Thermochromatic Ink
Security ink with a normal "trigger" temperature of 88 degrees F, which will either disappear or change colors when the ink is rubbed, usually by the fingertips.
Read more about this topic: Security Printing
Famous quotes containing the word ink:
“Traveling takes the ink out of one’s pen as well as the cash out of one’s purse.”
—Herman Melville (1819–1891)