Color Matching

Q. We have an accepted color that we are using for a dyed anodized finish on 6061. Over the years, the approved color somehow went from an original production run coupon to a standard Pantone color. Unfortunately, the Pantone color doesn’t match the approved color, and we have been struggling with this for years. We would like to find the Pantone color that matches the parts we have and then incorporate this into a process specification. What’s the best way to do this? Pantone charts are fairly expensive, and there are so many that it becomes confusing very quickly. P.V.

A. Rather than fussing with Pantone color charts, I would either use the original color samples or make new ones that you can live with. Process samples for light and dark range limits, and then incorporate those color range samples into the spec. If you make new samples, use a large enough sheet or extrusion so they can be cut into several pieces. Label each coupon with the appropriate information, including the date. Assign a serial number to each or to the lot, and put several sets away in a box or envelope and keep out of the light. That should give you several years’ worth of good samples.

Pantone colors are based on the CMYK (cyan, magenta, yellow key) system of colored inks. I believe these are not suitable for matching anodized colors. I realize there is also an RGB (red, green, blue) color chart that Pantone has subsequently produced, but I still think using the actual anodized and dyed color range samples is the best way to go.

The RGB system does not really match the metallic colors produced by anodizing and dying. Even the so-called “tri-stimulus” RGB color measurement instrument systems don’t do a very good job of reading a color or a color match for anodized colors, in my opinion. I always prefer production-run anodized and dyed, light and dark range sample coupons, with the color-reading instrument being the human eye, to any other system. I’m sure folks have differing opinions about this.