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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.

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Presentation on theme: "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."— Presentation transcript:

1 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.

2 Motivation How would you analyze the paint chip displayed? List at least 4 observable characteristics.

3 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)

4 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 186- 192 Explain how microscope analysis helped solve the Lindbergh kidnapping

5 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

6 Paint is an example of trace evidence Analyzed by: –Layers of a chip –Ingredients –Custom coloring chromatography

7 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

8 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

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10 Which layer of paint is most informative? Undercoat more than any other property, gives paint its most distinctive forensic characteristics. contains most pigment

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12 Each layer is unique Top coat, primer and undercoat all have different chemical compositions Exposure to chemicals, dirt and rain can complicate analysis

13 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.

14 Are these paintings the same or is one forged? How can you tell? Explain in detail.

15 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

16 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

17 DO NOW answer Undercoat more than any other property, gives paint its most distinctive forensic characteristics. contains most pigment

18 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. HortonThrift Store Masterpiece? believes her painting is worth about $50 million Some experts disagree. Is it or isn't it? How would you tell?

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20 How would you determine if a painting is real or fake?

21 How would you collect paint samples from a crime scene?

22 Video showing Tower Bridge paint analysis | Tower Bridge

23 How would you collect samples of paint at a crime scene?

24 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

25 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

26 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

27 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.

28 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

29 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?

30 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

31 Different paints yield different color results

32 Assessment How would you collect a paint sample from a car which is suspected of a hit and run?

33 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

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35 By matching the paint trace (on the glass slide) to known samples, the exact color can be found.

36 Stereoscopic microscopic analysis of paint

37 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

38 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

39 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

40 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

41 YouTube - Chromatography

42 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

43 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

44 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?

45 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!

46 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?

47 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

48 Assessment How is micro-spectrophotometry similar to gas chromatography? They both separate a paint sample into each color it is composed of.

49 AIM: How can we separate paint chips based on their molecular structure? DO NOW: Explain the difference in how the stereoscopic microscope and the Micro- spectrophotometry separate paint chips. Homework: Study for quest tomorrow

50 Motivation Create a list: Why do we even want to analyze paint chips?

51 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

52 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


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