Humidity indicator cards do not have a fixed "shelf life," but their performance deteriorates with storage conditions and usage, leading to insensitive or irreversible color changes. Determining whether a card is "invalid" or "unusable" requires a comprehensive evaluation of its appearance, color reaction, storage method, and usage records.
Observe the color: Does it maintain its initial dry color?
A normally unused humidity indicator card should be a uniform blue (or brown, depending on the model).
If the card shows localized pink or mottled discoloration even when unopened or stored in a sealed container, it indicates a failed seal or prolonged exposure to moisture, potentially rendering it inaccurate.
Special Note: Some cobalt-free humidity cards are initially brown or light brown, turning yellow after becoming damp. Refer to the instruction manual for confirmation.
Normal State: Indicator points are clear, colors are consistent, and there is no contamination.
Abnormal Signals: Premature color change, blurred color, water stains or dirt.
Test Color Change Response: Can it properly sense humidity changes?
A simple test can be performed to verify the function:
Take a suspected faulty card and place it in a humid environment (such as a sealed box with a damp towel) for 10-15 minutes;
Observe whether the corresponding humidity point changes from blue to pink (or brown to yellow);
Then place it in a dry environment (such as a sealed container with fresh desiccant) and observe whether it gradually returns to its original color within 24 hours.
Effective Standard: Noticeable color change and reversible recovery
Failure Symptoms: No reaction, slow color change, irreversible damage
Check Storage Conditions and Usage Frequency
According to reference materials, the following conditions can affect the lifespan:
Excessive Exposure Time: Each use exceeding 30 seconds of exposure to air can easily lead to moisture absorption and failure.
Repeated Opening of Packaging Can: Opening the can more than 3 times without replacing the internal desiccant increases humidity, affecting card quality.
Reusing Without Drying: Reusing discolored cards without baking at 100℃ for 5-6 minutes may result in residual moisture affecting accuracy.
Improper Storage: Direct sunlight and high temperature/humidity environments will accelerate material aging.
Recommendation: Humidity cards that have not been used for a long time should be dried before use to activate their performance.