- Email: [email protected]
Discriminating red spray paints by optical microscopy, Fourier transform infrared spectroscopy and X-ray fluorescence
Forensic Science International 140 (2004) 61–70
Discriminating red spray paints by optical microscopy, Fourier transform infrared spectroscopy and X-ray fluorescence Filip Govaerta,*, Magali Bernardb a
NICC, National Institute of Forensic Science, Vilvoordsesteenweg 98/100, 1120 Brussels, Belgium b IPSC, University of Lausanne, BCH, 1015 Lausanne-Dorigny, Switzerland
Received 7 February 2003; received in revised form 26 September 2003; accepted 18 November 2003
Abstract Red spray paints from different European suppliers were characterised to determine the discriminating power of a sequence of analysing techniques. A total of 51 red spray paints were analysed with the help of three techniques: (1) optical microscopy, (2) Fourier transform infrared spectrometry and (3) X-ray fluorescence. Infrared spectra were classified according to binder type, filler and pigment composition and a searchable spectral library was created. Due to the difference in the elemental composition of spray paints, a further discrimination was possible. The microscopic analysis was not taken into consideration for classification purposes. The structure of the substrate under a paint coating strongly affects the surface characteristics of this spray paint. Together with the spectral library, a database of information of spray paints was build. # 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Spray paint; Chemical analysis; Discriminating power
1. Introduction Spraying paint is one of the fastest and easiest ways to apply paint. Spray paints are compact and commercially available everywhere. A spray paint is present in a closed container and no additional tools are necessary for use. Only one hand is needed to spray paint onto a surface or to put marks, signs or texts one wishes to be seen. Criminal offenders use these advantages to easily blot or destroy objects by spraying paint on them or by leaving signs at the place of crime with spray paints. Our investigations started in 1997, when the Animal Liberation Front (ALF) committed a series of attacks on restaurants, fur shops, mink nurseries and abattoirs in Belgium. In several cases the characters A, L and F were sprayed in black paint in the surroundings of the target. Till then few information was available concerning the chemical characteristics of spray paints [1,2]. For interpretation purposes, a collection of black spray paints was put together to build up a database * Corresponding author. Tel.: þ32-22400510; fax: þ32-22416105. E-mail address: [email protected] (F. Govaert).
of chemical characteristics of spray paints [3]. In this study, the same powerful analysing techniques [4] were used as Govaert et al. [3], i.e. (1) optical microscopy, (2) Fourier transform infrared spectrometry (FTIR) and (3) X-ray fluorescence (XRF) to investigate red spray paints. A new software-based spectral library was set up, using KnowItAll software package (Bio-Rad Laboratories, UK). This analysing sequence was evaluated on its discriminating power as well.
2. Materials and methods Forty red spray paints were bought in Belgian paint and do-it-yourself shops. The German Forensic Science Institute, Bundeskriminalamt, put 11 paint samples from red spray paints at our disposal. These samples were made according to the procedure described by Govaert et al. [3]. All spray paints origin from different European suppliers and they involve paints with different application areas and finishing types, i.e. mat, satin, brilliant, metallic, high temperature, car coatings, etc. All 51 red spray paints are listed in Table 1.
0379-0738/$ – see front matter # 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2003.11.015
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
Table 1 Collection of red spray paints Number
Brand
Colour
Supplier
Country
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
Altona Hammerite Trimetal Colorworks Levis Air Crafts Air Crafts Dupli-Color De Keyn Colorworks Gamma Motip Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Motip Leroy Merlin Motip Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dulpi Color
Signal red Red Brilliant red Signal red Red vermilion 62 Brilliant red RAL3020 Red tangerine 024 Fire red RAL3000 Fire red RAL3000 Brilliant orange red RAL2002 Signal red Brilliant fire red RAL 3000 Rosso (530) (Alfa Romeo) Hellrot (314) (BMW) Rouge vallelunga (GKB AC 44) (Citroe¨ n) Rouge furio (EJX) (Citroe¨ n) Rosso corsa (140) (Fiat) Flamencorot (2YP/R5) (Ford) Milano red (R81) (Honda) Rot (110) (Lada) Braze red (SQ) (Mazda) Monaco red (R82) (Mitsubishi) Red (526) (Nissan) Kardinalrot (508) (Opel) Magmarot (547) (Opel) Tizianrot (573) (Opel) Rouge vallelunga (1607) (Peugeot) Rouge andalou (EJZ/P3JZ) (Peugeot) Rouge flash (719) (Renault) Flame red (COF) (Rover) Rally red (911) (Seat) Super red (3E5) (Toyota) Super red III (3J6) (Toyota) Red mica met (3H4) (Toyota) Klassik rot (601) (Volvo) Marsrot (L31b) (VW/Audi) Tornadorot (LY3D) (VW/Audi) Rouge carmin brillant Rouge brillant Rouge feu brillant RAL 3000 Rot High gloss finish RAL 3000, flame red Flame red glossy RAL 3000, water based Red metallic effect Flame red glossy RAL 3000 Silk mat flame red RAL 3000 No. 5 red Red, elastic rubber Sun yellow-orange deco fluorescent Luminous red marking spray Flame red glossy RAL 3000
Herpe Hammerite Trimetal Nobel Motip BV Akzo Nobel Coatings AG European Aerosols European Aerosols Kurt Vogelsang De Keyn Paint Motip BV Intergamma Motip BV Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Motip Leroy Merlin Motip Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH
France UK Belgium NL NL NL NL Germany Belgium NL NL NL France France France France France France France France France France France France France France France France France France France France France France France France France NL Belgium NL Germany Germany Germany Germany Germany Germany Germany Germany Germany Germany Germany
2.1. Sampling Slight changes in sampling and measuring conditions were made compared to the former procedure [3]. Paint
was sprayed on microscopy glass slides (SuperFrost Color, Menzel-Gla¨ ser, Germany) from a distance of 0.3 m. The samples were allowed to dry horizontally for 72 h at room temperature. The adhesive tape, mounted on the glass slide
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
prior to spraying in order to transfer the paint samples easily to the XRF sample chamber, was not used anymore. For XRF analysis, paint samples from glass slides were directly collected by scraping with a scalpel and transferring the samples onto a large piece of adhesive tape. This made a simultaneous analysis of several paint samples possible. From each spray paint, three samples were prepared, for shaken as well as non-shaken cans, in order to make a reproducibility study.
63
the resolution was 20 eV per channel; the analysis-area diameter was about 2 mm and the measuring atmosphere was vacuum. Paint samples, with a diameter of 3 mm were transferred to a large piece of adhesive tape (Sellotape Diamond Ultra Clear, Holland) with a scalpel and tweezers. On this tape, around 60 paint samples were collected as depicted in Fig. 1. This piece of tape was mounted on the sample holder of the XRF spectrometer. With a programmable stage positioning, all paint samples were analysed in one sequence.
2.2. Microscopy 2.5. Spectral library and database A microscopic investigation of the coated glass slide was done, using an Olympus BX6O (Japan) microscope with up to 1000 magnification and bright- and dark-field observation. This microscope is equipped with a digital camera AxioCam HR (Carl Zeiss, Germany) to take images of paint surfaces using AxioVision 3.0 (Carl Zeiss) image acquisition software.
All measured IR-spectra were put inside a searchable spectral library using KnowItAll software package (Bio-Rad Laboratories). As properties of each spectrum, the brand, the colour name, the supplier and the country of purchase of the original spray can were given together with the elemental composition measured by XRF. It is possible to run queries using these properties.
2.3. Fourier transform infrared spectrometry (FTIR) An FTIR spectrometer (Nicolet 510P, USA) equipped with a KBr beam splitter, an IR-microscope (NIC-Plan, USA) and a mercury cadmium telluride (MCT) detector was used to analyse the chemical binders and fillers present in these coatings. One hundred scans were collected with a resolution of 4 cm1 and the intensity (% transmittance) versus wave number (cm1) was measured between 650 and 4000 cm1. Paint samples with a diameter smaller than 1 mm were transferred with a scalpel and tweezers to the window of a diamond compression cell (Micro Compression Diamond Cell, SpectraTech, UK). Once compressed, one diamond window with the sample attached was put on the sample stage of the IR microscope for analysis. The obtained spectra were interpreted and compared with our commercial and personal spectral libraries of paint materials. 2.4. X-ray fluorescence (XRF) To analyse the chemical elements present in spray paint coatings, XRF spectroscopy was carried out using a Kevex Omicron (USA) energy dispersive XRF spectrometer. The operating conditions were as follows: the accelerating voltage was 45 kV; the beam current was 0.1 mA; the collection time (life) was 100 s; the energy range/gain was 0–40 keV;
3. Results 3.1. Microscopy In this study, the microscopic analysis was emphasised on the morphologic characteristics of a paint layer. A colour analysis, a (micro-)spectrophotometric measurement, was not made. This kind of measurement requires a perfect homogeneous sample with uniform surface characteristics. These two requirements are often not present in real case spray paint samples. The influence of external circumstances on the surface characteristics is too high. Paint support can be rough or absorb paint leading to the absence of a uniform paint layer. Furthermore, coatings from non-shaken cans tend to be more brittle and get loose of the substrate than those emanating from rigorously shaken cans. All these variations hamper a comparative colorimetric study. In this microscopic analysis, the following types of paint were distinguished: mat, satin, brilliant and metallic. A metallic paint presents more characteristic elements, such as shape and distribution of the metallic particles, than the other three types that are distinguished by their difference in roughness of the surface (mat > satin > brilliant). An example of this difference in surface characteristics is illustrated
Fig. 1. Adhesive tape with 60 red spray paint samples for XRF-analysis.
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
Fig. 2. Different types of a red spray paint (Dupli Color, flame red RAL 3000) at 100 magnification and bright field observation (scale bar: 100 mm).
Table 2 Groups formed by infrared analysis with list of binder, filler and pigment composition and presence in this paint collection Group
Binder/filler/pigment composition
Presence as number of spray paints
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Alkyd–styrene Alkyd–magnesium silicate Alkyd-monoazo (CI Pigment Red 112) Alkyd–monoazo (CI Pigment Yellow 74) Alkyd–nitrocellulose Acrylic–alkyd Acrylic Acrylic–urethane–styrene-monoazo (CI Pigment Red 254) Acrylic–isophtalic–alkyd Acrylic–quinacridone (CI Pigment Red 122) Acrylic–perylene (CI Pigment Red 178) Acrylic–styrene Acrylic–magnesium silicate Mica–poly(dimethylsiloxane)-perylene (CI Pigment Red 178) Polyvinylacetate Styrene–epoxy–magnesium silicate Orthophtalic alkyd–calcite
1 1 8 4 23 2 1 1 1 1 1 2 1 1 1 1 1
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
in Fig. 2. The results of this investigation were not taken into consideration for discrimination purposes. Our investigation shows that only a uniform surface is obtained by reproducible spray conditions. This is of major importance to compare questioned samples. 3.2. FTIR When comparing three spectra from spray paint coming from the same spray can made under the same conditions
65
(shaken or non-shaken), only very little spectral differences were observed. The existing differences, fluctuation of the baseline, can be explained by the experimental conditions, i.e. the geometry of the paint particle on the diamond window. Internal reflections between sample and diamond window cause changes of the beam intensity at different wavelengths, changing the baseline position. The intravariability of these spectra is very low. Major differences exist between spectra of spray paints coming from shaken and non-shaken cans of the same paint.
Fig. 3. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 1–5).
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
These differences are observed in the fingerprint region of the spectrum. Some absorption peaks of ‘‘shaken’’ paint samples are not present in ‘‘non-shaken’’ paint samples. These peaks present in ‘‘shaken’’ paint samples only are of weak intensity. Indeed, in a non-shaken spray can, certain paint components settle down more preferably than others. When spraying, paint from the bottom of the spray can is pushed out at first. Paint samples under ‘‘non-shaken’’ condition, contain less material from the top of the spray can. In an IR spectrum, the specific absorbencies of these top
components are of a too low intensity to be observed or are overlapped by very intense absorbencies of components present in high quantities. A paint sample coming from a shaken can contains a higher quantity of the top components, due to a perfect homogenisation. This is observed in this infrared analysis: a spectrum from a shaken paint sample always contains the same peaks or more peaks than a spectrum from a non-shaken paint sample. For further analysis, the best spectrum (little noise, small baseline fluctuations) from each shaken paint sample was
Fig. 4. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 6–10).
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
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Fig. 5. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 11–15).
selected. These 51 selected spectra were compared one to another. This comparison permitted to form 17 groups according to binder type, filler and pigment composition. Table 2 lists the results of this comparison together with the typical binders, fillers or pigment components and the presence in this spray paint collection. Figs. 3–6 show infrared spectra of these 17 groups and illustrate that the typical characteristics can be clearly observed.
On basis of this distribution, the discriminating power (DP) of infrared analysis of spray paints was calculated according to Smalldon and Moffat [5], where: Number of discriminating pairs DP ¼ (1) Number of possible pairs or; DP ¼ 1
2M NðN 1Þ
(2)
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
Fig. 6. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 16 and 17).
with M the number of matching pairs and N the total number of analysed spray paints in the collection. Infrared analysis of this paint collection has a discriminating power of: M ¼ 289 and N ¼ 51
(3)
DP ¼ 0:773:
(4)
3.3. XRF The results of the X-ray fluorescence analysis of spray paints show more variations depending on the homogeneity of the paint inside the spray can when spraying. Indeed,
some quantitative and qualitative differences of chemical elements were observed between coatings emanating from shaken and non-shaken spray cans. As Zeichner et al. [1] described, coatings from non-shaken cans tend to contain higher concentrations of detectable chemical elements than coatings from shaken cans. This tendency was observed in this study as well. A qualitative analysis shows differences between shaken and non-shaken cans. Fig. 7 illustrates the comparison of shaken and non-shaken spray cans. A difference at one-element level is more frequent than no difference. The number of sprays that present a difference at two-, three- or four-element level decreases very fast. In each of
Fig. 7. Comparison of the elemental composition of a spray paint between shaken and non-shaken paint samples.
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
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Fig. 8. Presence (%) of chemical elements in paint collection.
these categories (one, two and three elements), the distribution of different elements was observed. When one or two elements are different, there are generally more elements detected in non-shaken samples than in shaken samples. In the category where three or four elements are different, there are not enough sprays to draw the conclusions. For discriminating purposes, the groups formed by infrared analysis were taken and those spray paints that are not discriminated with this method were compared according to the elemental composition, measured by XRF. A further discrimination is possible when the elemental composition of the sprayed paint is analysed. All measured chemical elements and their presence (%) in the spray paint collection are depicted in Fig. 8. FTIR followed by X-ray analysis permits to form 37 groups in total, with a maximum of four sprays in one group. The discriminating power of this sequence, FTIR followed by XRF, for the analysis of red spray paints was calculated according to Eq. (2) with: M ¼ 15 and N ¼ 51
(5)
PD ¼ 0:988:
(6)
4. Discussion The analysis sequence, infrared analysis followed by Xray fluorescence, proved to be successful to discriminate red spray paints. With a discriminating power of 0.988 a satisfying result was obtained. Only the instrumental analysing techniques were considered for differentiation purposes. Red spray paints present more different compositions than black paints [3]. Infrared analysis permits to classify
these paints into 17 different groups (only 6 out of 40 for black paints). Almost half of the red spray paints are composed of alkyd-nitrocellulose-based binders. To distinguish between spray paints with this type of binder system, a further analysis technique is absolutely necessary. This is obtained with the help of X-ray fluorescence. Twenty-one different chemical elements were analysed by X-ray fluorescence. The most frequent elements in this red spray paint collection are Ti (94%), Fe (84%), Ca (80%) and to a lesser extent Cl (64%), Zn (52%) and Si (46%). After X-ray fluorescence analysis, a group with a maximum of four non-differentiating paints was obtained. These four paints origin from the same supplier, but represent different colours. The same conclusion can be made for groups with three paints. Only in one group of two non-differentiating paints, two different brands were encountered. In this case (Leroy Merlin) the original manufacturer is unknown, but also here, the two colours are different. An additional colour analysis, i.e. spectrophotometry, could be very useful to discriminate these paints provided that a uniform surface is present. The searchable spectral library contains now the infrared spectra and the additional information of black and red spray paints, analysed at the Belgian Forensic Institute. Cooperating European colleagues are putting samples at our disposal for further analysis and consequently to fill up the database. A CD-ROM of this database will be distributed to interested forensic institutes. Acknowledgements This work was carried out during a work placement supported by the IPSC, University of Lausanne, Switzerland.
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The authors are grateful to the German Forensic Science Institute, Bundeskriminalamt, for delivering paint samples from spray paints. References [1] A. Zeichner, N. Levin, E. Landau, A study of paint coat characteristics produced by spray paints from shaken and nonshaken spray cans, J. Forens. Sci. 37 (1992) 542–555.
[2] C.D.J. Krausher, Characteristics of aerosol paint transfer and dispersal, Can. Soc. Forens. Sci. 27 (1994) 125–142. [3] F. Govaert, G. De Roy, B. Decruyenaere, D. Ziernicki, Analysis of black spray paints by Fourier transform infrared spectrometry, Probl. Forens. Sci. 47 (2001) 333–339. [4] B. Caddy, Forensic Examination of Glass and Paint, Analysis and Interpretation, Taylor and Francis, London, 2001. [5] K.W. Smalldon, A.C. Moffat, The calculation of discriminating power for a series of correlated attributes, J. Forens. Sci. Soc. 13 (1973) 291–295.
Discriminating red spray paints by optical microscopy, Fourier transform infrared spectroscopy and X-ray fluorescence Filip Govaerta,*, Magali Bernardb a
NICC, National Institute of Forensic Science, Vilvoordsesteenweg 98/100, 1120 Brussels, Belgium b IPSC, University of Lausanne, BCH, 1015 Lausanne-Dorigny, Switzerland
Received 7 February 2003; received in revised form 26 September 2003; accepted 18 November 2003
Abstract Red spray paints from different European suppliers were characterised to determine the discriminating power of a sequence of analysing techniques. A total of 51 red spray paints were analysed with the help of three techniques: (1) optical microscopy, (2) Fourier transform infrared spectrometry and (3) X-ray fluorescence. Infrared spectra were classified according to binder type, filler and pigment composition and a searchable spectral library was created. Due to the difference in the elemental composition of spray paints, a further discrimination was possible. The microscopic analysis was not taken into consideration for classification purposes. The structure of the substrate under a paint coating strongly affects the surface characteristics of this spray paint. Together with the spectral library, a database of information of spray paints was build. # 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Spray paint; Chemical analysis; Discriminating power
1. Introduction Spraying paint is one of the fastest and easiest ways to apply paint. Spray paints are compact and commercially available everywhere. A spray paint is present in a closed container and no additional tools are necessary for use. Only one hand is needed to spray paint onto a surface or to put marks, signs or texts one wishes to be seen. Criminal offenders use these advantages to easily blot or destroy objects by spraying paint on them or by leaving signs at the place of crime with spray paints. Our investigations started in 1997, when the Animal Liberation Front (ALF) committed a series of attacks on restaurants, fur shops, mink nurseries and abattoirs in Belgium. In several cases the characters A, L and F were sprayed in black paint in the surroundings of the target. Till then few information was available concerning the chemical characteristics of spray paints [1,2]. For interpretation purposes, a collection of black spray paints was put together to build up a database * Corresponding author. Tel.: þ32-22400510; fax: þ32-22416105. E-mail address: [email protected] (F. Govaert).
of chemical characteristics of spray paints [3]. In this study, the same powerful analysing techniques [4] were used as Govaert et al. [3], i.e. (1) optical microscopy, (2) Fourier transform infrared spectrometry (FTIR) and (3) X-ray fluorescence (XRF) to investigate red spray paints. A new software-based spectral library was set up, using KnowItAll software package (Bio-Rad Laboratories, UK). This analysing sequence was evaluated on its discriminating power as well.
2. Materials and methods Forty red spray paints were bought in Belgian paint and do-it-yourself shops. The German Forensic Science Institute, Bundeskriminalamt, put 11 paint samples from red spray paints at our disposal. These samples were made according to the procedure described by Govaert et al. [3]. All spray paints origin from different European suppliers and they involve paints with different application areas and finishing types, i.e. mat, satin, brilliant, metallic, high temperature, car coatings, etc. All 51 red spray paints are listed in Table 1.
0379-0738/$ – see front matter # 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2003.11.015
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
Table 1 Collection of red spray paints Number
Brand
Colour
Supplier
Country
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
Altona Hammerite Trimetal Colorworks Levis Air Crafts Air Crafts Dupli-Color De Keyn Colorworks Gamma Motip Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Motip Leroy Merlin Motip Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dupli Color Dulpi Color
Signal red Red Brilliant red Signal red Red vermilion 62 Brilliant red RAL3020 Red tangerine 024 Fire red RAL3000 Fire red RAL3000 Brilliant orange red RAL2002 Signal red Brilliant fire red RAL 3000 Rosso (530) (Alfa Romeo) Hellrot (314) (BMW) Rouge vallelunga (GKB AC 44) (Citroe¨ n) Rouge furio (EJX) (Citroe¨ n) Rosso corsa (140) (Fiat) Flamencorot (2YP/R5) (Ford) Milano red (R81) (Honda) Rot (110) (Lada) Braze red (SQ) (Mazda) Monaco red (R82) (Mitsubishi) Red (526) (Nissan) Kardinalrot (508) (Opel) Magmarot (547) (Opel) Tizianrot (573) (Opel) Rouge vallelunga (1607) (Peugeot) Rouge andalou (EJZ/P3JZ) (Peugeot) Rouge flash (719) (Renault) Flame red (COF) (Rover) Rally red (911) (Seat) Super red (3E5) (Toyota) Super red III (3J6) (Toyota) Red mica met (3H4) (Toyota) Klassik rot (601) (Volvo) Marsrot (L31b) (VW/Audi) Tornadorot (LY3D) (VW/Audi) Rouge carmin brillant Rouge brillant Rouge feu brillant RAL 3000 Rot High gloss finish RAL 3000, flame red Flame red glossy RAL 3000, water based Red metallic effect Flame red glossy RAL 3000 Silk mat flame red RAL 3000 No. 5 red Red, elastic rubber Sun yellow-orange deco fluorescent Luminous red marking spray Flame red glossy RAL 3000
Herpe Hammerite Trimetal Nobel Motip BV Akzo Nobel Coatings AG European Aerosols European Aerosols Kurt Vogelsang De Keyn Paint Motip BV Intergamma Motip BV Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Auto-K Motip Leroy Merlin Motip Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH Kurt Vogelsang GmbH
France UK Belgium NL NL NL NL Germany Belgium NL NL NL France France France France France France France France France France France France France France France France France France France France France France France France France NL Belgium NL Germany Germany Germany Germany Germany Germany Germany Germany Germany Germany Germany
2.1. Sampling Slight changes in sampling and measuring conditions were made compared to the former procedure [3]. Paint
was sprayed on microscopy glass slides (SuperFrost Color, Menzel-Gla¨ ser, Germany) from a distance of 0.3 m. The samples were allowed to dry horizontally for 72 h at room temperature. The adhesive tape, mounted on the glass slide
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
prior to spraying in order to transfer the paint samples easily to the XRF sample chamber, was not used anymore. For XRF analysis, paint samples from glass slides were directly collected by scraping with a scalpel and transferring the samples onto a large piece of adhesive tape. This made a simultaneous analysis of several paint samples possible. From each spray paint, three samples were prepared, for shaken as well as non-shaken cans, in order to make a reproducibility study.
63
the resolution was 20 eV per channel; the analysis-area diameter was about 2 mm and the measuring atmosphere was vacuum. Paint samples, with a diameter of 3 mm were transferred to a large piece of adhesive tape (Sellotape Diamond Ultra Clear, Holland) with a scalpel and tweezers. On this tape, around 60 paint samples were collected as depicted in Fig. 1. This piece of tape was mounted on the sample holder of the XRF spectrometer. With a programmable stage positioning, all paint samples were analysed in one sequence.
2.2. Microscopy 2.5. Spectral library and database A microscopic investigation of the coated glass slide was done, using an Olympus BX6O (Japan) microscope with up to 1000 magnification and bright- and dark-field observation. This microscope is equipped with a digital camera AxioCam HR (Carl Zeiss, Germany) to take images of paint surfaces using AxioVision 3.0 (Carl Zeiss) image acquisition software.
All measured IR-spectra were put inside a searchable spectral library using KnowItAll software package (Bio-Rad Laboratories). As properties of each spectrum, the brand, the colour name, the supplier and the country of purchase of the original spray can were given together with the elemental composition measured by XRF. It is possible to run queries using these properties.
2.3. Fourier transform infrared spectrometry (FTIR) An FTIR spectrometer (Nicolet 510P, USA) equipped with a KBr beam splitter, an IR-microscope (NIC-Plan, USA) and a mercury cadmium telluride (MCT) detector was used to analyse the chemical binders and fillers present in these coatings. One hundred scans were collected with a resolution of 4 cm1 and the intensity (% transmittance) versus wave number (cm1) was measured between 650 and 4000 cm1. Paint samples with a diameter smaller than 1 mm were transferred with a scalpel and tweezers to the window of a diamond compression cell (Micro Compression Diamond Cell, SpectraTech, UK). Once compressed, one diamond window with the sample attached was put on the sample stage of the IR microscope for analysis. The obtained spectra were interpreted and compared with our commercial and personal spectral libraries of paint materials. 2.4. X-ray fluorescence (XRF) To analyse the chemical elements present in spray paint coatings, XRF spectroscopy was carried out using a Kevex Omicron (USA) energy dispersive XRF spectrometer. The operating conditions were as follows: the accelerating voltage was 45 kV; the beam current was 0.1 mA; the collection time (life) was 100 s; the energy range/gain was 0–40 keV;
3. Results 3.1. Microscopy In this study, the microscopic analysis was emphasised on the morphologic characteristics of a paint layer. A colour analysis, a (micro-)spectrophotometric measurement, was not made. This kind of measurement requires a perfect homogeneous sample with uniform surface characteristics. These two requirements are often not present in real case spray paint samples. The influence of external circumstances on the surface characteristics is too high. Paint support can be rough or absorb paint leading to the absence of a uniform paint layer. Furthermore, coatings from non-shaken cans tend to be more brittle and get loose of the substrate than those emanating from rigorously shaken cans. All these variations hamper a comparative colorimetric study. In this microscopic analysis, the following types of paint were distinguished: mat, satin, brilliant and metallic. A metallic paint presents more characteristic elements, such as shape and distribution of the metallic particles, than the other three types that are distinguished by their difference in roughness of the surface (mat > satin > brilliant). An example of this difference in surface characteristics is illustrated
Fig. 1. Adhesive tape with 60 red spray paint samples for XRF-analysis.
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F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
Fig. 2. Different types of a red spray paint (Dupli Color, flame red RAL 3000) at 100 magnification and bright field observation (scale bar: 100 mm).
Table 2 Groups formed by infrared analysis with list of binder, filler and pigment composition and presence in this paint collection Group
Binder/filler/pigment composition
Presence as number of spray paints
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Alkyd–styrene Alkyd–magnesium silicate Alkyd-monoazo (CI Pigment Red 112) Alkyd–monoazo (CI Pigment Yellow 74) Alkyd–nitrocellulose Acrylic–alkyd Acrylic Acrylic–urethane–styrene-monoazo (CI Pigment Red 254) Acrylic–isophtalic–alkyd Acrylic–quinacridone (CI Pigment Red 122) Acrylic–perylene (CI Pigment Red 178) Acrylic–styrene Acrylic–magnesium silicate Mica–poly(dimethylsiloxane)-perylene (CI Pigment Red 178) Polyvinylacetate Styrene–epoxy–magnesium silicate Orthophtalic alkyd–calcite
1 1 8 4 23 2 1 1 1 1 1 2 1 1 1 1 1
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in Fig. 2. The results of this investigation were not taken into consideration for discrimination purposes. Our investigation shows that only a uniform surface is obtained by reproducible spray conditions. This is of major importance to compare questioned samples. 3.2. FTIR When comparing three spectra from spray paint coming from the same spray can made under the same conditions
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(shaken or non-shaken), only very little spectral differences were observed. The existing differences, fluctuation of the baseline, can be explained by the experimental conditions, i.e. the geometry of the paint particle on the diamond window. Internal reflections between sample and diamond window cause changes of the beam intensity at different wavelengths, changing the baseline position. The intravariability of these spectra is very low. Major differences exist between spectra of spray paints coming from shaken and non-shaken cans of the same paint.
Fig. 3. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 1–5).
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These differences are observed in the fingerprint region of the spectrum. Some absorption peaks of ‘‘shaken’’ paint samples are not present in ‘‘non-shaken’’ paint samples. These peaks present in ‘‘shaken’’ paint samples only are of weak intensity. Indeed, in a non-shaken spray can, certain paint components settle down more preferably than others. When spraying, paint from the bottom of the spray can is pushed out at first. Paint samples under ‘‘non-shaken’’ condition, contain less material from the top of the spray can. In an IR spectrum, the specific absorbencies of these top
components are of a too low intensity to be observed or are overlapped by very intense absorbencies of components present in high quantities. A paint sample coming from a shaken can contains a higher quantity of the top components, due to a perfect homogenisation. This is observed in this infrared analysis: a spectrum from a shaken paint sample always contains the same peaks or more peaks than a spectrum from a non-shaken paint sample. For further analysis, the best spectrum (little noise, small baseline fluctuations) from each shaken paint sample was
Fig. 4. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 6–10).
F. Govaert, M. Bernard / Forensic Science International 140 (2004) 61–70
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Fig. 5. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 11–15).
selected. These 51 selected spectra were compared one to another. This comparison permitted to form 17 groups according to binder type, filler and pigment composition. Table 2 lists the results of this comparison together with the typical binders, fillers or pigment components and the presence in this spray paint collection. Figs. 3–6 show infrared spectra of these 17 groups and illustrate that the typical characteristics can be clearly observed.
On basis of this distribution, the discriminating power (DP) of infrared analysis of spray paints was calculated according to Smalldon and Moffat [5], where: Number of discriminating pairs DP ¼ (1) Number of possible pairs or; DP ¼ 1
2M NðN 1Þ
(2)
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Fig. 6. Infrared spectra, absorbency vs. wave numbers (cm1), of typical spray paints according to Table 2 (groups 16 and 17).
with M the number of matching pairs and N the total number of analysed spray paints in the collection. Infrared analysis of this paint collection has a discriminating power of: M ¼ 289 and N ¼ 51
(3)
DP ¼ 0:773:
(4)
3.3. XRF The results of the X-ray fluorescence analysis of spray paints show more variations depending on the homogeneity of the paint inside the spray can when spraying. Indeed,
some quantitative and qualitative differences of chemical elements were observed between coatings emanating from shaken and non-shaken spray cans. As Zeichner et al. [1] described, coatings from non-shaken cans tend to contain higher concentrations of detectable chemical elements than coatings from shaken cans. This tendency was observed in this study as well. A qualitative analysis shows differences between shaken and non-shaken cans. Fig. 7 illustrates the comparison of shaken and non-shaken spray cans. A difference at one-element level is more frequent than no difference. The number of sprays that present a difference at two-, three- or four-element level decreases very fast. In each of
Fig. 7. Comparison of the elemental composition of a spray paint between shaken and non-shaken paint samples.
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Fig. 8. Presence (%) of chemical elements in paint collection.
these categories (one, two and three elements), the distribution of different elements was observed. When one or two elements are different, there are generally more elements detected in non-shaken samples than in shaken samples. In the category where three or four elements are different, there are not enough sprays to draw the conclusions. For discriminating purposes, the groups formed by infrared analysis were taken and those spray paints that are not discriminated with this method were compared according to the elemental composition, measured by XRF. A further discrimination is possible when the elemental composition of the sprayed paint is analysed. All measured chemical elements and their presence (%) in the spray paint collection are depicted in Fig. 8. FTIR followed by X-ray analysis permits to form 37 groups in total, with a maximum of four sprays in one group. The discriminating power of this sequence, FTIR followed by XRF, for the analysis of red spray paints was calculated according to Eq. (2) with: M ¼ 15 and N ¼ 51
(5)
PD ¼ 0:988:
(6)
4. Discussion The analysis sequence, infrared analysis followed by Xray fluorescence, proved to be successful to discriminate red spray paints. With a discriminating power of 0.988 a satisfying result was obtained. Only the instrumental analysing techniques were considered for differentiation purposes. Red spray paints present more different compositions than black paints [3]. Infrared analysis permits to classify
these paints into 17 different groups (only 6 out of 40 for black paints). Almost half of the red spray paints are composed of alkyd-nitrocellulose-based binders. To distinguish between spray paints with this type of binder system, a further analysis technique is absolutely necessary. This is obtained with the help of X-ray fluorescence. Twenty-one different chemical elements were analysed by X-ray fluorescence. The most frequent elements in this red spray paint collection are Ti (94%), Fe (84%), Ca (80%) and to a lesser extent Cl (64%), Zn (52%) and Si (46%). After X-ray fluorescence analysis, a group with a maximum of four non-differentiating paints was obtained. These four paints origin from the same supplier, but represent different colours. The same conclusion can be made for groups with three paints. Only in one group of two non-differentiating paints, two different brands were encountered. In this case (Leroy Merlin) the original manufacturer is unknown, but also here, the two colours are different. An additional colour analysis, i.e. spectrophotometry, could be very useful to discriminate these paints provided that a uniform surface is present. The searchable spectral library contains now the infrared spectra and the additional information of black and red spray paints, analysed at the Belgian Forensic Institute. Cooperating European colleagues are putting samples at our disposal for further analysis and consequently to fill up the database. A CD-ROM of this database will be distributed to interested forensic institutes. Acknowledgements This work was carried out during a work placement supported by the IPSC, University of Lausanne, Switzerland.
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The authors are grateful to the German Forensic Science Institute, Bundeskriminalamt, for delivering paint samples from spray paints. References [1] A. Zeichner, N. Levin, E. Landau, A study of paint coat characteristics produced by spray paints from shaken and nonshaken spray cans, J. Forens. Sci. 37 (1992) 542–555.
[2] C.D.J. Krausher, Characteristics of aerosol paint transfer and dispersal, Can. Soc. Forens. Sci. 27 (1994) 125–142. [3] F. Govaert, G. De Roy, B. Decruyenaere, D. Ziernicki, Analysis of black spray paints by Fourier transform infrared spectrometry, Probl. Forens. Sci. 47 (2001) 333–339. [4] B. Caddy, Forensic Examination of Glass and Paint, Analysis and Interpretation, Taylor and Francis, London, 2001. [5] K.W. Smalldon, A.C. Moffat, The calculation of discriminating power for a series of correlated attributes, J. Forens. Sci. Soc. 13 (1973) 291–295.