Thermochromic pigments change colour at a set temperature and change back when they cool. They make "drink is cold" labels, touch-reveal packaging and heat warnings possible.
How they work
Most reversible thermochromics are microcapsules containing a leuco dye, a colour developer and a solvent with a defined melting point. Below that point the dye and developer combine and show colour; when the solvent melts they separate and the colour fades. The melting point sets the activation temperature.
Choosing the temperature
Cold-activated grades (around 10 to 15 °C) show colour in the fridge; body-heat grades (around 31 °C) respond to touch; hot grades (around 45 °C and above) warn of heat. Colour change happens over a few degrees, not at a single point.
Handling rules
- Keep processing temperatures within the capsule's limit, usually below about 200 °C for short times
- Avoid strong solvents and high-shear grinding that break capsules; stir in at the end
- Protect from UV: thermochromics have limited light fastness, so use indoors or under a UV-absorbing layer
- Print on a light background so the change is visible
