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Emily Sonnex

Identification of forged Bank of England £20 banknotes using IR spectroscopy

e.sonnex@pgr.reading.ac.uk

Infrared spectroscopy in ForensicsFT-IR has been used for many forensic applications

Infrared microscopy is a relatively new technique and currently has few forensic uses

Perkin Elmer Spectrum 100 with Spotlight 400 imaging system attachment (Beaconsfield, UK)

Figure 1. Perkin Elmer Spectrum 100 and Spotlight 400 FT-IR

Banknotes -Previous workVila et al. (2006), used ATR FT-IR to distinguish between

forged and genuine euro notes

Distinct differences in spectra between the notes

Little other work has been done in this field

Is it possible to do the same with notes from the Bank of England and develop a method for their identification?

Vila et al. Analytica Chemica Acta 559 (2006) 257-263

FT-IR of banknotes

ATR attachment on a spectrum 100

Additional peaks in the forged notes

Calcium carbonate

1400 cm-1 broad, stretching mode

879 and 715 cm-1 sharp, deformation mode

Figure 2. FT-IR spectra of genuine (top) and forged (bottom) notes, paper area

Simplifying the process

Nicolet IR 100 FT-IR by Fisher Scientific ‘spectrometer in a suitcase’

Identifying peak at 1400 cm-1 still present.

Figure 3. FT-IR spectra of genuine (top) and forged (bottom) notes, paper area

Investigating other areas of the note

The hologram section was also investigated

Several subtle differences observed

υ(OH) ~ 3500 cm-1

υ(C-H) ~ 2900 cm-1

υ(C=O) ~ 1740cm-1

Requires greater skill to identify differences in these peaks

Figure 4. FT-IR spectra of genuine (top) and forged (bottom) notes, hologram area

Taking it further

Spectrum 100 FT-IR with Spotlight 400 microscope attachment

Spectral imaging with principle component analysis

Mirrors the work of Villa et al.

Figure 5. Visible image and spectral map of a banknote with corresponding spectra, Forged (left) and Genuine (right)

Looking forward

The Bank of England has announced its intent to issue polymer banknotes from 2016

Australia is currently a large producer of polymer banknotes

Most of their detectable forged notes are printed on paper

Could the proposed method be extended to polymer notes even if the forgeries were printed on polymer?

FT-IR of polymer banknotes

The polymer notes can be distinguished from other readily available polymers

-Acetate

-PolyethyleneFigure 6. FT-IR spectra to compare genuine Australian banknote (top) Cellulose acetate (middle) Polyethylene (bottom)

Spectral mapping of polymer banknotes

Spectral maps of polymer banknotes were recorded

No spectral contrast seen other than black writing

May see a contrast if forged notes were produced on polymer

Figure 8. Visible image and spectral maps of an Australian banknote , Main body (left) and Black writing (right)

FT-IR of polymer banknotes

The polymer notes have two distinct sections – a clear window and the rest of the note

Both are distinctly different to forged paper notes Figure 9. FT-IR spectra to compare forged banknote (top) Australian

banknote printed section (middle) Australian banknote clear window (bottom)

With thanks to…