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The Use of Cobalt Chloride in Silica Gel

Updated on June 20, 2011

All Silica Gel absorbs moisture.  Indicating Silica Gel is impregnated with a chemical that changes color when it comes in contact with moisture.  This color change indicates when the Silica Gel is fully saturated and needs to be changed.  Cobalt Chloride has long been the favored chemical to use for Indicating Silica Gel, but research is showing that it isn't the safe choice.

Indicating Silica Gel

Silica Gel, like in the packets you find in shoe boxes and packaged with electronics, is clear and comes in beads.  The beads are solid, dry, and clear, not wet or slimy as the name Gel might suggest.  Indicating Silica Gel is Silica Gel beads that have been impregnated with a color changing additive (which is usually less than 1% of the total weight) that reacts to the moisture as it is absorbed by the Silica Gel. 

Indicating Silica Gel is used when low humidity must be maintained in a container for an extended period of time.  The color changing additive lets the consumer know when the Silica Gel is fully saturated and needs to be either replaced or reactivated.  Indicating Silica Gel is used in such situations as humidity control in museum cases or in archival boxes for important documents.

Dry Cobalt Chloride
Dry Cobalt Chloride
Fully Saturated Cobalt Chloride
Fully Saturated Cobalt Chloride

Cobalt Chloride as an Indicator

Cobalt Chloride starts out blue when it is dry.  As it begins to absorb moisture, it turns purple.  When it is fully saturated, Cobalt Chloride turns pink.  Cobalt Chloride has been used in many capacities to indicate moisture levels.  Paper can be infused with it in order to detect leaks, weather "predicting" novelty items were coated in it, and Silica Gel can be impregnated with it to indicate when the Silica Gel is fully saturated. 

Health and Safety Concerns with Cobalt Chloride

Companies who use cobalt chloride have released Material Safety and Data Sheets (MSDS) that describe cobalt chloride as a skin and respiratory irritant. MSDS reports on the carcinogenic properties of cobalt chloride vary, some state that there is no risk while others say that it has caused cancer in laboratory animals. The warning label that comes with cobalt chloride is that any exposure can irritate the lungs and skin and long term exposure can affect the heart, kidneys, lungs, and thyroid. Protective eyewear, gloves, respirators, and ventilation hoods are the recommended protection measures for handling cobalt chloride.

Companies that use cobalt chloride as the indicator in their Indicating Silica Gel are putting their employees and consumers, as well as the environment, at unnecessary risk. British regulations have required that cobalt chloride be handled and disposed of as a hazardous material since 2001. Cobalt chloride, if not properly disposed of, can leach into the ground and and water supply, contaminating both. Although the UK has taken steps to protect against the possibly carcinogenic properties of cobalt chloride, similar measures have not been taken in the United States.

Fresh Orange to Green Indicating Silica Gel
Fresh Orange to Green Indicating Silica Gel
Saturated Orange to Green Indicating Silica Gel
Saturated Orange to Green Indicating Silica Gel

There is a Safer Option

Responsible companies have stopped using cobalt chloride in their Indicating Silica Gel. Instead of the traditional blue to pink Indicating Silica Gel, these companies have started using a reformulated indicator that changes from orange to green. By doing so, these companies have not only produced a product that is safer for their consumers and the environment, but have also created a safer work environment for their employees.

Indicating Silica Gel Can be Used with Dry Boxes


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    • Andi Dulude profile image

      Andi Dulude 8 years ago

      It is a reaction that occurs in the cobalt chloride when it comes in contact with the cobalt chloride.

    • profile image

      yuvaraj 8 years ago

      how cobalt chloride change its color