We frequently get calls from customers who can’t figure out why their measurements vary, even when they’re using maintained devices. Why would a sample read one way one day, then slightly different another? Many times the culprit is thermochromaticity, and it becomes an even bigger problem as the seasons change.
Every kind of material changes color with temperature. These changes cause the material to exhibit a shift in reflected wavelengths of light, which can alter our perception. Often the color shift is so slight the naked eye would never notice. But if your job is to quality check color critical products, you need to fully understand how thermochromaticity can impact your color, your measurements, and your ability pass inspection.
What types of materials are impacted by thermochromaticity?
From dyes to ceramics to plastics, most materials and colors are vulnerable. Unfortunately there’s no analogous way to predict which colors will change, and by how much. You have to test your materials to gauge their reactions.
Some manufacturers are even using thermochromaticity to their benefit, creating fun products like color-changing nail polish, t-shirts, and drinking cups.
How much temperature change does it take to shift a color?
Thermochromaticity is material and color dependent. For instance, on the low end we can measure a color difference after a temperature change of just 5° Fahrenheit on a ceramic tile. For print media on corrugated cardboard, it may take more of a shift to notice a difference
To illustrate the impact of thermochromaticity on a ceramic sample, I conducted an experiment with the green tile that comes with many of our industrial devices. First, I measured it at room temperature to create the standard. Then I popped it in the freezer until it reached 35° F. I then used the Ci7860 to measure it every few minutes as it came back to room temperature. This table shows how the rising temperature impacted the tile’s color.
After a shift of 2.9°, the measurement moves from passing to marginal. After a shift of just 5.9°, the measurement fails. Think of this in practical terms… this color would pass if measured in a lab that is 72° but not in a lab that is 68°!
Who is most at risk for thermochromaticity?
Here are the most common scenarios where thermochromaticity can cause an issue:
1 – Changes in seasonal climate.
If you work in a region that experiences temperature shifts as the seasons change, you need to be aware of thermochromaticity pitfalls. Let’s say you target a standard in the summer when the inside of your lab is 85°. Once it turns winter and the inside temperature drops down to a balmy 65° in the mornings, you might suddenly start jumping over tolerance. Even if your facility is climate controlled, you can still run into issues if you’re measuring incoming raw materials on the dock in less than ideal conditions.
2 – Companies with multiple branches.
This is especially true if the branches are in different climate regions. Even if they’re all measuring the same digital standard using certified instruments, if one is measuring in an 85-degree factory and another in a 70-degree lab, thermochromaticity may cause a difference in readings.
3 – Measuring samples at different stages of cooling.
Take plastic film, for example. If you measure it when it’s coming out of the extruder, you’ll certainly get a different measurement after it cools to room temperature. If you pass tolerance when the film is warm, but the customer verifies the shipment at room temperature, it likely will not pass inspection.
4 – Sourcing from uncontrolled locations.
If you source raw materials from uncontrolled locations, be aware of potential fluctuation in readings due to poor environmental control.
Overcoming thermochromaticity through stability
This doesn’t mean you can’t measure at an elevated or decreased temperature, or work with suppliers in different climate zones. It’s all about consistency. If you start measuring in an 85-degree environment, you need to stay at that temp or find a way to compensate for differences.
Many of our newer X-Rite devices prompt for recalibration when the internal device sensors detect a temperature shift. We also ship a green tile with our newer industrial instruments. Although it’s most commonly used to check instrument drift, it’s also a great way to measure thermochromaticity.
Get in touch if you want to learn more about how to evaluate thermochromaticity in your workflow. And be sure to share this information with everyone involved in your color workflow!