interference filter, usually in the form of a coloured goggle/lens of some kind.

To date, most of the luminescent powders on the market fluoresce somewhere within the visible part of the electromagnetic spectrum, that is 400–700 nm. One area of the spectrum that has been somewhat ignored, is the near infrared (IR) region, between 700– 1000 nm. Interestingly, plants tend to absorb visible light as ‘food’ through the process of photosynthesis, but they reflect back all IR light that cannot be absorbed. It is there that researchers from Foster + Freeman started their investigation of a suitable plant-based powder that would fluoresce in this near infrared range. What they discovered and developed was somewhat remarkable.

They came across a food additive called spirulina, highly popular in the food industry for its health benefits, especially in green smoothies. They processed the spirulina into a a size suitable for fingerprint development and called it fpNatural 1.

A preliminary study into the use of fpNatural 1 as a infrared fluorescent fingerprint treatment has recently been accepted for publication by the Forensic Science International Journal.

Results from the study showed that fpNatural 1 was great at developing latent fingermarks from polymer bank notes and wrapping paper due to their semi-porosity as well as the background interference/fluorescence from the inks printed into them. Moreover, the historical use of spirulina within the food industry has facilitated its long-term health effects to be well understood and it is proven to be safe; a pertinent factor when considering its deployment within the forensic arsenal.

IR

For further information see:

Seeing into the infrared: A novel IR fluorescent fingerprint powder. Roberto S.P. King, Peter M. Hallett & Doug Foster