I am testing electronics with many potentially unstable contacts, and I wish to monitor if they rise above 50 to 90 degrees Celsius, i.e. using carbon paper that would darken progressively from 50 to 90.
The substance should stay a specific warning color if it goes too high and not change hues again same as thermochromic pigment, so that I can detect high temps.
I hope you know a chemistry trick that could help? Thank you.