Color standards, availability

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. 

The basic resin for EPS is in the form of beads that ate expanded to a desired density before molding. Densities for packaging parts are typically 20—40 kg/m. Once expanded, the beads are fused in a steam-heated mold to form a specific shape. Most parts are molded of standard-white resins, although several pastel colors are available. 

Availability of Color Standards. The USDA orange juice color standards cited in this section are official color standards. Information regarding the color standards and their availability may be obtained from ... 

Apparatus Use a Lovibond tintometer or the equivalent and a set of color comparison glasses that conform to the AOCS-Wesson Tintometer Color Scale (available from the National Institute of Standards and Technology). A minimum set of glasses consists of... 

TLC. The paprika color in 42 samples from commercially available foods, that had a label stating the use of paprika color, were analyzed by CIS TLC to examine the influence of the coexisting substances from the sample on the Rf value. The obtained Rf values of the main spot (Rf=0.50) of saponified paprika color were then compared, and Ra/Rs value was computed. The average Ra/Rs value was 1.01 with a coefficient of variation of 2.6%, suggesting that the spot extracted from the samples appear nearly at the same position as that of the paprika color standard without being affected by contaminants in the sample and that the identification of the color is reliable and reproducible. 

Correlation was established between the colors of food samples measured by the colorimeter color and the color machine vision system. The correlation coefficients between L a b color parameters for beef and carrots obtained from the two instruments can be seen in Table 2. For all the data collected, a high correlation was observed (R > = 0.98). The established correlation makes it possible to verify CMVS s color measurement accuracy of colors that are not available from published color standards. Furthermore, the correlations between the CMVS and colorants in food systems can also be inferenced based on established correlations between colorimeter measurements and colorant contents. 

Bromine ttifluoride is commercially available at a minimum purity of 98% (108). Free Br2 is maintained at less than 2%. Other minor impurities are HF and BrF. Free Br2 content estimates are based on color, with material containing less than 0.5% Br2 having a straw color, and ca 2% Br2 an amber-red color. Fluoride content can be obtained by controlled hydrolysis of a sample and standard analysis for fluorine content. Bromine ttifluoride is too high boiling and reactive for gas chromatographic analysis. It is shipped as a Hquid in steel cylinders in quantities of 91 kg or less. The cylinders are fitted with either a valve or plug to faciUtate insertion of a dip tube. Bromine ttifluoride is classified as an oxidizer and poison by DOT. 

Color Vision Defects. Anomalous color vision is present, eg, if one of the three sets of cones is iaoperative (dichromacy) or defective (anomalous trichromacy). This affects 2—3% of the population with males mote prone because these defects reside on the X-chromosome, with one present ia males but two ia females. Eye specialists have standard tests for detecting these and other defects. Summaries of this whole field are available (6,9,22). 

The paper. strips used in the colorimetric method are impregnated with such dyes that the color of the test paper is dependent upon the pH of the medium in which the paper is placed. A standard color chart is supplied for comparison with the test strip. Test papers are available in a wide range type, which permits estimating pH to 0.5 units, and in narrow range papers, with which the pH can be estimated to 0.2 units. 

The method, obviously, is subjective, the precision and speed of the match depending upon the observer and his experience. Results on foods have usually been expressed in terms of color disks, which are different for each product and which must be carefully standardized. [Conversions to standard colorimetric systems of notation can be made (12), provided suitable colorimetric data are available for the disks used.] Furthermore, instruments suitable for the most precise work by this method are not at the present time commercially available. 

Conversion tables and charts now available make it possible to express I.C.I. data in forms in which a specified color and the significance of measured color differences can be more easily visualized. For example, I.C.I. values calculated from objective instrumental readings can be converted into the Munsell notation which evaluates the three psychological color attributes—hue, lightness (Munsell value), saturation (Munsell chroma)—on scales of approximately equal visual steps. In addition, the Munsell color charts offer one of the most convenient sources of material standards for direct color comparisons. 

Colors in a laboratory should be coordinated, just as in a home. If pre-finished work benches are to be installed, they might set the color scheme. While they are available in several colors or combination of colors, the choice is not unlimited. In one case, the laboratory operator was color blind, so his wife took over the job as decorator. First, she selected a two-color scheme for the work benches. Color chips in hand, she then chose a floor covering from a number of samples submitted. For the wall paint, she found a standard color of the recommended quality that harmonized with the cabinets. A few appropriate charts and a colorful cloth wall-hanging of pipes and valves completed the decor. The result received many favorable comments from visitors to the facility. 

However, these analogues are actually hypothetical. The reason for this is that it is nearly impossible to obtain optical measurement components, such as the source and the detector, whose response to light across the visible spectrum is flat (or nearly so). However, this is not an impossible task and we find that an excellent match can be obtained to the transmission functions of 7.8.21., i.e.-those of the Standard Observer. This is typical for commercially available instruments. Now, we have an instrument, called a Colorimeter, capable of measuring reflective color. 

---