Thermochromatic ink
Thermochromatic ink is a type of dye that changes color when temperatures increase or decrease. Often used in the manufacture of many toys or product packaging, as well as thermometers. Thermochromatic ink can also turn transparent when heat is applied, an example of this type of thermochromatic ink is found on corners of an examination mark sheet. This proves that the sheet has not been edited or photocopied, and also on certain pizza boxes to show the temperature of the product.
See also
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