Litmus paper is an unsized paper treated with litmus for the use as an acid-base indicator, in an acid it turns red, and in a base it turns blue.
Generalic, Eni. "Litmus paper." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
Glossary
Periodic Table