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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

Physical and Chemical Properties

Soluble in water.

Resources and Citations

  • R. J. Gettens, G.L. Stout, Painting Materials, A Short Encyclopaedia, Dover Publications, New York, 1966
  • Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
  • S.R.Trotman, E.R. Trotman, Textile Analysis, J.B. Lippincott Company, Philadelphia, 1932
  • R.D. Harley, Artists' Pigments c. 1600-1835, Butterworth Scientific, London, 1982
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 5574
  • Book and Paper Group, Paper Conservation Catalog, AIC, 1984, 1989

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