Silica gel desiccant is a highly active adsorbent material, usually made by reacting sodium silicate with sulfuric acid, and after a series of post-treatment processes such as aging and acid bubbles.
The color-changing desiccant is a chemical indicator added on the basis of the silica gel desiccant, usually divided into blue indicator and orange indicator.
The blue silica gel desiccant will turn pink when it is saturated with water, mainly because the blue silica gel contains cobalt dichloride. Cobalt dichloride itself has the characteristic of changing from blue to pink due to water absorption. However, cobalt dichloride contains poison, and should avoid contact with food or inhalation. The EU listed it as a toxic substance in 2000.
The orange silica gel desiccant will become dark green when it is saturated with water, mainly because it contains methyl violet. Methyl violet will change color due to pH changes. Methyl violet will change from orange to dark green in the range of PH0.13-0.5, and the PH value will change with the water content in the desiccant, so it will have an indicating effect.
The color-changing silica gel serves as a reminder. The color-changing reminds us that these desiccants are saturated and should be replaced.