Page:NBS Circular 553.djvu/18

 closer to 4 than 6, and is estimated as 4.6. Now compare the sample with the two Munsell 7/4 standards. Suppose that its hue is seen to be nearer to that of the 10YR chart than the 7.5YR chart, say 4/5 of the hue difference between the charts or 2 hue steps from the 7.5YR and one-half hue step from the 10YR chart, or at 9.5YR. Now inter- change the positions of the charts and check the Munsell notation. If these are found to be un- changed, the final notation is 9.5YR 7. 2/4. 6. If for greater accuracy the Munsell renotation is desired, it may be found by the method outlined in 6.1.3 above.

The color name corresponding to the Munsell notation is found by selecting from the color -name charts the one that contains 9.5YR (page 21, see hue designation 8YR-1Y near the upper right-hand corner). Plot 7.2 value and 4.6 chroma on this chart. It falls in the block named light yellowish brown (see point ⊙ plotted on chart 8YR-1Y, p. 21); so this is the color designation of the sample. The Munsell renotation corresponding to this notation is 9.3YR 7. 4/4. 5 and the color designation is the same.

6.2. Opaque Solids

6.2.1. Comparison with Munsell Color Standards. Hold the sample in the fingers, or in tweezers if the sample is small, a short distance above the chart or charts and move it about for comparison with the Munsell color standards. Care should be taken not to cast a shadow on the standard with which the sample is being compared (see fig. 6). The amount of handling required for the comparison, and consequent soil and wear on the standards, will be diminished if the charts are arranged in hue sequence on the table or desk. If the sample is large and flat., it will facilitate the comparison if a small neutral gray shield with the usual sized rectangular opening is placed over the surface.

6.2.2. Lighting and Viewing Conditions. The sam- ples are to be illuminated at 45° by daylight (see section 6.1.2) and viewed along the perpendicular to the surface. Since the samples are held above the plane of the color standards, it is important that the illumination on the two horizontal planes be as nearly the same in amount and quality as possible. Care should be taken to hold the surface of the sample in the horizontal plane and close to the plane of the standards; errors in Munsell value by as much as a whole step are possible through inadvertent tilting or raising of the sample surface. If a source of artificial daylight such as in figure 4 is used giving a diffused even illumination over a large area from above, or if the comparison is made out of doors by diffuse light from a large part of the sky, the position of the sample with respect to the light source is less critical.

For minimizing the troubles due to uneven illumi- nation on samples such as rods (pencils, twigs, roots) having approximately cylindrical surfaces, it is recommended that the axis of the cylinder be held horizontal and pointed in the direction of the light source so that neither side of the sample is shaded.

For samples having glossy surfaces the use of a black canopy or curtain will be required as described in section 6.1.2.

The color of such a sample may be designated either by giving the average color found for the sample or by giving the color names corresponding to the complete color range. This range may be in hue, lightness, or saturation, or a combination of two or all of these. Color ranges involving chiefly variations in lightness and saturation can often be conveniently indicated by the unmodified name, such as orange, by which is meant the color range covered by the designations light orange, brilliant orange, moderate orange, strong orange, vivid orange, and deep orange (see charts covering Mun- sell hues 2YR to 7YR).

6.2.3. Nonmetallic Samples With Matte Surfaces. Proceed as in 1 and 2 above. The recommended angles of illumination and viewing need not be as strictly followed, because the appearance of a matte surface does not change importantly with small variations in these angular conditions.

6.2.4. Glossy Surfaces Having No Regular Detailed Structure. Samples of vitreous enamel and smooth paint films are often found with glossy surfaces having no regular detailed structure. Proceed as in 1 and 2 above, giving particular attention to the prescribed angles of illumination and viewing. The characteristic color of the sample is obtained only when specularly reflected light is prevented from reaching the eye of the observer.

6.2.5. Glossy Surfaces Made Up of Cylindrical Elements. Samples of satin-finish textiles and glossy brush-marked paint films may be considered as made up of cylindrical elements. Proceed as in 1 and 2 above. It is not always possible to prevent light from being specularly reflected from such glossy surfaces into the eye of the observer; but by so orienting the sample in its own plane that the specular component is reduced to a minimum, the most characteristic color of the sample is usually obtained. Some textiles require more than one angle of view or illumination to bring out the characteristic color or colors; changeable silks are extreme examples of such textiles.

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