This investigative case module was prepared as part of a BioQUEST faculty development workshop entitled Selected Cases at Beloit College in June 1999. The cases, resources, and implementation strategies were developed by participants for use with their own students. We invite you to adopt and adapt the following materials.

The BioQUEST Curriculum Consortium is committed to the reform of undergraduate biology instruction through an emphasis on engaging students in realistic scientific practices. This approach is sometimes characterized as an inquiry driven approach and is captured in BioQUEST's three P's (problem-posing, problem-solving, and peer-persuasion). As part of this workshop groups of faculty were encouraged to initiate innovative curricular projects. We are sharing these works in progress in the hope that they will stimulate further exploration, collaboration and development. Please see the following links for additional information:

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The Case: Faded Memories ...

Caroline was very excited that she would get to visit her brother over spring break. Her brother, Mark, recently accepted a job in San Diego and she hasn't seen him in almost 7 months. On her trip out West, Caroline stopped in rural Nebraska to visit her great Uncle Alvin.

Uncle Alvin lives on a huge soybean farm, much unlike Caroline's tiny apartment in the middle of the city. Uncle Alvin is no longer working the fields, but he loves sharing stories of the hard work that built the farm. She enjoyed his stories of life on the farm and his descriptions of technological advances he's seen in his lifetime.

Caroline showed Uncle Alvin her new laptop and dialed up to get a slow, but usable internet connection. While Caroline was frustrated by how long it took to call up her college homepage, Uncle Alvin was amazed. Caroline logged in and sent an instant message to her brother Mark. Uncle Alvin could not believe that they were conversing with his nephew all the way in California. He was most delighted by Mark's personal web page that had photos of his new friends at the beach in San Diego.

Uncle Alvin said times have really changed and he recalled the days when a photographer would go from town to town taking family photos. He wanted to show Caroline pictures from his childhood. The two climbed upstairs to a dusty attic and found an old shoebox full of letters, photos and postcards.


Caroline found a black and white family portrait that had faded. The image was so faint you could not even see the face of the baby in the photo. Uncle Alvin was terribly sad since it was the only photo he owned that included the entire family. Uncle Alvin was just a young boy in the photo. Other photos in the box were brown. They were not brown with age, but seemed to have been developed in a brown print. Caroline had never seen that type of photo. Last semester her general chemistry course talked about the role of light in creating photographic images. However, the class never discussed the degradation of photographs.

Caroline told Uncle Alvin not to worry, she would take the photos to a studio that digitally restores photographic images. However, she could not explain why the photos had faded and she really didn't know why some of them were brown.


Daphne Norton, Ph.D.
Georgia Perimeter College

Case Author:
Daphne Norton Emory University:Center for Science Education

Case Analysis

The students must determine how the photos faded. They will be asked to explain how the photographs were prepared and then consider why and how they faded.

The students will be asked to develop a simple experimental procedure for testing their explanation of how the images were formed.

Students will submit a list of chemicals and be given materials and access to the lab during class time to test the hypothesis.

They should consider the following questions:

What is the chemical process of photography?

How does light react with film?

What oxidation-reduction reactions take place?

How do developing solutions create the image?

How do old photos degrade?

What is the reverse chemical process?

What progress has been made in stabilizing photographic images?

Option: Include a know / need to know chart like the one below:

What do you know?
What do you need to know?
   

Learning Goals

Goal(s)

* To make a connection between chemistry and real world experiences and applications

* To understand the reduction-oxidation chemistry of photography

* To introduce the concept of photochemistry and explain the effects of light on electron transfer

* To examine the photosensitivity of silver halide salts in a laboratory exercise

* To reproduce the chemical process of photographic development in a laboratory setting

* To recognize the ongoing search for new and improved technology (i.e. more stable photographs)

Standards

Undergraduate

 

Investigations and Activities

The students must identify what chemical process is required to prepare a photograph.

They should recognize the oxidation-reduction chemistry required to generate the photographic image.


Laboratory exercise:

Prepare gelatin salting solution and silver nitrate sensitizing solution.

Expose treated paper to sunlight to create image.

Treat exposed paper with a solution of photographic fixer (sodium thiosulfate).

Discuss chemical reactions at each step.

 

Resources

Chemistry Textbooks: Chapter discussing oxidation/reduction reactions

General books on photography

http://wwwchem.csustan.edu/chem2500/labs/labintro.htm

http://cator.hsc.edu/~mollusk/ChemArt/photo/index.html

http://www.cheresources.com/photochem.shtml

http://www.digitalcentury.com/encyclo/update/photo_hd.html

http:/www.photo-phixer.com/restorations.htm

Students will usually obtain additional references or resources
to help answer or explore their questions.

Special Data Items

1. faded.JPG

 

Student Products

Each group must present a report explaining why the photographs have faded and why some are brown images and others resemble the traditional black and white photos we have today. This will be a formal written report with experimental data from the lab experiment.

Each group must prepare a procedure to test their chemical hypotheses of how the prints were made. A simple experiment with salted paper prints should be designed. The students will arrive in lab and submit their procedure. They will be graded on the feasibility of the proposed experiment including safety precautions. Basic chemicals will be provided and directions will be given when preparing solutions and following safety protocols.

Assessment and Evaluation Plan

Each group will submit their responses in two parts: written report and lab component.

Written report: An investigative explanation of the faded photographs. The report should explain the simple photography of salted paper prints. The explanation of the degradation of the photo should be given. In addition, the chemistry of salted silver prints should be supported by lab results.

Lab exercise: The students will be graded on the development of a laboratory exercise to produce a simple salted paper.

They will be graded on the final product. Were they able to generate a salted paper image? The procedure will be recorded and observations and the final product will be used to support the written report and explanation of the faded photographs.

 

Implementation

Course name:
Survey of General Chemistry
Likely sequence in syllabus:
Chemical Reactions
Time during term:
Weeks 4-5
Duration:
Two weeks to work on report and prepare lab procedure.
Setting:
Lecture with additional lab exercises
Students in course:
Non-majors
Collaborative elements:
Work in groups.
Share access to resources.
Likely to discuss cases outside of class.
Additional notes:

 

Credits

http://www.photo-phixer.com/restorations.htm

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