Thermochromism: The Effects of Temperature on Ceramic Products

During manufacturing and production processes, products can be exposed to varying temperatures of heat. Using heat or high temperature is a common practice in manufacturing, ceramics for example, go through a heat-treatment also known as sintering or firing to produce the finished product. Elevated temperatures can have both permanent and temporary effects on a product’s physical appearance, particularly color. Color change due to temperature, known as thermochromism, is a major color issue faced by many producers.

A pigment or dye’s reaction to high temperature depends on its chemical properties and material. Too hot of temperature or long exposure to high temperature may completely degrade the color of an object. In other instances, an object or sample changes to another shade of color until it stabilizes back to room temperature. Certain colors are more susceptible to this drift, depending on the application.

The industry mentioned earlier in this article, Ceramics also provides a good example of thermochromism. After heat-treatment, a ceramic sample is removed from the oven and set aside to condition or cool down to ambient temperature. During this “drying-time”, manufacturers may notice a change in color.  Because of this temporary drift in color, evaluating the sample against the standard during this “cool down” stage will deliver misleading results.

Due to the misleading results encountered during the “cool down” stage, both quality control and process control should require that a product meets a defined color standard through an efficient procedural process. The procedural process defines how the product is to be evaluated, when or how often it should be inspected, and the steps to be taken for troubleshooting color inconsistencies.

Even after processing, the color of a sample could drift to another shade or color for a certain period of time. It is recommended to assess the sample at scheduled times and record how long it takes to cool down and adjust to its correct color. Once the sample is stabilized to ambient temperature, visual and instrumental evaluations can be performed more accurately to identify if the sample color meets the standard.

The CM-700d is a well-known spectrophotometer in the ceramic industry. The portable instrument’s vertical design makes measurement easy for a wide variety of surfaces commonly used in ceramic products. For accurate color measurement, a sample should be at a stable temperature to avoid color changes due to thermochromism. Color measurements should also be taken in a temperature-controlled room. Both the sample and the spectrophotometer should be kept in the controlled room for a period of time where they can both acclimate to the ambient temperature, and then more accurate measurements can be taken.

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The technological leader in color and light measurement solutions, Konica Minolta Sensing Americas helps organizations formulate, evaluate, and control color to meet product quality and operational goals more efficiently.

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