9.8.
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317
The novice may wonder what is meant by a full development. The
process of paper development has four rather well-marked stages which
are easily recognized. There is first a considerable time interval after an
exposed piece of paper has been put in the developer when nothing seems
to be happening. Then, suddenly, an image begins to appear, and darkening of the major blacks occurs rapidly until the principal features of
the picture are evident. There are not good tonal gradations, however,
until toward the end of this phase as the development completes itself.
During this time, development slows down so that the novice may think
it is finished before it really is, and so he may remove the picture from the
developer too soon. There is no danger in leaving a properly exposed
print in the developer for much longer, however, for the third period is
once again a time when nothing seems to happen. The fully developed
picture can stay in the developer for 5 min or more before finally fogging
starts, and all parts of the picture begin to darken. One should be sure
that each picture reaches that plateau of inactivity which indicates full
development if he wishes the maximum range of tonal values.
The beginner is apt to misjudge his printing in two respects. A wet
print in a developing tray being observed with a safelight looks very much
darker than it finally will appear to be. One has to learn to take this deception into account, and let prints become very dark looking indeed in
the developer before fixing them. The beginner is also apt not to realize
or to forget that pure white areas on a finished print perhaps should have
had pale detail in them. Thus, if the print is underexposed, detail which
was present in the negative may not be seen at all in the print. Professional
photographers have a well-founded rule that there should be no pure
whites in a print. This is an excellent rule for electron microscopists.
One should always expose so that at least a little gray tone appears in the
lightest part of the print. This ordinarily can be seen appearing in contrast
to the pure white edges that have been masked. It is only in this way
that one can be sure to cover the full range of tonal values that are present
FIG. 38. (a) A properly exposed and fully developed print of glomerular capillary
loops of a rat kidney, showing particularly an epithelial cell in the urinary space,
(b) The same negative printed on an identical grade of paper, but "pulled." The
negative was deliberately much overexposed and underdeveloped. Although the background contrast is much the same in the two pictures, the incorrectly printed one lacks
tonal range.
Tissue fixed in osmium tetroxide, embedded in methacrylate, stained with phosphotungstic acid, and sandwiched.
ENLARGING
317
The novice may wonder what is meant by a full development. The
process of paper development has four rather well-marked stages which
are easily recognized. There is first a considerable time interval after an
exposed piece of paper has been put in the developer when nothing seems
to be happening. Then, suddenly, an image begins to appear, and darkening of the major blacks occurs rapidly until the principal features of
the picture are evident. There are not good tonal gradations, however,
until toward the end of this phase as the development completes itself.
During this time, development slows down so that the novice may think
it is finished before it really is, and so he may remove the picture from the
developer too soon. There is no danger in leaving a properly exposed
print in the developer for much longer, however, for the third period is
once again a time when nothing seems to happen. The fully developed
picture can stay in the developer for 5 min or more before finally fogging
starts, and all parts of the picture begin to darken. One should be sure
that each picture reaches that plateau of inactivity which indicates full
development if he wishes the maximum range of tonal values.
The beginner is apt to misjudge his printing in two respects. A wet
print in a developing tray being observed with a safelight looks very much
darker than it finally will appear to be. One has to learn to take this deception into account, and let prints become very dark looking indeed in
the developer before fixing them. The beginner is also apt not to realize
or to forget that pure white areas on a finished print perhaps should have
had pale detail in them. Thus, if the print is underexposed, detail which
was present in the negative may not be seen at all in the print. Professional
photographers have a well-founded rule that there should be no pure
whites in a print. This is an excellent rule for electron microscopists.
One should always expose so that at least a little gray tone appears in the
lightest part of the print. This ordinarily can be seen appearing in contrast
to the pure white edges that have been masked. It is only in this way
that one can be sure to cover the full range of tonal values that are present
FIG. 38. (a) A properly exposed and fully developed print of glomerular capillary
loops of a rat kidney, showing particularly an epithelial cell in the urinary space,
(b) The same negative printed on an identical grade of paper, but "pulled." The
negative was deliberately much overexposed and underdeveloped. Although the background contrast is much the same in the two pictures, the incorrectly printed one lacks
tonal range.
Tissue fixed in osmium tetroxide, embedded in methacrylate, stained with phosphotungstic acid, and sandwiched.