When evaluating a round of color matching, it is important to consider metamerism, a phenomenon in which certain colors can match under one light source but not under another. To avoid issues with metamerism, it is important to evaluate matches under a controlled light source that mimics the lighting the final product will be evaluated under. A color meter can confirm a color match, but never underestimate the human eye, which can also discern very minor color shifts.
Specifying a Tolerance
Color tolerance is important to specify for any project and needs to be understood by suppliers, fabricators and clients. Many fabricators use a reference color placard and a trained quality control operator to check color. To ensure that color references remain true to color, they should be stored properly to avoid sun exposure and replaced at the supplier’s recommendations.
However, simply using a reference color placard may not suffice for color critical operations, such as architectural applications and mass-produced parts mated during assembly. For color critical applications, a color meter should be used to measure color and confirm it is within tolerance.
At Kreysler & Associates, we create visual tolerance boundary samples to illustrate the maximum allowable color shifts in each direction to the customer. The samples can be measured to create a tolerance. Often times, only a lighter and darker boundary sample are made, since that is the typical color variation for us. If other shifts are expected, samples can be made that illustrate more red, green, blue or yellow shifts. Customers can then use the samples on site to confirm product conformance. Fabricators without a color meter can use the samples as an internal quality control check.
In the coatings industry, Delta E units are used to express the measure of change in visual perception of two colors. A typical tolerance that gelcoat suppliers will meet is 0.5 Delta E. Beware that color can be shifted another 0.5 Delta E just from processing variation. For most applications, a 1.5 Delta E tolerance on color critical projects is acceptable to the client, but this can be hard to meet when using multiple batches of gelcoat. When mixing gelcoat in house, color can be corrected before use, but there will still be variation from processing. Although it’s not always possible, using the same gelcoat batch for all products is a great way to minimize color variation.
Monitoring and Color Control