Monday March , 2013
• AIM: How does the forensic
examination of paint give insight to
solving a crime scene?
DO NOW: How does microscopic analysis help
investigate forensic evidence?
Homework: Text Read pages 219-222 Forensic
analysis of paint. Answer the following
1- What is the function of a binder?
2- What happens to the paint after applied to the
surface?
3- What is one of the most common types of paint
examined in a crime lab?
4- List and describe the 4 organic coatings applied to
automotive steel.
Motivation
• How would you
analyze the paint chip
displayed?
• List at least 4
observable
characteristics.
PAINT:
• Coating consisting of
– Pigments
– a polymeric film former (binder)
– a suspending medium or solvent
• 3 classes of paint
– Oil based
– Water based
– Solvent based ( varnish)
Tuesday 3/5/13
• AIM: How does a paint mixture break
down?
• DO NOW: How does the forensic
examination of paint give insight to
solving a crime scene?
HOMEWORK: Textbook read pages 186192 Explain how microscope analysis
helped solve the Lindbergh kidnapping
Paint is an example of trace
evidence
• Transferred by:
– Car accidents
• Car-car
• Car-victim
– Wet paint leaving a mark or imprint
– Microscopic transfer on to a tool used to
commit a crime
• Ex: crobar used to break open a door
Paint is an example of trace
evidence
• Analyzed by:
– Layers of a chip
– Ingredients
– Custom coloring
• chromatography
Paint is a mixture
• Pigment (color)
– Blues and greens are organic
– Reds, yellows, whites: inorganic
• Modifiers (change pigment)
– Control the property of the paint
• Gloss, flexibility, durability,
toughness
• Extenders (keep pigment)
– Add bulk and covering capacity
– Inorganic
• Binders (help paint stick to the
surface)
– Natural or synthetic
– Stabilizes the mixture
– Forms a film when spread
Automobile Coatings or Layers of paint
• Electrocoat Primer – the first layer applied to
the steel for corrosion resistance.
• Primer surfacer – smooths out and hides
imperfections
• Basecoat or Undercoat – provides color and
represents the “eye appeal” of the finish
• Clearcoat or topcoat – resists UV radiation and
acid rain
Which layer of paint is most
informative?
• Undercoat more than any other
property, gives paint its most
distinctive forensic characteristics.
• contains most pigment
Each layer is unique
• Top coat, primer and undercoat all have
different chemical compositions
• Exposure to chemicals, dirt and rain can
complicate analysis
• A man was killed by riding his bike late one
night. The defendant was charged with failure to
stop at the scene of a serious personal injury
accident. As a forensic scientist how do you
think the defendant was caught.
• Are these paintings the
same or is one forged?
How can you tell?
Explain in detail.
In your groups hand in only 1 sheet
• 1- Place your heading listing ALL group members
• Questions:
1- What is the crime?
2- List some of the initial evidence found by the police
3- What did the witnesses say?
4- What kind of car did John Vollman drive?
5- How was Vollman found guilty?
6- What information was gathered by the autopsy?
7- Define NAA
8- How did the NAA help solve this case?
9- What year did Vollman get convicted
Wednesday 3/6/13
• AIM: How does a paint mixture break
down?
• DO NOW:Which layer of car paint is the
most informative and WHY?
• Homework: Textbook Read page 219-223
Answer questions 36-43 on page 231.
Write out the question followed by the
answer
DO NOW answer
• Undercoat more than any other
property, gives paint its most
distinctive forensic characteristics.
• contains most pigment
Motivation
• Thrift Store Masterpiece?
Teri Horton, a retired truck
driver, talks with CNN's
Anderson Cooper about a
painting she bought years
ago that she believes is the
work of famed painter
Jackson Pollock. Horton
believes her painting is worth
about $50 million Some
experts disagree.
Is it or isn't it? How would
you tell?
How would you determine if a
painting is real or fake?
How would you collect paint
samples from a crime scene?
Video showing Tower Bridge
paint analysis | Tower Bridge
How would you collect samples
of paint at a crime scene?
London tower bridge
• built in 1894
• Extract paint chip samples by first placing a piece
of masking tape over an area, smacking it with a
chizzle then remove the tape
• Helps to establish each layer as undercoat, primer,
finishing coat etc.
• Layers of dirt defines the upper layer of finish coat
– Also tells you about the environment the paint was
exposed to
• 1956 clean air act: no dirt layer
London bridge tower continued
• Dirt helps to determine the time frame of
the layer
• Comparing layers allows to determine how
the bridge looked and was changed through
out history
Collecting paint from a crime
scene
• Found on a variety of objects
–
–
–
–
Clothing
Vehicles
Tools
Furniture
• Mixed with dirt or grease
• Undermost layer is the most informative
• Matching chips with flakes individualize evidence
therefore preservation is extremely important
• Use of dental drills and scalpals are the most often
used tools
Thursday 3/7/13
• AIM: How can we
analyze each layer of a
paint sample?
• Homework: Textbook
read page 201 Case
analysis answer the
questions on the next
slide
DO NOW:List at least 5
characteristics you would use if
this paint chip was found at a
crime scene.
Paint analysis
• Narrow down a paint sample to the year,
make and model of production
• Find the factory that produced the paint and
the dealership it was first sold
Thursday 3/7/13
• Homework: Textbook read page 201 Case reading
the central park rapist
• Question 1- Who were the original suspects in this
case and why were they suspected of the rape?
• Question 2- What did the forensic analyst in this
case testify to?
• Question 3- Even though semen samples did not
match, why were the suspects convicted?
• Question 4- Who was the central park rapist and
how was he caught?
Paint: inorganic and organic
• Causes different chemical
analysis of different types
and colors of paint chips.
• Microscope: traditional
and most important in
locating and comparing
paint specimens
– Analysis at 10-40 times
magnification reveals paint
layers
– Identifies each individual
layer
Different paints yield different
color results
Assessment
• How would you collect a paint sample from
a car which is suspected of a hit and run?
Paint chip and flake analysis
• The number of layers is determined by
variety of microscopic technique
• Compare flakes to known or control
samples easiest technique is to match
fractured edges to an area of paint loss
• Investigators use light microscopes,
stereomicroscopes and sometimes scanning
electron microscopes to look for jigsaw fits
By matching the paint trace (on the glass slide) to
known samples, the exact color can be found.
Stereoscopic microscopic
analysis of paint
Analysis of paint
• Stereoscopic microscopes
– Compare known specimens
• Color
• Surface texture
• Color laying sequence
– Layers of different colored paint are very
helpful in matching an unknown to a known
sample
Analysis of paint
• Micro-spectrophotometry
– Helps determine nature of
pigments by reflecting light
through them
– Infrared spectrometry:
determines organic
components
– X-ray powder diffraction
determines microcrystalline
components
• Top four: cross
sections of different
samples and
underlying layers of
red paint of different
red automobiles
• Bottom Four: cross
sections of common
red household paint
Pyrolysis
•
•
•
•
Pyro: Fire
Lysis: to break
Gas chromotography
Chromotography:
separates paint according
to color
• Paint is vaporized and
injected into a gas
chromotograph which
separates paint into its
components
YouTube - Chromatography
Mass spectrometry
• Separates paint chip
components based on
molecular weight
• Each pigment has a
different molecular
weight
• Creates a chemical
fingerprint that can
be compared to
reference samples
Royale Canadian Mounted Police
• Created a database called Paint Data Query
– Contains chemical composition of paint from
most vehicles sold in North America after 1973
– International database
– Used by forensic scientists to test unknown
samples found at crime scenes
– FBI: has a similar database of more than 40,000
paint samples
Thursday 3/7/13
• Homework: Textbook read page 201 Case reading
the central park rapist
• Question 1- Who were the original suspects in this
case and why were they suspected of the rape?
• Question 2- What did the forensic analyst in this
case testify to?
• Question 3- Even though semen samples did not
match, why were the suspects convicted?
• Question 4- Who was the central park rapist and
how was he caught?
Last night homework answers
1- 5 teens were arrested because they were
walking out of the park around the time of
the rape
2- hair fibers on the teens clothes match those
found on the victim
3- Hair fibers match
4- Matair Reyes was found to be the central
park rapist because his semen sample
matched!
Text read pages 260-261 in your
notebook write out and answer
• Who are the suspects?
• What are the crimes?
• What are the pieces of evidence at each crime
scene?
• When and what was the major break in the case?
• What roll did paint play in the capture of the
suspects?
• How were all the crimes connected?
Textbook read pages 260-261
• James Tyler Williams and Benjamin
Mathew Williams
• June 18,1999- Burned synagogues
• July 1, 1999- Killed a gay couple Gary
Matson and Winfred Mauder
• March 2 1999- Medical abortion building
arson
•
Assessment
• How is micro-spectrophotometry similar to
gas chromatography?
• They both separate a paint sample into each
color it is composed of.
• AIM: How can we separate paint chips
based on their molecular structure?
• DO NOW: Explain the difference in how
the stereoscopic microscope and the Microspectrophotometry separate paint chips.
• Homework: Study for quest tomorrow
Motivation
Create a list: Why do we even want to
analyze paint chips?
Monday 5/7/12
• AIM: How can paint chips be chemically
broken down into different colors?
• DO NOW: List some characteristics of
paint that help to individualize it
• Homework: Study for TEST on
WEDNESDAY
Friday 5/4/12
• AIM: How can forensic scientists
physically separate paint chip samples?
• DO NOW: textbook page 258-259. Read
the lab and answer questions 4 and 5 in your
notes
• EXAM TUESDAY CHAPTER 8. check
the website for review topics