paint-examination.pptx

1. THE USE OF MICROSCOPY,
SPECTROSCOPY AND
CHROMATOGARAPHY
TECHNIQUES FOR PAINT
EXAMINATION
Sanjeev S Koni
Assistant Professor
Centurion University of
Technology and
Management.

2. INTRODUCTION
 The analysis of paint samples is often required in the
Forensic Science Laboratories.
 These samples come from variety of sources such as motor
vehicles in Hit-Run cases and door and windows in
breaking and entry cases.
 The analytical problems facing the forensic scientist is
the comparison of paint samples located during the course
of an examination, with samples obtained from the possible
sources to establish the common source of origin.

3. COMPONENTS OF PAINT
 Paint is commonly known as pigmented coating.
 The main components of Paint are:
1. Pigment
2. Binder
3.Solvent
4. Additives.

4. ROLE OF COMPONENTS
Pigment:
A finely ground, inorganic or organic,
insoluble, and dispersed particle. Besides color, a pigment
may provide many of the essential properties of paint such
as opacity, hardness, durability, and corrosion resistance.

5. ROLE OF COMPONENTS
 The pigments can be classified as natural or synthetic type.
 Natural pigments include clays, calcium carbonate, mica,
silica and talcs while synthetic pigments include
engineered molecules such as precipitated calcium
carbonate and synthetic pyrogenic silica.
 Hiding pigments such as Titanium dioxide, Phthalo blue
and Red iron oxide protects substrate from effects of UV
radiation and make paint opaque.

6. ROLE OF COMPONENTS
Binders:
A nonvolatile portion of the liquid vehicle of a
coating, which serves to bind or cement the pigment
particles together .
 It includes synthetic or natural resins such as cement
alkyds, vinyl-acrylics, vinyl acetate ethylene
(VAE), polyurethanes, polyesters, melamine, resins or oils.

7. ROLE OF COMPONENTS
Solvent:
The main function of solvent is to adjust the curing
property of the viscosity of the paint.
 It controls flow and application properties, and affects the
stability of the paint while in liquid state.
 Its main function is as the carrier for non volatile
components.
 Petroleum distillate, Esters , Glycol ethers are used as
solvents.

8. ROLE OF COMPONENTS
Additives[Modifier]:
Any substance that added in small quantities
to improve the properties of paint are called additives.
 Additives may include substances such as driers, corrosion
inhibitors, catalysts, ultraviolet absorbers, and plasticizers.

9. AUTOMOBILE PAINTS
Coating :
A generic term for paint, lacquer, enamel, or other
liquid or liquefiable material that is converted to a solid,
protective, or decorative film or a combination of these
types of films after application.
 Automobile finishing has at least four coatings:
1. Electro coat primer 2. Primer Surfacer
3. Base coat 4. Clear coat.

10. LAYERS OF COATING

11. ELECTROCOAT PRIMER
 They are epoxy-based resins electroplated on to surface to
prevent corrosion
 They are uniform in color. They are first layer. They are
usually black or grey in color.

12. PRIMER SURFACER
 Originally intended for corrosion control before base coat.
 It smoothes out e or hides imperfections or seams.
 Color pigments are used to prime for color.
Ex. Gray used for pastels
Red oxide used under dark colors

13. BASE COAT
 Base coat is the pigment that provides appearance of the
finish.
 Integrity depends on its ability to resist weather, UV
radiation, and acid rain
 Acrylic based polymer comprises binder.
 Heavy metals like lead and chrome no longer used. In
favor now is organic based pigments.

14. CLEAR COAT
 They are unpigmented coat used to improve gloss,
durability, and appearance.
 Most of them are acrylic based
 Polyurethane clear coats are becoming more popular.
 It offers great resistance and gives good appearance.

15. PHYSICALAND CHEMICAL
FEATURES OF PAINT
 Paint films are characterized by number of physical and
chemical features.
 The physical characteristics may include color, layer
sequence, thickness, surface and layer features,
contaminants and weathering.
 Chemical components may include pigments, polymers
and additives.
 These features can be evaluated by various chemicals and
instrumental methods.

16. SAMPLE PREPARATION AND
LAYER ANALYSIS
 The layers in a paint film are identified by viewing the
sample edges at magnifications ranging between 5× and
100×.
 Definitive paint layer identification usually requires sample
preparation techniques such as manual or microtome
sectioning, edge mounting and polishing, or both.
 A combination of techniques may be required to fully
characterize the layer structure.
 The extent of sample manipulation and preparation will
depend on the amount of paint available and its
characteristics.

17. SAMPLE PREPARATION AND
LAYER ANALYSIS
 Paint layer structure can be observed by using a scalpel blade to
make an oblique cut through a sample. The larger surface area
created by this angled cut may enhance layer visualization and
assist in the detection of layer in homogeneities.
 The preparation of thin-sections and the separation of paint layers
can be accomplished with a scalpel blade. Preliminary solvent tests
can be conducted on the manually prepared sections and layer
fractions.
 Subtle differences in color, pigment appearance, surface details,
inclusions, metallic and pearlescent flake size and distribution, and
layer defects may require microscopical comparisons of the edge,
oblique cut, and surface views of known and questioned paint
samples. These comparisons must be carried out with both samples

18. GUIDE TO MOTOR VEHICLE
IDENTIFICATION

19. PAINT SAMPLE GUIDE

20. TECHNIQUES EMPLOYED.
 For the examination of paint, the following instrumental
techniques are applied.
1. Microscopy.
2. Spectroscopy.
3. Chromatography.

21. MICROSCOPY
 Following microscopic techniques are used to analyze the paint
samples.
1. Polarized Light Microscopy[PLM]
2. Scanning Electron Microscopy[SEM]
3. Transmission Electron Microscopy[TEM]
4. Optical Light Microscopy.

22. POLARIZED LIGHT
MICROSCOPY [PLM]
 Polarized Light Microscopy is appropriate for the examination of
Layer structure as well as for the comparison or identification of
particles present in a paint film including pigments, extenders,
additives, and contaminants.
 Extenders and other components of a paint film are generally of
sufficient size to be identified by their morphology and optical
properties using this technique.
 Particles to be examined are generally 1-20 μm – smaller than one
thousandth of a millimeter. Each type of pigment reacts differently to
these polarized light rays so that every single particle can be identified.

23. POLARIZED LIGHT
MICROSCOPE

24. POLARIZED LIGHT
MICROSCOPY [PLM]
Pigments under Polarized Light
Mineral Debris in paint under
Polarized Light

25. SCANNING ELECTRON
MICROSCOPE

26. SCANNING ELECTRON
MICROSCOPY
 Scanning electron microscopy-energy dispersive X-ray analysis (SEM-
EDS) can be used to characterize the morphology and elemental
composition of paint samples.
 The SEM raster an electron beam over a selected area of a sample,
producing emission of signals including X-rays, back scattered
electrons, and secondary electrons. Emitted X-rays produce
information regarding the presence of specific elements, and the
electron signals produce compositional and topographical visualization
of a sample.
 The depth from which X-rays are produced (the analytical volume) is
dependent upon beam energy, composition and density of the sample,
and energy of the X-rays.

27. SCANNING ELECTRON
MICROSCOPY
After a hit and run accident, often
small car paint flakes can be found at
the crime scene. Car paint consists out
of different layers of paint.
Comparisons are made between flakes
from a suspect vehicle and the
specimen in order to find a match.
The picture shows a paint flake
revealing various paint layers.

28. TRANSMISSION ELECTRON
MICROSCOPE

29. TRANSMISSION ELECTRON
MICROSCOPY
 With an electron microscope, featuring electromagnetic
lenses and special detectors, it is possible to examine very
small particles.
 In a Transmission Electron Microscope, electrons are
speeded up in a vacuum until their wavelength is extremely
short.
 Beams of these fast-moving electrons are focused on an
extremely thin paint sample which absorbs or scatter them,
there by forming an image of particles in the sample.

30. TRANSMISSION ELECTRON
MICROSCOPY
 A TEM can achieve the magnification factor of approximately
one million making possibly to view an object as small as atom.
 This sample is approximately 12 microns. This reveals that the
paint chiefly consists of evenly dispersed extremely fine white
pigment particles in binding medium.

31. OPTICAL LIGHT MICROSCOPY
 To study the uppermost layer of a painting, researchers use
an optical microscope.
 There are various kinds of microscope available, ranging
from small models giving 3x to 10x magnification to large
instruments with magnification factors of up to 50x.
 The microscope lenses enable the condition and certain
physical aspects of the painting to be assessed, revealing
details of the brushwork, the kinds of pigments used, the
texture of the paint layer, restorations and damage.

32. OPTICAL LIGHT MICROSCOPY

33. SPECTROSCOPY
 Following microscopic techniques are used to analyze the
paint samples.
1. Vibrational Spectroscopy [IR Spectroscopy]
2. X-Ray Fluorescence Spectroscopy
3. Microspectrophotometry
4. Raman Spectroscopy

34. VIBRATIONAL SPECTROSCOPY
 Infrared spectroscopy (IR) may be used to obtain
information about binders, pigments, and additives used in
various types of coating materials. Because the paint
fragments to be analyzed are often quite small, a beam
condensing or focusing device is normally required, and a
Fourier transform infrared (FTIR) spectrometer is
recommended.
 Both transmittance and reflectance techniques may be
used for the analysis of coatings, but in most cases,
transmittance methods are preferred because all the
sampling wavelengths are subjected to the same path
lengths and most of the reference data of coatings, binders,
pigments, and additives consist of transmittance spectra.

35. VIBRATIONAL SPECTROSCOPY
 In addition, transmittance data are not significantly affected by
collection parameters such as type of refractive element used,
angle of incidence chosen for analysis, or the degree to which the
sample makes contact with the refractive element. These factors
affect spectra obtained using internal reflectance methods.
 If a multiple-layer coating system is to be subjected to an
infrared examination, optimal results can be obtained if each
layer is isolated and analyzed separately.
 Methods that use solvents to assist in the sample preparation
should be used with caution because they might alter the sample
or result in the production of residual solvent spectral
absorptions.

36. VIBRATIONAL SPECTROSCOPY
Spectrograph of 3 different
layers.
Layer-1 : Protective coating.
Layer-2: Base coat and poly propylene
polymer
Layer-3: Binder layer.

37. X-Ray Fluorescence
Spectrometer

38. X-Ray Fluorescence
Spectroscopy
 XRF is an elemental analysis technique based upon the
emission of characteristic X-rays following excitation of the
sample by an X-ray source.
 XRF analysis is less spatially discriminating than SEM-
EDS because of its larger analytical beam size and the
greater penetration depth of X-rays compared to electrons.
 However, the limits of detection for most elements are
generally better than for SEM-EDS, and the higher energy
X-ray lines produced by higher energy excitation typical of
XRF can be useful during qualitative analysis.

39. X-Ray Fluorescence
Spectroscopy
 Because of the significant penetration depth of the primary
X-rays, XRF analysis will generally yield elemental data
from several, if not all, layers of a typical multilayer paint
fragment simultaneously.
 Because variations in layer thickness may cause variations
in the X-ray ratios of elements present, this technique can
be used only comparatively or qualitatively.

40. X-Ray Fluorescence
Spectroscopy
X-Ray Spectroscopy Sheds
Light on Leonardo da Vinci’s
Faces

41. MICROSPECTROPHOTOMETER

42. MICROSPECTROPHOTOMETRY
 Microspectrophotometry may be required to provide
objective color data for paint comparison because of the
typically small size of samples.
 The technique can be applied to the outer surfaces of paint
films by diffuse reflectance (DR) measurements with
visible spectrum illumination.
 Diffuse reflectance measurements of paint surfaces are
affected profoundly by surface conditions such as
weathering, abrasion, contamination, and texture.

43. MICROSPECTROPHOTOMETRY
 This fact can provide useful discriminating information
when an examiner is faced with distinguishing different
surfaces that were originally painted with the same paint
formulation.
 Careful reference sampling is essential to the success of
color comparisons of such surfaces.
 Diffuse reflectance techniques can also be used on the
edges of thin paint layers much as it is on outer paint
surfaces.

44. MICROSPECTROPHOTOMETRY
 Before analysis, questioned and known samples can be
mounted side by side on edge and polished to a smooth
surface using a polish of 3-micron grit size or less.
 The requirement for consistent surface finish
characteristics for all samples is achieved easily if the
known and questioned samples are mounted and prepared
in a single mount.
 When required for the discrimination of similarly colored
paint layers, the surface finish of a polished sample must
approach the size of the smallest pigment particles present.

45. RAMAN SPECTROMETER

46. RAMAN SPECTROSCOPY
 Raman spectroscopy is not yet used for routine paint
examination, but it has many potential benefits, particularly the
speed in which it can be applied and the fact that it is a non-
invasive method that can be used to screen paints of all types.
 This focuses on discriminating single layer white architectural
paint.
 The white paint samples varied in manufacturer and finish
(gloss, matt, satin), but were all nominally “pure white”.
 The samples were prepared according to the manufacturers’
instructions, painted onto fresh aluminum surfaces (1 cm2).

47. RAMAN SPECTROSCOPY
 The Raman Spectrograph of White paint samples .
Three Raman Paint
Spectrograph.

48. RAMAN SPECTROSCOPY
 The major advantage of Raman approach is the high
reproducibility in spectra which allows even a small
difference in relative intensity [rather than simple absence
or presence of features ] to be used in discriminating
different samples.
 Raman spectroscopy is rapid technique that gives
information regarding both binder and inorganic
constituents.

49. PYROLYSIS GAS
CHROMATOGRAPHY

50. CHROMATOGRAPHY
 The most common chromatographic techniques employed
for analysis of paints is Pyrolysis Gas Chromatography.
 Automobile paints are analyzed by this techniques.
 Automotive finishes are highly complex polymer systems
made of multiple layers of copolymers, each formulated to
perform a specific function.

51. CHROMATOGRAPHY
 The inclusion of inorganic compounds such as oxides of
metals and aluminum particles for opacity and visual effect
make the finished product difficult to analyze using
standard laboratory instruments.
 They may, however, be analyzed by gas chromatography
mass spectrometry with the addition of a pyrolyzer at the
GC-inlet.
 Pyrolysis reduces the polymeric content of the paint to
volatiles compatible with gas chromatography and mass
spectrometry, leaving the inorganic constituents behind.

52. CHROMATOGRAPHY
 The paints used for automobiles usually include familiar
polymer monomers such as methyl methacrylate, styrene,
butyl acrylate and butyl methacrylate.
 The presence or absence of specific monomers helps
distinguish one paint from others, as does the relative
amounts of the monomers common to two paints. It also
helps in determining approximate age of paints.

53. CHROMATOGRAPHY
Total Ion Chromatogram
resulting from the pyrolysis of a
paint sample at 750 °C for 15
seconds.
Mass spectrum of peak number
7 from the pyrogram shown in
Figure 1, identified as
hydroxypropyl methacrylate.

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