Humidity indicator card

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Humidity indicator cards


A chemically modified paper card used as a general indicator of relative humidity. A humidity indicator card contains several small discs of absorbent paper impregnated with varying proportions of cobalt chloride. Anhydrous cobalt chloride is blue and the hydrated salt is pink. The discs change color according to the atmospheric humidity and provide an general level of relative humidity ranging from 10 to 100 %. Temperature can affect the readings; high temperatures may cause the card to indicate a humidity lower that what is actually present.

6-spot humidity indicator card

Synonyms and Related Terms

humidity card; RH indicator card; HIC; Hydrion [University Products]; 6-spot HIC [Static Control]; SMD Humitector [Humidial Corp.]

Resources and Citations

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 206
  • Marjorie Shelley, The Care and Handling of Art Objects, The Metropolitan Museum, New York, 1987
  • Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
  • Conservation Support Systems, Catalog, 1997