Saturated salt solutions
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Description
In a closed environment, saturated salt solutions can maintain an equilibrium with the moisture in the air. At low humidity, fully hydrated (liquid) salts can volatilize water. The solid salts can absorb moisture when the humidity is high. Saturated salt solutions are a low maintenance method to provide a constant humidity level within a display case (Eggert 2022). Unlike silica gel, which requires reconditioning, the saturated salt solutions only need supplemental distilled water added once a year.
Relative Humidity % at Selected Temperatures
| Saturated Salt Solution | Chemical Formula | 68°F | 77°F | 86°F |
| Lithium chloride | LiCl H2O | 12. 4% | 12. 0% | 11.8% |
| Potassium acetate | CH3CO2K | 23. 3% | 22. 7% | 22.0% |
| Magnesium chloride | MgCl2 6H2O | 33. 6% | 33. 2% | 32.8% |
| Potassium carbonate | K2CO3 2H2O | 44. 0% | 43. 8% | 43.5% |
| Potassium nitrate | KNO3 | 49. 0% | 48. 1% | 47.2% |
| Magnesium nitrate | Mg(NO3)2 6H20 | 54. 9% | 53. 4% | 52.0% |
| Sodium nitrate | NaNO3 | 65. 3% | 64. 3% | 63.3% |
| Sodium chloride | NaCl | 75. 5% | 75. 8% | 75.6% |
| Ammonium sulfate | (NH4)2SO4 | 80. 6% | 80. 3% | 80.0% |
| Potassium nitrate | KNO3 | 93. 2% | 92. 0% | 90.7% |
| Potassium sulfate | K2SO4 | 97. 2% | 96. 9% | 96.6% |
Table obtained from Technical Bulletin No. 5, Creating and Maintaining Humidities by Salt Solutions. Hygrodynamics, Inc.
Synonyms and Related Terms
salt solutions
Collection Risks
- Magnesium chloride can release chlorine
Resources and Citations
- G. Eggert, "Saturated salt solutions in showcases: humidity control and pollutant absorption", Herit Sci 10, 54 (2022). https://doi.org/10.1186/s40494-022-00689-3
- AIC Conservation Wiki: Exhibit Technical Notes: Environmental Control
- Exhibit Guidelines Technical Note: Conditioning Silica Gel with a Saturated Salt Solution
- L. Greenspan "Humidity Fixed Points of Binary Saturated Aqueous Solutions" J. Research of the NBS, Vol 81A, No. 1 1977.
- Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
- Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002