Dual heat-freeze indicator

A combined low temperature and high temperature historical temperature exposure indicator, comprising:

• a substrate;
• a low temperature indicator material supported by the substrate and provided in a first initial color state;
• a high temperature indicator material supported by the substrate and provided in a second initial color state;
• and
• a dark background provided on the substrate behind both the low temperature indicator material and the high temperature indicator material;
• wherein at least a portion of the low temperature indicator material overlays at least a portion of the high temperature indicator material;
• wherein the low temperature indicator material is configured to change from the first initial color state to a first exposed color state responsive to the indicator being exposed to a temperature below a low temperature threshold, the low temperature indicator material configured to return from the exposed color state to the initial color state responsive to the low temperature indicator material being subsequently exposed to a temperature above a reset temperature threshold;
• wherein the high temperature indicator material is configured to irreversibly change from the second initial color state to a second exposed color state responsive to the indicator being exposed to a temperature above a high temperature threshold, where the high temperature threshold is lower than the reset temperature threshold;
• wherein the low temperature indicator material is transparent in the first initial color state and dark colored and opaque in the first exposed color state, and wherein the high temperature indicator material is light colored and opaque in the second initial color state and transparent in the second exposed color state, revealing the dark background when both the high temperature indicator material and the low temperature indicator material are transparent, the combined indicator appearing dark after being exposed to either a low temperature excursion below the low temperature threshold or a high temperature excursion above the high temperature threshold.

A method of creating a combined low temperature and high temperature historical temperature exposure indicator, the method comprising:

• receiving a substrate;
• receiving a low temperature indicator material configured to transition from a high temperature color state to a low temperature color state responsive to the indicator being exposed to a temperature below a low temperature threshold, the low temperature indicator material configured to return from the low temperature color state to the high temperature color state responsive to the low temperature indicator material being subsequently exposed to a temperature above a reset temperature threshold;
• receiving a high temperature indicator material in an initial color state, the high temperature indicator material configured to irreversibly change from the initial color state to an exposed color state responsive to the indicator being exposed to the temperature above a high temperature threshold, where the high temperature threshold is lower than the reset temperature threshold;
• forming a heterogenous mixture of the low temperature indicator material and the high temperature indicator material;
• applying the heterogenous mixture to the substrate;
• and
• maintaining the combined low temperature and high temperature indicator materials at a temperature above the low temperature threshold and below the high temperature threshold.