A natural, blue dye extracted from certain lichens, such as Roccella tinctorum or Lecanora tartarea. Litmus is water soluble and may have been occasionally used as a watercolor pigment, textile dye, or wood stain. In alkaline solutions (above pH 8.3) litmus turns blue and in acid solutions (below pH 4.5) it is red. The neutral tint is violet. Litmus is a widely used acid-base indicator, either in solution or on dyed paper strips. Other natural dyes, archil, logwood, turmeric, and turnsole, are also acid-base indicators.
Synonyms and Related Terms
lichen blue; lakemus; Roccella tinctorum; Lecanora tartarea
Soluble in water.
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