Litmus Paper from Dye Lichen

Litmus is a blue dye from lichens that turns red in acid and back to blue in alkali. The lichen is ground with sodium carbonate and ammonia and stirred for about four weeks while it turns from red through purple to blue; alcohol then takes out the red orcein. Unsized paper soaked in the blue litmus and dried is litmus paper. The picture: strips of litmus paper, blue at one end and turned red at the other.