Thermochromic (TC) Products predominantly change color in response to temperature fluctuations. There are two primary types of TC; liquid crystals and leuco dyes. The most famous TC application ever, the "mood" ring of the 1970’s, was a liquid crystal. Today, liquid crystals are used in many products, including forehead thermometers, room and refrigeration thermometers and other applications including food quality indicators. While liquid crystal TCs are extremely capable materials, they are difficult to work with and require highly specialized manufacturing techniques. The other type of TC is called a leuco dye and is commonly used in manufacturing and control process, advertising, consumer packaging, product labels, security printing, novelty applications such as temperature sensitive plastics and mugs, promotional items,toys and textiles. Thermochromic permanent change ink is a high temperature activated, permanent change pigment used in metalworking,annealing, welding and riveting for quality purposes.