Thermal printing is a digital printing process which produces a printed image by passing paper with a thermochromic coating, commonly known as thermal paper, over a print head consisting of tiny electrically heated elements. The coating turns black in the areas where it is heated, producing an image.
A thermal printer
Bills and receipts are typically printed on thermal paper.
A thermal print head
Thermal print head at high magnification
Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a different color when cool enough to drink, or kettles which change color when water is at or near boiling point. Thermochromism is one of several types of chromism.
Example of a thermochromic T-shirt. A hairdryer was used to change the blue to turquoise.
Another example of a thermochromic T-shirt.