Color matching

Similar colors are Hsted horizontally but are not exact color matches. 

Color Matching. Color matching is a process in which a technician prepares a formulation, ie, a mixture of pigments in a desired medium, that has the color effects desired by the customer. A good color match in one medium, eg, plastic, is not always a good match in another medium, eg, ceramic glaze. Thus the medium as well as the processing conditions have to be identical to those used by the customer. 

Experienced color matchers can achieve a good color match by trial and error without using any instmmentation. In some cases, however, this technique can be a lengthy process, and should the desired match be outside the color space defined by the available color standards, the technician might spend too much time just to determine that the match is not possible. To get the most cost-effective match using a low metamerism in the shortest possible time, the use of a computet color matching system is preferable. 

Color Mixing. The various types of dye powders used to make dye stains are blended to achieve the desired color. Most finishers purchase wood stains premixed to specified colors. In the wood-finishing industry, various shades of brown are the most common. These colors are usually blended from primary colors. Color-matching skills can be acquired only by practice, but the basic theory of color matching is relatively simple and easily understood. The basic theory of color matching can be demonstrated by using the color circle shown in Figure 1 (see Color). 

Acceptance of a color recommendation made by the coatings suppHer effectively eliminates the time and cost involved in an initial color match and ensures selection of a pigment combination appropriate to the coating use. If, however, a coatings user provides a sample or standard for a color match, formulators need the foUowing information. 

Automotive Refinish Paints. Paint for appHcation to automobiles after they have left the assembly plant is a significant market. Although some of this paint is used for fuU repainting, especiaHy of commercial tmcks, most is used for repairs after accidents, commonly just one door or part of a fender, and so forth. In order to be able to serve this market, it is necessary to supply paints that match the colors of aH cars and tmcks, both domestic and imported, that have been manufactured over the previous ten years or so. Repair paints for the larger volume car colors are manufactured and stocked, but for the smaller volume colors formulas are suppHed by the coatings manufacturer to the paint distributor that permit a reasonable color match for any car by mixing standard bases. 

Clearly, standardized light sources are desirable for color matching, particularly in view of the phenomenon of illuminant metamerism described below. Over the years CIE has defined several standard illuminants, some of which can be closely approximated by practical sources. In 1931 there was Source A, defined as a tungsten filament incandescent lamp at a color temperature of 2854 K. Sources B and C used filtering of A to simulate noon sunlight and north sky daylight, respectively. Subsequently a series of D illuminants was estabUshed to better represent natural daylight. Of these the most important is Illuminant E). ... 

The ready availabiUty of computers has led to the detailed analysis of the colorant formulation problems faced every day by the textile, coatings, ceramics, polymer, and related industries. The resulting computer match prediction has produced improved color matching and reductions in the amounts of colorants required to achieve a specific result with accompanying reductions of cost. Detailed treatments have been given for dyes and for pigments (13,29,30). 

Finally, it cannot be overemphasized that despite instmmental measurements and data manipulations, it is the perception of the eye that still is the final arbiter as to whether or to what degree two colors match. Instmmental methods do serve well for the typical industrial task of maintaining consistency under sufficiently weU-standardized conditions however, a specific technique may not serve in extreme or unusual conditions for which it was not designed. 

Colorimeters. Also known as tristimulus colorimeters, these are instniments that do not measure spectral data but typically use four broad-band filters to approximate the jy, and the two peaks of the x color-matching functions of the standard observer curves of Figure 7. They may have lower accuracy and be less expensive, but they can serve adequately for most industrial color control functions. Examples of colorimeters are the BYK-Gardner Co. XL-835 the Hunter Lab D25 series the Minolta CA, CL, CS, CT, and CR series (the last of these is portable with an interface) and the portable X-Rite 918. 

Color-order systems, such as the many MunseU collections available from Macbeth, have been described previously. Essential for visual color matching is a color-matching booth. A typical one, such as the Macbeth Spectrahte, may have available a filtered 7500 K incandescent source equivalent to north-sky daylight, 2300 K incandescent illumination as horizon sunlight, a cool-white fluorescent lamp at 4150 K, and an ultraviolet lamp. By using the various illuminants, singly or in combination, the effects of metamerism and fluorescence can readily be demonstrated and measured. Every user should be checked for color vision deficiencies. 

For RRIM-based composites, the main benefit is the case with which the properties can be varied across a wide range. Decorative finishes can be applied to RRIM molding by painting or, where color matching between components is less important, by self-coloring. However, color coating of the mold surface prior to RIM provides a better finish. 

The C1E color coordinates are obtained by a similar procedure, repeating the convolution for each of the tabulated color matching functions that describe the response of the ideal observer s blue, green, and red cones (b, rA). 

It is desirable for the record to have an objective statement of the nature and degree of color deterioration. The simplest, but least desirable, method is comparison of sample color with color charts or plates such as those used in the Munsell system, Ridgeway s color standards, or the Maerz and Paul dictionary of color. Such a method is limited in value because of the difficulty of obtaining true color matches, and because of variations due to human error. The use of color charts or plates may be much improved in the Munsell system by employing a disk colorimeter (29). Kramer and Smith (21) have pointed out that the results obtained in its application to foods are sometimes difficult to explain and compare, and that the method requires special training of the operator and is tedious and cumbersome. 

The method is proposed by Hartl et al. [19-21]. The colorimetric interferometry technique, in which him thickness is obtained by color matching between the interferogram and color/fllm thickness dependence obtained from Newton rings for static contact, represents an improvement of conventional chromatic interferometry. 

IV. Color Processes and Color Matching STOtems In terms of color, we can have one of two processes ... 

Since color matching is meant for humans, it is natural to define color in terms of an average, or "Standard Observer". Our first step is to build an instrument which contains three colored lamp sources, a place for the individual observer, intensity detectors, and a monochromator, as shown in 7.8.19. on the next page. 

A system for emittance color matching is given in the following ... 

Nevertheless, it is well to note that it was the subjective observation of the lack of correction for luminosity in the Munsell System that gave impetus to the development of the CIE Color System. The major problem vidth the Munsell system was that each person attempting to match colors did not produce the exact same result. So color matching became dependent upon the person. 

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