"Acids and bases can be detected by a group of chemical compounds called acid-base indicators. One of the first known naturally occurring indicators was a type of lichen called litmus. (Lichens are plant-like growths that are often found on rocks and tree bark.) Litmus turns red in the presence of an acid or blue with a base. Today's experiment is to create a homemade version of that Litmus test." She tapped on the chalkboard with his piece of chalk and said, "I've created a list of things you'll need to pull from the cupboard. Take your time and don't be afraid to ask questions."