Abstract: A freeze and thaw indicator is provided utilizing the expansion characteristics of water when it undergoes a change from the liquid state to the solid state. An ampul having one side made weaker than its opposite side is substantially filled with water. Indicator paper having ink printed on one side is situated adjacent to the ampul. The indicator paper and ampul are housed in a blister pack plastic container for protecting the ampul from breakage. When the temperature around the indicator reaches the freezing point of water, the ampul breaks. During a subsequent thawing, the water flows on to the indicator paper causing the ink which is printed on one side to wick up, thereby indicating that the freeze or thaw has taken place.

Abstract: An indicator device for use as a time indicator or a time-temperature indicator. A container is provided for housing a frangible capsule and a porous carrier. A vapor generating chemical is enclosed in the capsule. A mixture, including a second chemical, a pH change responsive indicator, and a gel forming agent are impregnated in the porous carrier. The pH of the vapor is different from the second chemical. A gel is formed from the mixture and provides uniform dispersion of the second chemical and the indicator throughout the porous carrier, as well as provides an impedance to the vapor as it moves through the porous carrier. The device is thus useful as an elapsed time indicator for certain temperature ranges as well as a time-temperature indicator for wider temperature ranges.