[William Finucane] is making his own litmus paper by harnessing the power of cabbage. The process is much easier than the faux gunpowder he made, as it take just the one ingredient and a few kitchen tools.
In case you’ve forgotten your High School chemistry, Litmus is a set of dyes that change color when exposed to basic or acidic materials. It is common in liquid form, or as a paper. [William] is getting his dye from the leaves of red cabbage by running half a head through a blender with just a bit of water. Once that is reduced to pulp and boiled in the microwave (mmm, must smell great!) he separates the liquid using a coffee filter. A fresh coffee filter serves as a donor for the substrate, just dip some strips in the cabbage juice and let them dry. You can test them with some Ammonia as seen in the video after the break, or just start grabbing whatever is under the sink and see what happens.