Page:NBS Circular 553.djvu/19

 6.2.6. Metallic Surfaces. The characteristic color of a metallic surface is obtained from the specularly reflected light. Proceed, therefore, as in 1 and 2 above, but obtain, in addition, the hue name for the specularly reflected light. These two names may possibly yield a useful designation of the color of the metallic surface, but they will not correspond well with common usage which involves color terms that apply characteristically to metallic appearance, such as silver, brass, gold, copper and so on.

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 ] cm (bottom of the meniscus) ; place the vial in the holder (figs. 5 and 7) which has a rectangular opening in the bot tom 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.

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 lie obtained by transmitted light (6.3.3) but usually they are more easily specified by reflected light like opaque samples as in 6.2. 8