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The Effect of Heat Transfer on Color Change

Occurring when there is a temperature difference between two objects or areas, heat transfer is the process of moving heat from a warmer object or area to a cooler object or area. If you transfer enough heat and pressure to the right object or substance, it may cause a color change. For example, if heat is transferred from your body to a mood ring on your finger, the color of the ring changes; if you are heating a piece of steel at a high temperature, it will turn red.

Transfer of Heat Energy
- The movement of rising currents, such as steam and hot air, transfers heat energy in gas and liquids. This heat transfer process is known as convection; you witness it when you see water boiling. Conduction heat transfer occurs within a substance, or between two objects that are touching. Transporting energy such as sunlight, electromagnetic waves allow objects to absorb radiation. Radiation heat transfer occurs when you use a heat lamp, or when the atmosphere absorbs solar radiation.
Color
- The rainbow displays the spectrum of colors in white light.
  
  Your eyes, which are sensitive to light, can only see a small amount of the light transmitted via electromagnetic wavelengths. The light you can see is called visible light. The range of visible colors includes violet, blue, green, yellow, orange, red and white. White light is a mixture of all colors visible to you through light, and black has no light at all. Colors can be associated with a single wavelength; however, most colors have a range of wavelengths. The heat-transfer temperature range correlates to the visible wavelength spectrum to produce a color change.
Color Change
- Reaching the color-temperature play interval, heat at a range of temperatures can cause the structure of an object or substance to change. When the structure changes, what you will see is a range of colors reflected from light passing through the object or substance. When the heat is outside the temperature range, higher or lower, the object or substance returns to the original color. There are several substances that have the ability to change colors during heat transfer, such as liquid crystals and leucodyes. The way the heat is applied, or the variation in the color derived, may vary. However, changing color during heat transfer follows the same basic principle.
Application
- Heat transfer is used to change colors and substances in many different objects. Heat transfer is used on clothing, cups, pencils and rings that contain liquid crystals or leucodyes. The process is also used with liquid crystals to color-code the temperature for room, aquarium, and medical thermometers. Heat may be transferred from your body, an iron, pouring hot liquid in a cup, sunlight, or any number of heat sources capable of reaching the range of temperatures required to make an object or substance change colors.

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