October 9, 2015
Have you ever tried to describe a color? Doing so is almost impossible without a visual reference. You can try to explain that it’s a few shades darker than the red stripe on someone’s shirt, or a tad lighter than the green coffee mug on the desk. But you still can’t fully and accurately describe a color. Now imagine you’re working with your colorant supplier, except in this situation, an entire shipment of coatings is on the line. Get the color wrong, and you’ve potentially lost thousands of dollars in inventory – not to mention the trust of a customer that you must tell about the botched order that needs to be redone.
It is imperative that coatings manufacturers and colorant manufacturers understand each other when it comes to color. That means speaking the same language, and using instrumental color measurement provides that language. There are numerous color spaces that could be used to communicate in; the important point to remember is to identify the color space being used. For the purposes of this article, the 1976 CIE L*a*b* (CIELAB) color system will be used, as it is the predominant color system used to describe, match and control color in the Coatings Industry.
What is the CIELAB color space, and what else do you need to know about communicating color? Here’s a look.
What CIELAB is
CIELAB is an opponent color system that can pinpoint the exact coordinates of a specific color in three dimensions. Three perpendicular axes, named L*, a* and b*, pass through the space. The L* axis passes through vertically and indicates lightness – from pure white at the top to pure black at the bottom. The remaining two axes pass through horizontally. The a* axis indicates a progression from red (+) to green (-), and the b* axis a progression from yellow (+) to blue (-).
CIELAB values can also be expressed in L*, C* and h° values, where C* indicates chromaticity, or color saturation, and h° represents the hue angle around the horizontal axes – much like a 360-degree color wheel.
What else is needed to communicate color
For communicating color, the other color parameters used in the measurement need to be stated. These include the observer, geometry of the instrument, if any color tolerancing is in use and the illuminants.
Illuminants are critical for color communication for both instrumental and visual assessment. In the Coatings Industry, Daylight 6500°K is usually the primary illuminant used for color viewing. It is also important that additional light sources be used if for use other than exterior applications.
The geometry of the instrument used will determine if either the color or the appearance is being communicated. For instance, a sphere geometry spectrophotometer with the specular included measures the color, because light is not exiting, whereas, with the specular excluded, some light does exit depending upon the surface characteristics of the color being measured, which then is communicating the appearance of the color. There are advantages and disadvantages to using both; it is just critical to communicate what is used and check that the right geometry is being used for a specific need.
Who needs to know it
Manufacturers of all sizes should have a number of key people who are well educated in instrumental color measurement. Besides coating formulators, chemists in the testing lab and any other team members who are involved in the quality control process, it is also critical for marketing and sales teams to know color space well enough to discuss it with their customers.
Ultimately, the more people who can speak the language of instrumental color measurement, the more cohesive the manufacturing and sales process will be, from the colorant supplier to the coatings company to the customer that ultimately uses the coatings.
With that in mind, colors still need to pass the eyeball test as a check and balance against potential inaccuracies that may occur in color measurement. Remember, instrumental color measurement is a tool. If a color doesn’t look right when viewed under the specified light source(s), don’t just trust the numbers – examine the matter more thoroughly.
Chromaflo Technologies is a leading provider of high-quality colorant technologies for the architectural and industrial coatings industries. Contact us at (440) 997-5137 to discuss your colorant requirements.