Q. We document our color matches with a 60-degree spectrophotometer. Is a Delta E rating of less than 1.0 a good control, or is there a better way?— J.M.
A. In my past experience, I have run spectrophotometric analyses of paint samples, but I found it more convenient to use Color Drift Control cards (paint color chips) for color matching. In our paint lines at Westinghouse Electric Corp., we used the cards to check the color of each new batch of paint. Panels were spray-painted with the new paint, and the cured panels then were compared visually, instrumentally or both to the cards. The Pennsylvania Railroad and other companies also frequently used the cards for color matching, and these cards still are used to provide paint color chips to suppliers of model railroad paints, manufacturers of model railroad equipment, prototype equipment restorers and model railroad enthusiasts.
The company that produced our color cards also produces color-testing instruments that measure the color values of a sample and report them in Munsell; XYZ; and L*, a*, b* and other color notations using a computer interface. To me, these values are more convenient and meaningful than spectrophotometric curves. I suggest you investigate the use of these instruments. Suppliers of color testing instruments can be found on PFonline.com. Click on Suppliers, then Painting and then Testing Equipment, color.