Summary

In this lesson students will explore photodegradation of color. First, students will view how fading of paint has affected Van Gogh’s great works of art and the efforts that are being taken to conserve these works. While exploring, students will actively engage in research to relate the fading process to redox reactions, X-Ray diffraction, solute-solvent interactions, and light/energy calculations. Students will then act as an Engineering Task Force and brainstorm to identify how photodegradation affects modern day objects and plan how to address their fading in an effort to market to the airliner Jetstar.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
• HS-PS1-7: Use mathematical representation to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
• HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
• HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
• HS-ETS1-2: Design a solution to a complex real-world problem by breaking it down into small, more manageable problems that can be solved through engineering.
• HS-ETS1-3: Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to

• Use examples from history to identify the main reasons for the degradation of color in paints.
• Predict the charges of atoms before and after a redox reaction.
• Calculate the amount of energy found in portions of the visible light spectrum.
• Hypothesize what components in paint resist the photolytic effect of ultraviolet radiation.

Chemistry Topics

This lesson supports students’ understanding of

• Energy
• Electromagnetic Radiation
• Redox Reactions
• Oxidation Number
• Oxidation
• Reduction
• Bonding
• Molecular Structure
• Intermolecular Forces

Time

Teacher Preparation: 15–20 minutes

Lesson:

• Engage: 10minutes
• Explore: 10 minutes
• Explain: 45 minutes
• Elaborate: 20 minutes
• Evaluate: 60 minutes (+ 2 week wait period)

Materials

• Copies or access to “Van Gogh’s Fading Colors Inspire Scientific Inquiry” from ACS Publication: Chemistry & Engineering News, Volume 94, Issue 5, February 2016
• Internet access

Safety

• No specific safety precautions need to be observed for this activity.
• If teacher chooses to perform a demonstration during the Explore section, follow the safety guidelines specific to the demonstration.

Teacher Notes

• Engage:Start by using a Think-Pair-Share Activity. Display the image “Time Machine” from page 6 of the C&EN article. The image compares the faded original van Gogh painting “The Bedroom” to a digitally restored version. The left picture is the faded version of the original work of art. The image on the right is the digital reproduction as it probably looked when first painted. The fading in the left picture is caused by degrading of the red pigments used in Van Gogh’s original painting. Possible observations will be:
  • Different red of the bed cover
  • Purple versus blue door and walls
  • The light splotch under the chair that only appears in the left picture
  • Richness of color in the floor in the right picture

• Think: Ask students to individually think of answers to the following:
  • WHY do colors fade?
  • Do some fade faster than others?
  • What environmental conditions influence pigments in paint to fade?
  • What can be done to prevent colors from fading?

• Pair: Students will share their answers with their lab group or person sitting next to them.
• Share: Each group will be asked to share their ideas with the rest of the class.

• Explore: Show students this SciShow video, “Photodegradation: Why Your Prints Fade When Left in Sunlight.” It is 2 minutes and 16 seconds in length.
• Ask students to answer the following questions again:
  • Why do colors fade?
  • Do some colors fade faster than others?
  • Students should deduce red and orange pigments absorb higher frequencies of light. These higher frequencies relate to more energy absorbed to fuel reactions that lead to degradation. The degradation may or may not be of the pigment itself. The binders and additives in the paint may be what are altered leading to flaking or discoloration.

• Discuss with students the role light plays in this process, but reiterate that other environmental factors can contribute to the fading process.
• The teacher may choose to perform or show a video of a demonstration allowing students to visualize the difference in color observed in metals of different oxidation states: Cr⁺⁶ to Cr⁺³, Fe⁺² to Fe⁺³, Cu⁺ to Cu⁺², Pb²⁺ to Pb⁴⁺, etc. There are also a variety of video clips online to facilitate this viewing without the use of the more dangerous metals. A good example is the reaction that occurs during a Breathalyzer test.

• Students are to read “Van Gogh’s Fading Colors Inspire Scientific Inquiry” from ACS Publication: Chemistry & Engineering News, Volume 94, Issue 5, February 2016. In their lab groups, students are to answer the questions on the student handout “Pay Attention! This will be Faded!” The handout addresses questions generated from the reading, but also requires the student to perform a bit of research to develop a clear understanding of the concepts.

• Explain: Discuss the findings with the students. Clarify any misconceptions generated while reading the article and address the energy calculation. An answer key has been provided for teacher reference.
• Elaborate: Bring the discussion to modern day paints and surfaces affected by the fading of the paints. Be sure to address the light source of the fading as UV radiation. Ask students to brainstorm techniques companies may take to discourage the fading of paint. Some of these include:
  • Using binders that do not absorb ultraviolet light
  • Using a reflective topcoat
  • Including additives with UV absorbers, drawing the energy from the binder
  • Using a pigment that is absorptive that protects the vehicle
  • Using luminescent pigments which absorb energetic waves and re-emit longer, lower energy waves of light
  • Using UV absorbers similar to sunscreens that absorb high energy UV light and convert it to heat energy; stable form not degraded by UV light.
• Working in groups, students will develop a proposal for the business of Jetstar. The students are to design a proposal focusing on a product that will address fading issues of the paints. Use the “Don’t let Jetstar Fade Away” student sheet. The groups will be guided to make a marketing tool used to sell a self-designed product to Jetstar. This PPG branding suite resource may be helpful for student reference.
• Evaluate: The rubric outlines the key elements in the proposal and requires students to make an advertising implement. A brochure, prezi, or webpage are simply ideas—allow students the flexibility to choose the platform