Color Measurement Moves Forward

Companies can now afford to continually monitor processes on the factory floor rather than relying only on occasional sampling.

New technologies are keeping pace with the challenges of measuring the color of sophisticated coatings used by automotive suppliers. Source: X-Rite Inc.

Luckily for quality control personnel, new technologies are keeping pace with the challenges of measuring the color of metallic flake, pearlescent and other sophisticated coatings used by automotive suppliers, appliance manufacturers and other consumer product manufacturers.

Likewise, instrument manufacturers also have developed relatively low cost, noncontact in-line devices that measure traditional paints and coatings so companies can now afford to continually monitor processes at a particular piece of equipment on the factory floor rather than relying only on occasional sampling in the laboratory.

In the past, manufacturers that used lab-confined spectrophotometers often took samples only at the beginning, middle and end of the production runs because of the effort and expense involved in the measurement process.

New 45/0 degree geometry spectrophotometers can accurately control the quality of color by measuring a wide range of wet and dry samples without touching test surfaces.

One new type of instrumentation can measure test surfaces of materials such as powders, liquids, pastes and leathers in their natural, unaltered states to yield better, “truer” results. Unlike handheld or benchtop spectrophotometers used in laboratories that must physically contact the sample with the viewing port, these instruments measure any sample accurately from a distance of about 38 millimeters, or 1.5 inches.

In addition to targeting samples precisely, the new generation of 45/0 degree geometry spectrophotometers has advanced optics and sensors that accurately measure gloss as well as colors. Using computer software, the instrument can compensate for the difference in appearance between dry and wet samples.

Instrument makers have battle hardened spectrophotometers to withstand fluctuating temperatures, vibration, high humidity and variable lighting conditions found on the factory floor through the use of light emitting diodes (LEDs) and other technologies. By using LEDs, the instrument also can detect and ignore ambient light such as incandescent, fluorescent or sodium vapor illumination that can greatly affect results.

But spectrophotometers certainly are not the answer for every color measurement application. In cases where precise color measurement is not required, other families of instruments can represent a cost-effective solution for the control of color quality.

For instance, colorimeters are simpler and less expensive instruments that use red, green and blue filters that emulate the response of the human eye to light and color. These instruments are used effectively for sorting and quick in-line checks for less precise jobs.

A good visual analogy to compare the scale of resolution of a colorimeter with a spectrophotometer is this: if a colorimeter measures on the scale of inches, a spectrophotometer will measure on the scale of 1/16 of an inch. There are many applications in everyday manufacturing where a colorimeter is perfectly adequate to the task and a spectrophotometer would be considered overkill.

To help select the right instrument, a company should ask: What exactly is the specification that my customer wants, or more appropriately, what are they willing to pay for? Source: X-Rite Inc.

To help select the right instrument, a company should ask: What exactly is the specification that my customer wants, or more appropriately, what are they willing to pay for?

Here are a few considerations that can get a manufacturer on the road to determining the best equipment for the job:

  • Which color scale does the customer use? Instruments essentially assign numerical values to the three basic elements of color: hue, chroma and value. There are three common standards that communicate a particular color in the vast universe of possible colors: CIE Xyz, CIE L*a*b* and CIE L*C*h°.

  • What level of spectral resolution does the customer require? For instance, RGB instruments that can only give a relative nonstandard value, colorimeters that give one of the above mentioned standard values with moderate accuracy, or 31-point spectrophotometers that give all the standard color values plus full reflectance curve data and do so at a high level of accuracy?

  • How tight is the color tolerance that the customer uses? Wide open tolerances may require only a simple RGB instrument, while tight tolerances may require a 31-point spectrophotometer.

  • How smooth is the surface you are measuring? Does it approach the brilliance of a first-surface mirror or it is rough as a roofing tile? Some textured surfaces such as cloth are angularly sensitive, meaning that the color measurement is affected strongly by the orientation of piece.
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