Liquid crystal thermochromic paint formulas initially take on a black hue. A change in temperature changes the crystal structures, which affects how they reflect or absorb light waves. This makes the paint color appear to change across a wide spectrum of colors. Manufacturers can create formulas that change color through a range of temperature fluctuations, which is known as the "changing range" or the "temperature range." The paint returns to black when the temperature dips below or above the manufacturer's formulated range.
Leuco dye thermochromic formulas start out looking clear. Manufacturers mix leuco dyes with different chemicals that react and change color with the application of heat. Surfaces painted with these formulas return to the original paint colors once they are cooled.
Dye and chemical formulas used in photochromic paints begin in a clear state, and adopt other pigments because of molecular changes that occur when the compound is exposed to heat or ultraviolet (UV) light/radiation. Manufacturers can make these paints reversible or irreversible.
Thermochromic and photochromic paints are commonly used in crafts, but they can also appear on or in a wide range of products such as mugs, clothing, eyeglasses, nail polish and toys.
Many color changing paints contain toxic or hazardous chemicals or components, and they should only be used in well-ventilated areas.