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Secret Message

Experiment #10 from Forensic Chemistry Experiments

Education Level
High School


Your lab has been asked to help the prosecution explain the note that was discovered and introduced into evidence. How does it work? Why is a special light required to read the message?

For some chemicals, when light of one wavelength (color) is shined on them, they will absorb some of the energy and become excited as they reach a higher level of energy. These higher energy levels are frequently unstable, so the chemical will re-emit some light at a different wavelength to return to a lower energy state. This process is called fluorescence.


  • Conduct an investigation to capture absorbance and fluorescence spectra of invisible inks in solution.
  • Analyze the spectra to identify the wavelengths of maximum absorbance and fluorescence for each ink.
  • Use mathematical representations to calculate the frequency and energy of the photons producing the peaks in the spectra.
  • Interpret data to explain the difference in energy of the photons producing the spectra for each ink.

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

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This experiment is #10 of Forensic Chemistry Experiments. The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.

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