These constant-value charts show at a glance for all Munsell chromas what ranges of Munsell hue are referred to by the various hue names of this system; this information is of course obtainable, though less conveniently, from the color-name charts themselves. 6. Color Designations From the Munsell Book of Color for Diverse Types of Specimens

The procedure for comparing a specimen with the Munsell Book of Color depends importantly on specimen type, whether the specimen is solid or liquid, opaque or transparent, large or small, flat or of irregular shape, and so on.

6.1. Dry Opaque Powders (Grain Size Less Than 1 mm)

6.1.1. Preparation of Sample. The sample is placed slightly heaped up in a clean holder (see fig. 3) at least 2 mm deep. Over this is placed a clear colorless coverglass about 1 mm in thickness which is pressed down with a rotary motion and held in place by friction between the holder and the coverglass mount.

For very fine powders, the pressure exerted upon the sample by the holder becomes critical and may require that a special holder be designed. In the measurement of the colors of cosmetic powders, for instance, color changes many times greater than the allowable tolerances may result from inadvertent pressure on the sample.

Since

6.1.2. Lighting and Viewing Conditions. the color designations conform to usage only for specimens viewed in daylight, this source is to be

used in the color-comparison work. A table placed by a window so that light reaches the table top from the operator's left or right chiefly from the sky and chiefly at angles centering on 45° from the horizontal is recommended. A north window is best because no special precautions are usually required to eliminate direct sunlight. A canopy of black cloth, preferably black velvet, should be hung above the sample on the side opposite the operator in such a position as to be imaged in the mirror surface of the cover glass; such an arrangement eliminates errors from unwanted admixture of ceiling light reflected from the cover glass. The sample and standard placed on the table top are viewed nearly along the perpendicular to the surfaces, that is, just enough off perpendicular to avoid having the operator's face mirrored in the cover glass. Illumination at 45° and perpendicular viewing are recommended by the CIE [53]. A skylight or source of artificial daylight (fig. 4) located above the sample may also be used, but in such an arrangement the angle of view should be approximately at 45° from the horizontal, and the black cloth should be hung vertically beside the sample opposite the observer. Perpendicular illumination with viewing at 45° gives results equivalent to the recommended CIE method.

It is important that the illumination of sample and working standards be closely the same both in amount and quality; otherwise different Munsell notations will be found by interchanging them. Even with closely uniform illumination it is good practice to make this interchange as a check during the comparison.

In any computations involving the spectral energy distribution of the source, that of standard source

FIGURE 3. Preparation of an opaque powder sample for comparison with the Munsell color scales.

Note the friction ring that fastens the cover glass to the holder. (Courtesy Munsell Color Co., Inc.)

FIGURE 4. Macbeth daylight unit mounted to give even illumination over a large area.

C recommended by the CIE [53] as representative | of average daylight is to be used.

6.1.3. Determination of a Munsell Notation or Renotation. Select the two adjacent Munsell constant-hue charts between which the hue of the sample falls. Place these on each side of the sample and cover each with a small neutral gray shield, or if using the large triple-aperture shield (shown in fig. 5), place them under the holes in the side flaps and the sample under the central opening. The Munsell hue, value, and chroma notations for a sample are found by interpolation or extrapolation among the standards of the Munsell charts; most operators prefer to estimate first the value, then the chroma, and finally the hue. This is done as follows: look at the three colored rectangles (1 sample and two standards) and see whether the sample is lighter or darker than the standards. Move the chart whose hue is nearer to that of the sample up and down from one value level to another and find the two values between which that of the sample falls. Next estimate to the nearest tenth of a value step the value of the sample relative to these two levels. Record this number in front of a shilling mark as, for example, 3.0/ or 6.2/.

Then move the charts sideways so as to present successively colors of the same Munsell hue and value but of different chroma, and by similar interpolation determine the Munsell chroma of the color. In this comparison pay chief attention to the Munsell standards having values nearest that of the sample, and secondary attention to those next nearest. Although all Munsell samples of the same chroma notation are intended to yield in daylight color perceptions of the same saturation, sometimes a slightly different estimate of chroma will be obtained by comparison with the standards of the next nearest value. In such an instance, report an average notation for chroma. Note that there are two chroma

FIGURE 5. A triple-aperture shield with sample aperture in center and apertures for Munsell standards on each side.

At upper right is shown a double-aperture shield for liquids, with vials and holder (section 6.3.2), and at upper left the pocket edition of the Munsell Book of Color. (Courtesy Munsell Color Co., Inc.)

steps between each two adjacent columns of Munsell samples. Estimate the chroma to the nearest fifth step and record this number after the value notation and the shilling mark, as, for example, 3.0/6.0 or 6.2/4.6.

Now with the corresponding Munsell standards of value and chroma closest to those of the sample showing through the apertures of the shield, estimate the hue of the sample relative to that of the two Munsell charts. Remember that each two adjacent charts are two and a half hue steps apart. Record the hue estimated by this interpolation to the nearest one-half step in front of the value/chroma designation and separated from it by a space; for example, 7Y 3.0/6.0 or 9.5YR 6.2/4.6. If the value and chroma of the sample do not correspond very closely to those of any of the Munsell standards, it is advisable to repeat the interpolation for hue with the next closest pair of standards and take an average notation for the hue.

Check the Munsell notation, particularly hue and value, with the charts interchanged.

For most color descriptions, the ISCC-NBS color names derived from the Munsell book notations as determined above are sufficiently applicable. If greater accuracy is demanded, determine the chromaticity coordinates, r, y and daylight reflectance Y corresponding to this Munsell notation from figures 2 to 8 in the paper by Kelly, Gibson, and Nickerson [30]. From these values, determine the Munsell renotation from figures 1 to 9 of the paper by Newhall, Nickerson, and Judd [42].

6.1.4. The Color Designation. After the Munsell notation for the sample has been determined, select the color-name chart referring to the Munsell hue of the sample (see Munsell hue designation near the upper right hand corner of the color-name chart). Plot the value and chroma of the sample on this chart and record the name of the block in which this point falls as the color designation of the sample. If, however, the point falls on a hue, value, or chroma boundary, the names of all of the blocks touching the point apply to the sample. Any one, two or all of the names may be used as the designation of the sample depending on the type of name desired.

Different degrees of precision of designation are possible under this system. For more precise designation than is possible by color names alone, specification by the Munsell notation itself can be used. For the colors of solids, powders and some colored liquids or glasses, the complete color designations (hue name and modifiers) defined herein should be used. For the colors of microscopic structures, most liquids and most chemical tests, the hue names alone are sufficient. Where two or more hue names are used, they should be arranged in sequence according to the Munsell hue sequence (red-yellowgreen-blue-purple-red).

6.1.5. An Example. Suppose that the hue of the sample falls between the 7.5YR and 10YR charts and that its value falls between the 7 and 8 value levels, but nearer the 7, and is estimated as 7.2. Suppose further that its chroma is found to be

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 interchange the positions of the charts and check the Munsell notation. If these are found to be unchanged, 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 samples 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 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 illumination 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.

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 Munsell 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 prescribed angles of illumination and viewing. The 1 and 2 above, giving particular attention to 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 brush-marked paint films may be considered as Elements. Samples of satin-finish textiles and glossy 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 obtained. Some textiles require more than one most characteristic color of the sample is usually angle of view or illumination to bring out the characteristic color or colors; changeable silks are extreme examples of such textiles.

6.3 Liquids and Nonpowdered Solids

6.3.1. Opaque Solids and Liquids. The color designation of a precipitate can be obtained in the test tube if the liquid in which it is suspended is itself not strongly colored, otherwise on a filter paper; the hue notation is usually sufficient. Opaque liquids should be placed in a clear glass vial, test tube, or bottle, and the Munsell notation of the color obtained by holding it above the charts as for opaque solids (section 6.2.1).

6.3.2. Clear Liquids. To obtain the Munsell notation of the color of a clear liquid, put it in a clear glass vial with a flat bottom to a depth of 1 cm (bottom of the meniscus); place the vial in the holder (figs. 5 and 7) which has a rectangular opening in the bottom and hold it about 8 inches above the white shield illuminated by natural or artificial daylight. Look down through the liquid at the rectangular

opening (fig. 8) and compare this color with those of the proper Munsell charts under the shield. By moving the shield around and exposing successive pairs of Munsell standards, the comparisons required in section 6.1.3 for obtaining the Munsell notation are made. The color designation is obtained from the color-name charts as before.

If only the hue name of the liquid is desired, it may be determined by holding the test tube, beaker or vial containing the liquid above the white shield as in 6.2.1 above. Certain changes must be made in the regular color names to adapt them to the description of the colors of nonopaque media. These consist of making the substitutions shown in table 2. TABLE 2. Color designations for opaque and clear samples

6.3.3. Clear Solids (Crystals, Glasses, Resins). The color designations of clear solids may be obtained if the faces of the sample are nearly parallel, smooth, and free from dust or scum. Estimate the hue notation of the color of the sample when held over the white shield as in section 6.3.2. If the size of the crystals is less than 1 mm, proceed as for an opaque powder as in 6.1. If the full color designation is desired, it may be obtained as in 6.3.2.

6.3.4. Cloudy Solids or Liquids. Sometimes the color designations of cloudy samples, that is, samples which both transmit some light and reflect some, can be obtained by transmitted light (6.3.3) but usually they are more easily specified by reflected light like opaque samples as in 6.2.

FIGURE 8. Method of using vial holder.

Munsell charts of the proper hues are placed under the shield so that the standards corresponding in value and chroma appear in the rectangular openings.

6.3.5. Fluorescent Solids or Liquids. The color of the fluorescence of a solid or liquid is determined by holding it or the test tube or vial directly in front of a vertical black velvet cloth so that the sample is illuminated by natural or artificial daylight chiefly in directions perpendicular to the line of sight. Any light incident upon the sample from the back should be avoided because it will produce a mixture of fluorescence and body colors in unknown proportions. The fluorescence color will appear the strongest on the side toward the light source. The Munsell charts should receive light from the same source and should be held slightly tilted beside the sample to facilitate the comparison. The hue notation is sufficient.

6.4. Microscopic Specimens

6.4.1. Mounting. Unless otherwise specified, the sample whether powdered or sectional is to be mounted in a colorless medium such as water.

6.4.2. Lighting. A frosted Mazda lamp is used for illumination and is placed above and to one side of the microscope base where it will illuminate both the substage mirror of the microscope and the Munsell charts (figs. 9 and 10). The proper daylight filter (blue glass) for the light-source used must be placed in the eyepiece of the comparison ocular or the Abbé-type camera lucida, whichever is used.

6.4.3. Determination of Munsell Notation. When using a comparison ocular (fig. 9), place one end over the ocular of the microscope and support the other end by a condenser clamp. If an Abbé-type camera lucida is used (fig. 10), it must be modified some what to give a split field. To do this, cut out

of a circular piece of tin foil just large enough to slip into the ocular tube of the microscope, a semicircle as shown in the accompanying diagram (fig. 11). This shield is placed on top of the ocular micrometer with the cut edge extending from back to front and constituting the dividing line. Next, place a piece of black velvet or cloth on the table beneath the reflecting mirror of the camera lucida so that its outer edge coincides with the vertical edge of the shield in the ocular tube. This cloth must cover everything on the table visible in the upper half of the reflecting mirror. the reflecting mirror. Slip an envelope of black paper or cloth down over the top half of the reflecting mirror until its lower edge also coincides with the dividing line.

Now place a mount consisting of a slide, a sample (for instance a thin section), a coverglass and liquid

FIGURE 9. Microscope and comparison ocular. The Munsell charts are placed on the table under the open end of the ocular.

D

FIGURE 11. Tinfoil cut to block out half of microscope field when placed on the ocular micrometer.