A simple and inexpensive invisible ink system based on red cabbage extracts

Lauren Keiller, Iain L. J. Patterson, Dominic Stewart, Iain Smellie*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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The use of red cabbage (Brassica oleracea var. capitata F. rubra) extract as a pH indicator is a versatile and popular demonstration that is employed by educators in many schools and universities. Previous variations of this demonstration have used red cabbage extracts to prepare paper that changes color when solutions of acid or base are applied as “inks”. In this report, we highlight the ability of red cabbage extracts to function as invisible inks. Colorless solutions are prepared by bleaching anthocyanin extracts with aqueous sodium metabisulfite, and the resulting mixture can then be used to write hidden messages on paper. The invisible messages can be revealed by the addition of citric acid solution, or by using potassium aluminum sulfate (alum) as developers. The demonstration does not require specialist equipment or chemicals, and options to use additional plant sources to prepare the ink are described.
Original languageEnglish
Pages (from-to)1398-1403
Number of pages6
JournalJournal of Chemical Education
Issue number3
Early online date28 Feb 2023
Publication statusPublished - 14 Mar 2023


  • High school/introductory chemistry
  • First-year undergraduate/general
  • Demonstrations
  • Acid/bases
  • Aqueous solution chemistry
  • Plant


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