Carnegie Mellon University

The Jewelry Store Robbery: Procedure

Read all directions completely before beginning the tests. Wear safety glasses during flame tests.

Microscopic Examination

  1. Using forceps carefully remove a fiber sample from one of the sample bags and place it on a clean microscope slide. drop of water on the sample and cover it with a cover slip. This type of sample preparation is known as a "wet mount". Place the slide in position on the microscope stage slide holder.
  2. jewelry-robbery1

  3. Examine the fiber sample using a magnification of 75X or 150X. Adjust the mirror (or light) so that the sample is illuminated. Note any unusual characteristics on your data sheet.     For example, does the fiber appear to be tightly or loosely braided? Are the fibers smooth or rough looking? Are the strands orderly arranged or very disorganized? Do they have a shiny or dull appearance?


Flame Test

  1. Place a candle in a holder that will not be knocked over easily. A broad-based candle works well.  Carefully light the candle. Using forceps, remove a fiber sample from one of the sample bags.
  2. Still using the forceps carefully move the fiber close to the flame. Observe what happens.  Does the fiber melt curl away from the heat, burst into flames, etc.?
  3. Now put the fiber into the flame. Does it burn rapidly, slowly, or melt?  Does it self-extinguish when removed from the flame or continue to burn?  Blow out the burning fiber if necessary. Do not allow it to burn all the way to the forceps.
  4. Observe the burned end of the fiber.  Did the fiber melt?  Did ash form?  What color is the ash?

Record all of your observations on your data sheet.

Test the fiber sample from the crime scene and those recovered from the employees and compare the results.  Does your data reveal who may be the thief?

See a template data sheet [.pdf] or a sample data sheet [.pdf].


Discard used fiber samples.  Make sure that the candle is completely extinguished and that the wax has cooled and hardened.  Clean and dry the microscope slides and cover slips and return them to their containers.

Store microscope (and light) as directed by your teacher.