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.
6.4.1. 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. 
Figure 9. Microscope and comparison ocular.
The Munsell charts are placed on the table under the open end of the ocular.
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 Abbe-type
camera lucida is used (fig. 10), it must be modified
somewhat 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. 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. 
Figure 10. Microscope and modified Abbe-type camera lucida , showing position of black velvet used to block out one-half of the comparison field and one-half of the inclined mirror.
Figure 11. Tinfoil cut to block out half of microscope field when placed on the ocular micrometer.
Now place a mount consisting of a slide, a sample (for instance a thin section), a coverglass and liquid
