- 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.