I love this idea because it not only makes use of what would otherwise be trash, but also because kids will think it is way cool. You could even tie in some science by observing, predicting and discussing colors.
Team up with colleagues and get the word out that you are in search of old, dried-up markers. I'm not a fan of glass in the classroom. I would use Crystal Lite Containers because they are not breakable and would allow the marker to stand without falling over. Also, they are somewhat transparent and would allow the kids to (sort of) see the colors change from the outside.
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