Mimicking Stained Glass: A Hands-On Activity for the Preparation and Characterization of Silica Films Colored with Noble Metal Ions and Nanoparticles

We here propose a simple and fast hands-on activity requiring limited equipment, to introduce students of various levels (bachelor's or high school) and backgrounds (from science to arts) to the chemistry of color. The different colors of stained glass are replicated through the deposition, on ordinary glass slides, of silica coatings colored by addition of metal ions and nanoparticles. A silica sol is used as a matrix to embed metal ions, followed by an in situ reduction activated by thermal treatment on a hot plate. The formation of metal nanoparticles by this procedure induces plasmonic colors in the glass coating, thus "mimicking" the ancient procedure of stained-glass fabrication through a simple and quick method. Characterization of the colored glass by optical spectroscopy is also presented. This easily reproducible activity demonstrates basic concepts of redox reactions, chemistry of color, and plasmonic nanoparticles. Thanks to its interdisciplinary character and immediate and tangible results, this activity is well-suited for teaching laboratories for bachelor's and high school students as well as for public engagement activities.