Here's what Desco says ... Humidity Indicator Card (HIC) A card on which a moisture-sensitive chemical is printed such that it will change color from blue to pink when the indicated relative humidity is exceeded. This is packed inside the moisture-sensitive bag, along with the desiccant, to aid in determining the level of moisture to which the moisture sensitive devices have been subjected.” (IPC/JEDEC J-STD-033A section 1.5.7) Application 1. The humidity indicator spots will change from blue (dry condition) to pink (humid condition) as the relative humidity changes in the volume of air surrounding the indicator. 2. Relative humidity is indicated at the lavender color. 3. Indicator spots will change within eight hours of being exposed to a change in relative humidity. 4. The humidity indicator spots are reversible, and the pink spots will change back to blue when the volume of air is dried. Humidity indicator cards with pink or lavender spots can be returned to a blue color by placing indicators in a sealed container with 33 grams (1 unit) of desiccant for four hours. 5. The highest humidity indicator spot should be blue before being put into use. 6. The humidity indicator will be at its most accurate at a temperature of 23 °C (73 °F). 7. Avoid contact with indicator spots. Wash any irritated areas with clean water. Handling 1. Store humidity indicators in original container with desiccant when possible and keep sealed. Never reuse a indicator card if it has already changed color. 2. Replace desiccant bag after three openings of container. 3. Store in dry, cool area. 4. Keep indicators out of direct sunlight. 5. Keep humidity indicators away from water or steam. 6. Ammonia gases will damage humidity indicators.
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