In the case of the 506 process, the sample shade of
the grain surface is gray (Fig. 1a and c) with outlined boundaries of
grains with the settled carbon deposit (Fig.1c), in the background of
which one can also observe a small number of brighter areas
(Fig. 1a). In the scanning microscope photographs these are shown
as darker areas (Fig. 1c). The shade of the grain surface for the 505
process sample differs from the sample 506, which is especially
visible in the photograph taken with the scanning microscope
(Fig. 1d). The photograph presents grains with a gray shade and
grains with a mixture of gray and dark areas (Fig. 1d) In the
photograph taken with the optical microscope (Fig. 1b) the dark
spots correspond to the dark areas in the scanning microscope
photograph.