| Sažetak | U postupku analize krivotvorenih novčanica kao osnovne metode vještačenja danas se koriste
vizualne metode analize. Takva vizualna analiza u pojedinim slučajevima dovodi do
zaključka da krivotvoreni primjerci potječu iz istog 'izvora' što zapravo podrazumijeva da ih
je izradio isti krivotvoritelj ili povezana skupina krivotvoritelja. Međutim, postoje slučajevi u
kojima navedene vizualne metode nisu dostatne te je stoga u postupak analize krivotvorenih
novčanica nužno implementirati znanstveno potkrijepljene i dokazano primjenjive metode za
analizu papira i primijenjenih tehnika reprodukcije te njihovu usporedbu. Svrha ovog
istraživanja jest istražiti potencijal primjene mikro-Ramanove spektroskopije i energetsko
disperzivne fluorescencije rendgenskih zraka (engl. Energy Dispersive X-Ray Fluorescence;
EDXRF) kao nedestruktivnih metoda analize krivotvorenih novčanica izrađenih na papirnim
podlogama ispisom tonerom, inkjet tintom ili ofset-tiskom. Cilj istraživanja jest dokazati da su
mikro-Ramanova spektroskopija i EDXRF metoda uspješno primjenjive u analizi
krivotvorenih novčanica. Svrha ovog istraživanja jest unapređenje postupka vještačenja
krivotvorenih novčanica implementacijom znanstveno utemeljenih metoda analize. Sukladno
tome izabrani su uzorci koji odgovaraju najčešćim stvarnim uvjetima analize krivotvorenih
novčanica neovisno o valuti i imitiranoj nominalnoj vrijednosti. Snimanja svih uzoraka
provedena su na način da je obavljena izdvojena analiza elemenata reprodukcije u
plavozelenoj, purpurnoj, žutoj i crnoj boji. Zaključeno je da pojedini papiri posjeduju
karakteristične ramanske spektre čije vrpce se opažaju u ramanskim spektrima inkjet tinte,
tonera ili ofsetnog tiskarskog bojila, snimljenim direktno na tim papirima bez prethodne
pripreme. Ovom metodom moguće je zasebno analizirati ramanski spektar tonera, inkjet tinte
ili ofsetnog tiskarskog bojila te ih uspoređivati s ramanskim spektrima drugih tonera, inkjet
tinti i ofsetnih tiskarskih bojila koji su obrađeni na isti način, bez obzira na karakteristike
papira na kojima su ispisani. Pobudno zračenje od 784.3 nm učinkovitije je u svrhu
diskriminacije uzoraka kako ofsetnih tako i uredskih papira, od pobudnog zračenja od 514.5
nm. Pobudnim zračenjem od 514.5 nm moguća je međusobna diskriminacija tonera, inkjet
tinti i ofsetnih tiskarskih bojila. EDXRF metodom mjereni su kemijski elementi u uzorcima
različitih papira i procesnih boja te je moguća analiza i diskriminacija različitih vrsta papira.
Usporedba plavozelenih tonera, inkjet tinti i ofsetnih bojila kao i crnih inkjet tinti mogla bi biti
moguća jedino na osnovu analize količine bakra u pojedinim uzorcima. |
| Sažetak (engleski) | Usual methodology of counterfeit banknote analysis comprises optical methods of
examination under the visible, ultraviolet and infrared electromagnetic spectrum. These
methods serve to collect as much as possible information about the paper, toner, inkjet ink,
ofset ink, security features' imitations and identification of the reproduction techniques. The
same methods are used for the comparative analysis of the two or more samples of counterfeit
banknotes on which basis the conclusion about the similarities and differences between them
can be made. In some cases this kind of analysis leads to the conclusion that the source of the
counterfeit samples is the same what implies that they were made by the same or organized
group of counterfeiters. Most of the counterfeit banknotes, regardless of the currency, are
offset printed followed by less numerous inkjet (or similar water based inks) and toner printed
copies. Optical methods as the tool for determining the similarities or differences between two
or more specimens of counterfeit banknotes in a comparative expert analysis are sufficient in
most cases related to currency counterfeiting. Difficulties begin with counterfeit currency
cases where different nominal values or currencies without the distinctive imitation of
security features are made by the same perpetrator. There could be also the counterfeit
banknotes cases where the imitation of security feature is distinctive but is easily available for
use to different perpetrators and the printing technique and substrate of the counterfeited
banknotes are more or less different. In both circumstances the expert cannot rely on the
optical comparison of inks or paper only. The newest challenge for counterfeit banknote
experts in currency counterfeiting criminal offences could be the sharing or selling of prepress
data files electronically when the same reproduction of motives of original banknotes become
available to different perpetrators, printing counterfeit banknotes on their own initiative,
which probably implies the use of substrates and inks with different properties. In the
counterfeiting cases of the same denomination and currency and even the same serial number
when counterfeit banknotes appear identical at the first glance but detailed analysis of the
optical characteristics and reproduction techniques implies possibility that they are coming
from different sources, additional analytical techniques of paper and reproduction techniques
are also needed in order to determine commonality or dissimilarity of two or more counterfeit
samples. In all above mentioned hypothetical currency counterfeiting circumstances,
additional methods of analysis of ink and paper and their comparison are crucially needed,
besides already applied physical and optical analysis, in order to decide whether counterfeit
banknotes are coming from the same source or not. Therefore, in addition to the existing
optical methods of counterfeit banknote analysis it is necessary to implement scientifically
based and proven workable methods for the analysis of paper and applied reproduction
techniques and their comparison in the counterfeit banknote analysis methodology. In some
cases such methods would only give scientific confirmation of the optical analysis results, and
in the remaining cases would provide a proof of identity or difference between two or more
counterfeit banknote samples, individually analyzed in a scientific manner, regardless of their
visual similarity or dissimilarity. The result of such counterfeit banknote analysis
methodology would have greater impact and credibility when presenting the expert opinions
in judicial proceedings.
Raman spectroscopy and Energy Dispersive X-ray Fluorescence (EDXRF) are analytical
methods already applied, although not systematically, in the questioned document analysis.
The purpose of the research conducted in the framework of this doctoral thesis is to explore
the potential applications of micro-Raman spectroscopy and EDXRF as a non-destructive
methods of analysis of counterfeit banknotes produced on paper substrates by toner, inkjet ink
or offset printing. The research objective is to prove that the micro-Raman spectroscopy and
EDXRF are successfully applicable in the counterfeit banknotes analysis. Raman
spectroscopy was performed on the system Jobin Yvon T64000 with a monochromatic light
source of 514.5 nm wavelength in the micro-Raman mode and Raman system Maya 2000
with a monochromatic light source of 784.3 nm wavelength. EDXRF technique was
performed by Siemens's W X-ray tube and Canberra Si(Li) detector with a Mo secondary
target in orthogonal geometry. The purpose of this research is the improvement of a
counterfeit banknote analysis methodology through the implementation of science-based
methods of analysis. Accordingly, selected specimens correspond to the most common real
conditions of counterfeit banknotes analysis with regard to paper type and reproduction
techniques and regardless of the currency and denomination. Twelve toner specimens, ten
inkjet ink specimens and eighteen offset printing ink specimens are subjected to analysis.
Measurements for all specimens were analyzed in such a way that a reproduction elements of
each process colour, cyan, magenta, yellow and black, was analyzed separately. Keeping in
mind the initial idea and the purpose of this research and the possibility of the final
implementation of presented methods in the counterfeit banknote analysis, it should be noted
that the main objective of the application of either Raman spectroscopy or EDXRF in the
forensic analysis of counterfeited banknotes is to establish, confirm or refute the commonality
or dissimilarity of two or more specimens of toner, inkjet ink, offset printing ink or paper.
Therefore, the focus of interest of this research is not to determine the physical or chemical
characteristics of the specimens but their interrelationship without taking into account their
visual characteristics that could be studied by means of conventional methods of graphic
reproduction and graphic materials analysis.
When applying Raman spectroscopy with a monochromatic light source of 514.5 nm it was
necessary to choose only one dot of a specific colour in order to make a micro-Raman
measurement on approximately 1 square micrometer of the specimen. Comparisons of Raman
spectra were conducted on the basis of the presence of characteristic Raman bands in a way
that the Raman spectra are considered different if there is at least one difference in positions
of Raman bands between the two Raman spectra. It was concluded that some papers have
characteristic Raman spectrum that may affect the Raman spectrum of inkjet ink, toner or
offset printing ink, measured directly on that paper. Therefore it is important to consider it in
the application of Raman spectroscopy in the counterfeit banknotes or questioned documents
forensic analysis. In cases where the Raman spectrum of paper really affects the measured
Raman spectrum of a specimen, from the Raman spectrum of the specimen is necessary to
take away the Raman spectrum of paper most often with an aid of the Raman spectroscopy
system's software. Once the Raman spectrum of paper is cancelled by subtracting, it is
possible to make an independent analysis of the Raman spectra of toner, inkjet ink or offset
printing ink, and compare them with the Raman spectra of other toner, inkjet inks and offset
printing inks which are prepared in the same way, regardless of characteristics of the paper on
which they were printed on. Raman spectroscopy with a monochromatic light source of 784.3
nm is showed to be more effective in discrimination of paper specimens, than Raman
spectroscopy with a monochromatic light source of 514.5 nm. Discrimination of office and
offset paper specimens according to characteristic positions of the Raman bands is not related
to their affiliation to a particular manufacturer. Raman spectroscopy with a monochromatic
light source of 514.5 nm allows discrimination of yellow and magenta toners, while the
discrimination of cyan toners is not possible due to identical positions of Raman bands.
Measurement efficacy of cyan toner was 100%, yellow 83% and magenta 66%.
Discrimination of toner specimens according to characteristic positions of the Raman bands is
not related to their affiliation to a particular manufacturer. Raman spectroscopy with a
monochromatic light source of 514.5 nm provides discrimination of yellow and cyan inkjet
inks, while the measurement of magenta inkjet ink specimens was not successful.
Measurement efficacy of cyan inkjet ink was 70% and yellow 80%. Discrimination of inkjet
ink specimens according to characteristic positions of the Raman bands is not related to their
affiliation to a particular manufacturer. Raman spectroscopy with a monochromatic light
source of 514.5 nm did not provide discrimination of yellow and cyan offset inks, while the
measurement of magenta offset ink specimens was not successful. Measurement efficacy of
cyan offset ink was 94% and yellow 89%. The results of analysis of paper, toner, inkjet ink
and offset ink specimens by micro-Raman spectroscopy showed that the method allows
differentiation of different toners reproduced on different papers, different inkjet inks
reproduced on different papers and different offset inks printed on different papers. A
prerequisite of their discrimination is of course their different chemical composition.
Measurement of chemical elements in the specimens of different papers and process colours
reproduction elements was done by EDXRF technique. EDXRF analysis of 20 office and 20
offset papers on the basis of comparison of their Ca:Sr, Ca:Fe, Ca:Br and Ca:Ti ratios showed
that papers of different chemical composition can be distinguished by this method. Further
analysis of eighteen offset paper specimens and reproduction elements in cyan, magenta,
yellow and black showed that offset papers can be distinguished among each other. Measured
values were processed by BG-PCA statistical analysis. Analysis of the cyan, magenta, yellow
and black reproduction elements showed that only cyan toner, inkjet and offset inks as well as
black inkjet inks can be detected by this technique due to presence of copper (Cu) that can be
a base for their comparison. The latter was not proved by this research because information on
the chemical composition of the ink, toner or offset ink could not have been separated from
the information on the chemical composition of the paper with the applied EDXRF technique.
The findings that have arisen from the analysis of measurements done on the specimens in
this study are applicable in forensic analysis of counterfeit banknotes with the purpose of
identifying characteristic Raman spectra of paper, toner, inkjet ink or offset printing ink
specimens, as well as the chemical composition of the paper. |
