Thermochromes, Pellets & Seger Cones

  • Physical characteristics like color, shape, reaction, luminous flux, melting point etc can be used to determine temperature.
  • Crayons marked-labels and paints applied by brush or spray, change their color & luminescent material change their brightness when certain temperature is reached.
  • Some may go with single change in color, some may undergo several changes at different temperatures.
  • Ceramic industry prepare cones made up of mixtures of material having any pyrometric value. A temperature comes when cone bends to touch base gives temperature for what cone was prepared.
  • Pellets posses metal & metal alloys which melt at their melting point.
  • Paints & crayons can indicate up to 650° C.
  • Temperature indicating pellets can indicate up to 1600° C.
  • Seger cones can indicate up to 2000° C.


  • Easy visual observations.
  • Low cost detection of temperature.
  • Relatively inexpensive.


  • Not recommended for hot gases, gases like ammonia, CO2, water vapor form colorful salt by chemical reactions.
  • Use integrally with image processing for transmitting temperature adds to cost.
  • Color Indicators retain for specific time period.
  • Material sticks tightly to surface where crayons & paints are marked.