Setting Tolerances for Color Control 11

An example showing the ∆E for the L*a*b* color system. Photo courtesy of BYK-Gardner.

An example showing the ∆E for the L*a*b* color system.
Photo courtesy of BYK-Gardner.

A well-known, if extremely rough, convention in the world of color measurement says that in CIEL*a*b* or CIEL*C*h space, a dE* value of less than one indicates that two colors are visually indistinguishable to the human eye. The reality is far more complex than this. The limits of visual perception actually differ depending upon which portion of color space is being discussed.

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Understanding CIE Illuminants and Observers 12

A standard illuminant and observer are required in order to obtain color readings. Photo courtesy of BYK-Gardner.

A standard illuminant and observer are required in order to obtain color readings.
Photo courtesy of BYK-Gardner.

Color instruments and software packages all contain references to CIE standard illuminants and observers. What do these terms mean and how are they used in practical color evaluations? The CIE (from the French Commission Internationale de L’Eclairage), or International Commission on Illumination, is the worldwide authority on how we see and measure color. BYK-Gardner uses many of these standards in its instruments and available software packages. This paper will give some easy to understand explanations of these standards and how they should be used.

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How Do I Test Tint Strength? 1

The tint strength of a paint batch is probably the single most overlooked quality to check. If the paint is going to be tinted in a store or in the plant, even a small variation in tint strength between one batch and another can result in costly touch-up complaints or wasted gallons due to a mistint.

Drawdown of paint sample.  Photo courtesy of BYK-Gardner.

Drawdown of paint sample.
Photo courtesy of BYK-Gardner.

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What Angle to Measure Gloss 6

micro-gloss and samples. Photo Courtesy of BYK-Gardner.

micro-gloss and samples. Photo Courtesy of BYK-Gardner.

Gloss

Gloss is an optical phenomenon caused when evaluating the appearance of a surface. The evaluation of gloss describes the capability of a surface to reflect directed light. A gloss meter measures the specular reflection. The intensity of the reflected light is dependent on the material and the angle of the illumination. In order to obtain a clear differentiation over the complete measurement range from high gloss to matte, 3 geometries (ranges) were defined.

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What is Metamerism? 3

Metamerism is a visual phenomenon which can be caused by a number of different factors. The result is that two samples may look the same under some conditions and different under others.

The most common cause of metamerism is that the pigmentation used to make a match is different than that found in the standard. The spectral curves are different even though the L*a* b* values are the same. The effect of different light sources reflecting off of the different materials results in a visual color difference between the two under some lighting conditions.

 

Illuminant metamerism occurs when a pair of materials appear to match when viewed under one light source, and then appear to mismatch when viewed under a second light source. Metameric pairs have spectral curves, that cross at least three times.In instrumentation the MI (Metamerism Index) is used.  Photo Courtesy of BYK-Gardner.

Illuminant metamerism occurs when a pair of materials appear to match when viewed under one light source, and then appear to mismatch when viewed under a second light source. Metameric pairs have spectral curves, that cross at least three times.In instrumentation the MI (Metamerism Index) is used.
Photo Courtesy of BYK-Gardner.

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Analyzing Color: 45/0 versus Sphere SPIN Color Instrumentation 4

In the color industry, there are two classes of instrumentation based on their geometry that are used to measure color: “45/0” and “Sphere”.

45/0 Color Instrument

A 45/0 color instrument is used in situations where we want to measure color the way our eye sees color. Gloss levels influence the way our eye sees color. A high gloss sample appears darker to our eye than a matte gloss sample with the same pigment concentration. A practical use for a 45/0 color instrument is to check color consistency of consumer products when appearance is a deciding factor in a product purchase.

45°circumferential illumination 0° viewing perpendicular to sample plane This simulates visual color evaluation by excluding the gloss. The advantage of circumferential illumination is to achieve more repeatable measurements results on directional and structured surfaces. Photo courtesy of BYK-Gardner.

45°circumferential illumination
0° viewing perpendicular to sample plane
This simulates visual color evaluation by excluding the gloss. The advantage of circumferential illumination is to achieve more repeatable measurements results on directional and structured surfaces.
Photo courtesy of BYK-Gardner.

So for a 45/0 color instrument,

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Controlling the Tight Color and Gloss Tolerances of Automotive Interior Parts 5

Measuring color for an interior automotive application with a spectra-guide-S. Photo courtesy of BYK-Gardner.

Measuring color for an interior automotive application with a spectra-guide-S.
Photo courtesy of BYK-Gardner.

Automotive Interiors

Automotive interiors are comprised of a variety of materials and produced by several companies. To achieve a uniform appearance, automotive companies have tight quality control (QC) tolerances. Color tolerances are typically ­±0.5 for ΔL*, Δa*, Δb* and gloss tolerances are typically ±0.3 to 0.5 gloss units (GU).

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The Importance of Measuring Color and Gloss for Weathering 2

Samples undergoing a weather test.

Samples undergoing a weather test.

Weathering is a routine performance test to determine durability of paint and plastics under extreme weather conditions. The most popular areas for weathering studies are located in AZ and South FL. Samples can also be placed into chambers that can simulate changes in temperature, humidity and UV levels. More…