Materials List:



Introduction:

Paint is ubiquitous, it is useful, and it looks nice. It is also a frequently overlooked part of many forensic curriculums. But this doesn’t have to be; paint chips are easier to make and analyze than many people believe. Your students will be engaged, your supervisors will be impressed (should they stop by), and you’ll wonder why you didn’t do this earlier.

Paint is a heterogeneous mixture of organic and inorganic components found on many common items. The organic component is usually the pigment contained in the paint which gives it its color. The binder holds the substances together and to the wall. A solvent is added to paint to give its liquid form so that it can be spread upon the surface to be painted. This solvent evaporates in air and allows the paint to convert to the solid that we commonly see.

Paint is a form of trace evidence that may come into a forensic science laboratory from hit and run accidents, vehicles involved in automobile accidents, or on the tools used during a burglary. Paint evidence can most often be used to associate a particular suspect with a crime scene. This form of class evidence, while not enough to convict a suspect all by itself, can be an integral part of the evidence presented in a court case to convince a jury that the suspect is guilty beyond a reasonable doubt.

To make the paint chips, I borrowed 5 colors of tempera paint and some brushes from the school art department. Any type of paint would probably work. After that it was easy; directions will be in the download specified below.

The scenario: A teacher from River Hill High School walks to the parking lot after school to find that their brand new BMW Z3 convertible has been hit while they were in school. The security officer, Mr. Gonzalez, saw an older model brown sedan driving erratically through the parking lot but was unable to get the license plate number. The police examine the BMW, photograph it from every angle and take paint samples from the scrape on the side. A check of parking permits issued by the school shows that 5 students drive a brown sedan. Police take samples from each of their cars for comparison purposes.

This article features case background for students, data sheets, content links for teachers, and instructions on making your own paint chips. Unfortunately, it is too long to print here. However, a complete copy is available at articles.

Believe me, it’s so much fun you can’t have just one!

Materials List:

This lab activity will take about 50 minutes to complete with students working in groups of two students.

• modeling clay or playdoh to hold paint chips on their edge for viewing

• dissecting microscope or hand lens to view edges of paint chips; a magnification of 20-30 is recommended

• 5 different teacher created paint chips

• colored pencils for sketching paint chips

• reproducible student lab sheet

Teacher Preparation and Information:

Teacher or student background reading can be found at:





This lab activity will require some work ahead of time on the teacher’s part the first time that the activity is completed. Once the chips are made, they can be reused.

To make the paint chips, I borrowed 5 colors of tempra paint and some brushes from the school art department. Any type of paint would probably work.

1. Tape a piece of saran wrap down on the lab table. Apply the first layer of paint to the saran wrap in approximately a 20 cm by 20 cm square. This should allow you to have plenty of samples of paint chips for student use. [I chose a brown color as the first and last layer for all of my paint chips because it was dark and wouldn’t allow the other colors to show through and make it easy for students to identify the paint chips]. Allow this layer to dry.

2. Choose another color of paint. Paint a thin layer of paint over the brown paint that has dried. Allow this layer to dry.

3. Keep adding 3 or 4 different color paint layers, allowing the chips to dry in between colors. Finish with a brown layer so that your chips all look the same to the unaided eye.

4. Repeat steps 1-3 using a different color order of paint layers to create unique chips for each suspect. In my example, I have 5 student suspects.

5. Once the last layer is dry, peel off the saran wrap from each large piece. Cut the large piece into small paint chips about 1 cm by 1 cm in diameter that students will use as their suspect samples.

6. Because the suspect paint chips are small, I mark them with white dots to keep students from putting them back in the wrong container. Suspect A has one dot, Suspect B has two dots, Suspect C has three dots, Suspect D has four dots and Suspect E has five dots. (see photograph example) I store the chips in labeled film canisters to save space.

7. Fill an evidence envelope with random unmarked paint chips to have students try to determine which suspect’s car paint sample is consistent with the paint scene in their evidence envelope. Don’t forget to make a key for yourself! Here are the unknowns that I set up:

Key to Crime Scene Paint Chip Envelopes:

| |Suspect that it is | |Suspect that it is |

|Envelope # |consistent with: |Evidence #: |consistent with: |

|C.S. 1 |B |C.S. 9 |B |

|C.S. 2 |C |C.S. 10 |E |

|C.S. 3 |C |C.S. 11 |B |

|C.S. 4 |E |C.S. 12 |E |

|C.S. 5 |B |C.S. 13 |A |

|C.S. 6 |A |C.S. 14 |A |

|C.S. 7 |A |C.S. 15 |D |

|C.S. 8 |D |C.S. 16 |D |

* To keep it interesting you might create a 6th suspect sample and fill some of the crime scene envelopes with samples from this unknown car.

Hit and Run Paint Chips (Student page) Name ________________________

A teacher from River Hill High School walks to the parking lot after school to find that their brand new BMW Z3 convertible has been hit while they were in school. The security officer, Mr. Gonzalez, saw an older model brown sedan driving erratically through the parking lot but was unable to get the license plate number. The police examine the BMW, photograph it from every angle and take paint samples from the scrape on the side. A check of parking permits issued by the school shows that 5 students drive a brown sedan. Police take samples from each of their cars for comparison purposes.

Procedure:

1. Place the paint sample from student A’s car into a piece of clay so that the chip is on its’ thin edge can be seen when looking through the objective. Place the sample under the microscope.

2. Record the order of the paint layers colors that you see using words in your data table under Student A.

3. Count and record the number of layers that you see in the sample as you look from edge to edge.

4. Sketch the paint chip layers in order using colored pencils in your data table.

5. Remove this sample and put it in the proper container.

6. Repeat steps 1- 5 with the remaining student suspects paint samples.

7. When you’ve observed all of the student samples, get an unknown crime scene sample from your instructor. Be sure to note the evidence identifier (crime scene number) in your data table.

Data:

| | | | | | |Crime Scene #_____ |

|Suspects ( |Student A |Student B |Student C |Student D |Student E | |

| | | | | | | |

|Color Layer Sequence | | | | | | |

|(in words) | | | | | | |

| | | | | | | |

|Number of Layers in | | | | | | |

|Paint Chip | | | | | | |

| | | | | | | |

| | | | | | | |

|Sketch of Sample | | | | | | |

| | | | | | | |

|Colors Found in This | | | | | | |

|Sample? | | | | | | |

Conclusion:

1. From your experimental results, which suspect’s paint sample was consistent with the paint chips found at the scene of the hit and run accident? Be sure to include evidence identifier (crime scene number) in your answer!

2. Does the evidence from this experiment positively prove that this student hit the teacher’s car? What argument might a good defense attorney use in court? Explain your answer.

3. Would you be able to complete this comparison if there was only one coat color on the car? What additional testing, if any, should be done? Explain your answer.

Hit and Run Paint Chips (Teacher Resource Page)

A teacher from River Hill High School walks to the parking lot after school to find that their brand new BMW Z3 convertible has been hit while they were in school. The security officer, Mr. Gonzalez, saw an older model brown sedan driving erratically through the parking lot but was unable to get the license plate number. The police examine the BMW, photograph it from every angle and take paint samples from the scrape on the side. A check of parking permits issued by the school shows that 5 students drive a brown sedan. Police take samples from each of their cars for comparison purposes.

Procedure:

1. Place the paint sample from student A’s car into a piece of clay so that the chip is on its’ thin edge can be seen when looking through the objective. Place the sample under the microscope.

2. Record the order of the paint layers colors that you see using words in your data table under Student A.

3. Count and record the number of layers that you see in the sample as you look from edge to edge.

4. Sketch the paint chip layers in order using colored pencils in your data table.

5. Remove this sample and put it in the proper container.

6. Repeat steps 1- 5 with the remaining student suspects paint samples.

7. When you’ve observed all of the student samples, get an unknown crime scene sample from your instructor. Be sure to note the evidence identifier (crime scene number) in your data table.

Data:

| | | | | | |Crime Scene #_____ |

|Suspects ( |Student A |Student B |Student C |Student D |Student E | |

| | | | | | | |

|Color Layer Sequence | | | | | | |

|(in words) | | | | | | |

| | | | | | | |

|Number of Layers in | | | | | | |

|Paint Chip | | | | | | |

| | | | | | | |

| | | | | | | |

|Sketch of Sample | | | | | | |

| | | | | | | |

|Colors Found in This | | | | | | |

|Sample? | | | | | | |

Answers:

1. From your experimental results, which suspect’s paint sample was consistent with the paint chips found at the scene of the hit and run accident? Be sure to include evidence identifier (crime scene number) in your answer!

The correct answer depends on which crime scene sample was given to the group. I used the following key to fill my envelopes:

| |Suspect that it is | |Suspect that it is |

|Envelope # |consistent with: |Evidence #: |consistent with: |

|C.S. 1 |B |C.S. 9 |B |

|C.S. 2 |C |C.S. 10 |E |

|C.S. 3 |C |C.S. 11 |B |

|C.S. 4 |E |C.S. 12 |E |

|C.S. 5 |B |C.S. 13 |A |

|C.S. 6 |A |C.S. 14 |A |

|C.S. 7 |A |C.S. 15 |D |

|C.S. 8 |D |C.S. 16 |D |

2. Does the evidence from this experiment positively prove that this student hit the teacher’s car? Explain your answer.

No. It proves that this car may have been involved in the accident. The frequency of these layer colors and order would need to be calculated to determine how common or uncommon they are. There is also no way of knowing who was actually driving the car.

3. Would you be able to complete this comparison if there was only one coat color on the car? Explain your answer.

If there was only one color on the car, this technique would not be effective. All of the samples would appear microscopically similar. A chemical analysis may prove more useful.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download