Crystal violet is the name given to a group of similar organic compounds used as pH indicators and dyes. Other names it goes by are:

  • Methyl Violet
  • Gentian Violet (term typically used in Europe)
  • Gentian Crystal Violet
  • Basic Violet #3
  • CI 42555 or C.I. 42555


Methyl violets are mixtures of tetramethyl, pentamethyl and hexamethyl pararosanilins. By blending the different versions, dyemakers can create different shades of violet in the final dye. The more methylated the compound (i. e., the more methyl groups attached), the deeper blue the final color will be:

Tetramethyl (four methyls) is known as methyl violet 2B. Solid samples appear blue-green in color; melting is at 137 °C (279 °F). It is used as a pH indicator, with a range between 0 and 1.6. The protonated form (found in acidic conditions) is yellow, turning blue-violet above pH levels of 1.6. = 1.6)
Pentamethyl (five methyls) is known as methyl violet 6B, and is darker blue (in dye form) than 2B.

Hexamethyl (six methyls) is known as methyl violet 10B, or specifically as crystal violet or Gentian violet. This is much darker than 2B, and often darker than 6B. Methyl violet 10B is the active ingredient in a Gram stain. In the Gram staining method, crystal violet is used to differentiate between Gram Positive and Gram Negative bacteria.


Crystal violet or methyl violet is used in many applications, including:

  • As a pH indicator (yellow to violet with the transition at a pH = 1.6)
  • In the medical community, it is the active ingredient in Gram’s Stain, used to classify bacteria
  • The dye destroys cells and is used as a moderate-strength external disinfectant
  • It is widely used as a purple dye for textiles such as cotton and silk
  • It provides a various deep violet colors for paints and printing ink
  • It is used to dye paper

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