Science, Tech, Math › Science Litmus Paper Definition Chemistry Glossary Definition of Litmus Paper Share Flipboard Email Print Litmus paper is a type of pH paper made from lichen pigments. Meganbeckett27/Wikimedia Commons/CC-BY SA 3.0 Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated June 06, 2019 Litmus paper is filter paper which has been treated with a natural water-soluble dye obtained from lichens. The resulting piece of paper, called "litmus paper", can be used as a pH indicator. Blue litmus paper turns red under acidic conditions (pH below 4.5) while red litmus paper turns blue under alkaline conditions (pH above 8.3). Blue litmus does not change color under alkakine conditions, while red litmus paper does not change color under acidic conditions. Neutral litmus paper is purplish in color. Neutral litmus paper turns red under acidic conditions and blue under alkaline conditions. While litmus paper may be used to determine whether an aqueous solution is an acid or a base, it not good for estimating the pH value of the liquid. History and Composition Spanish physician Arnaldus de Villa Nova first used litmus paper around 1300 AD. Originally, litmus was a blue dye obtained from any of a number of lichen species found in the Netherlands. Today, litmus is prepared mainly from the species Roccella montagnei from Mozambique and Dedographa leucophoea from California. However, litmus may contain from 10 to 15 different dyes. How Litmus Paper Works Red litmus contains a weak diprotic acid. Upon exposure to a base, hydrogen ions from the acid react with the base, producing a color change to blue. Blue litmus paper, on the other hand, already contains the blue conjugate base. It reacts with an acid to change to red.