LECTURE 17: PAINT AND GLASS

Question 1

automotive paint

Answer 1

1. Electrocoat primer on metal surface for anti-corrosion
2. Primer surfacer to make surface smooth
3. Basecoat where pigments added
4. Clearcoat to protect everything below

Question 2

Can be individual/group evidence - paint evidence

Answer 2

• specialised coatings will have specific make-up
• individual manufacturers may have different formulations even for the same colour
• need to be aware that car manufacturers may use number of companies for supplies/use same paint on number of models

Question 3

Destructive testing - art fraud

Answer 3

• Spot tests – for particular pigments
• Scrape off sample and do a chemical reaction to test for
• particular elements
• e.g. Naples Yellow Pb(SbO4)2H2
• Massicot PbO
• Lead-tin Yellow 2PbO.SnO2 used in Europe < 1750
• Crystal size/ structure

Question 4

Semi Destructive - art fraud

Answer 4

• Laser microanalysis AES
• Fine laser beam ~ 100 µm across focussed on specimen and material evaporated
• Get small indents in metallic objects but quite large in ceramics, glass, organic materials

Question 5

Non-Destructive - art fraud

Answer 5

• radiocarbon dating
• thermoluminescence (dating of fired objects)
• neutron autoradiography
• SEM to look at pigment particle shape/size
• Spectroscopic techniques
• X-ray
• infra red (IR)

Question 6

float glass

Answer 6

• flat surface on both sides, used for windows

Question 7

glass evidence is usually what kind of evidence

Answer 7

class evidence

Question 8

analysis of glass

Answer 8

refractive index and density

Question 9

glass fractures are

Answer 9

concentric and radial fractures

Question 10

paint

Answer 10

a suspension of pigments & additives intended to colour or protect a surface.

Question 11

pigment

Answer 11

is a fine powder, insoluble in the medium in which it is dispersed – the granules don’t dissolve & remain intact & are dispersed evenly across the surface. They may be organic, inorganic, or a mixture.

Question 12

solvents

Answer 12

dissolve the binder & give the paint a suitable consistency for application (brushing, spraying, etc).

Question 13

binders

Answer 13

is the portion of the coating, other than the pigment, that allows the pigment to be distributed across the surface.

Question 14

vehicle

Answer 14

refers to the solvents, resins, & other additives that form a continuous film, binding the pigment to the surface. Used interchangeably with “binder”

Question 15

paints are divided into 4 categories

Answer 15

1. Architectural paints (household paints) = coatings most often found in residences
   & businesses
2. Product coatings = applied in the process of manufacturing products include
   automobiles. 2nd major category
3. Special-purpose coatings = fulfil some specific need beyond protection or
   aesthetic improvement, such as skid resistance, water proofing,
   or luminescence.
4. Art paints = similar in many respects to architectural paints, but
   many artists formulate their own paints, leading to potentially unique sources.

Question 16

microscopes used for paint

Answer 16

polarised light microscopy for layer structures
infrared (IR) spectroscopy for binder, pigments and additives
Raman spectrocopy based on light scattering rather than absorption
pryrolisis-gas chromatography disassembles molecules through heat (pyrolysis), uses the breakdown products for comparisons of paints & identification of the binder type.
energy dispersive X-ray spectrometer (SEM/EDS) is used to characterise the structure & elemental composition of paint layers, uses an electron beam rather than a light beam.

Question 17

soil and glass are usually

Answer 17

class evidence

Question 18

soil =

Answer 18

earth material, either natural or manmade that is transferred from a crime scene to a person or object or vice versa

Question 19

glass can be defined as an

Answer 19

amorphous solid

Question 20

mechanical fit or fracture match

Answer 20

• There is one set of circumstances where glass can be individualized to a particular object.
  occurs where a piece of glass breaks into relatively large pieces that have at least one, good, intact edge that can be fitted to the edge of another piece from the same source // large pieces can be put together like a jigsaw puzzle, so the evidence can be individualized to a particular source.

Question 21

examination of small glass partciles

Answer 21

density and refractive index

Question 22

density

Answer 22

sink/float method

Question 23

refractive index is the

Answer 23

ratio of the velocity of light in a vacuum to the velocity as it passes through the medium

Question 24

becke line immersion method

Answer 24

• When a piece of glass is immersed in a liquid of different refractive index & observed under a microscope with transmitted light, a bright halo in the shape of the glass, will appear to surround the glass. This halo is called the Becke line, caused by the difference in refraction.
• If glass & liquid have the same refractive index, the Becke line will disappear.