Unlike thermochromic inks, these inks, invisible after printing, become irreversibly colored when subjected to high temperatures. 2 temperatures are available:
A first group will react at a temperature of 75°C. Once heated beyond this temperature the color change to black or red will be irreversible.
A second group will react at 95°C and will also show a color change to Blue, Black, Red or Green but in this case the coloring will not be completely irreversible and the ink becomes transparent again after a certain period of time. These inks are not completely transparent but rather milky.
