254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
good whites, but should never be intensified twice, as otherwise the 
first lamina will be converted into an opaque mirrorlike film, and 
therefore the chromatic interference which is specially produced by 
the second lamina can not longer take place. 
ANALYSIS OF OVEREXPOSED PLATES. 
Even by mere examination an overexposed picture shows a luster- 
less white, grayish or pinky, and more or less pure, but hard-silhou- 
etted colors. Microscopic analysis explains this phenomenon, which 
is one of the most frequent defects in working Lippmann’s process. 
The lamine of such plates consist of a thin yellowish and extraor- 
dinarily pale precipitate, which allows more light to pass to the 
underlying films than usual. The intervals also are more or less 
strongly acted upon; they show a delicate, hght gray grain forma- 
tion, so that the contrast between the laminz and intervals is con- 
siderably decreased (fig. 13). Finally, the first lamina is completely 
wanting or reduced to a pale indefinite stripe (figs. 12 and 13). This 
paleness is more or less seen in the second lamina. The phenomenon 
naturally depends on the fatigue of the surface region of the sensi- 
tive film, which is so strongly solarized that it can not be reduced to a 
dark color. 
Whites show in overexposed plates a very pale and transparent 
mirror film, which with considerable solarization may even be totally 
absent. The pale, small, yellowish and almost invisible grains possess 
no reflective power. Behind the mirror zone are various fine stripes 
without contrast, and an extended region of irregular and compara- 
tively vigorous reduction which extends to the glass. 
CHANGE OF COLOR BY OVERDEVELOPMENT INTENSIFICATION. 
The least overstepping of the correct exposure leads, as will be seen 
later, to falsification of the colors and loss of the whites. Red and 
orange are exceptions, the two colors which from their poor photo- 
chemical action rather gain than lose with moderate overexposure. 
The color value of the picture is also changed by overdevelop- 
ment or intensification, even if the plates are correctly or slightly 
underexposed. If the damage is not too great it can be equalized by 
cementing under a prism with Canada balsam, as then the gelatin 
loses a little water, and therefore the lamine get nearer one another. 
If the fault exceeds certain limits, the colors are so falsified that 
neither in moderately oblique hght nor in a benzole tank will the 
picture give the true colors. 
Microscopic analysis shows that such color changes are to be 
ascribed to a thickening of the first lamina, which then reaches the 
surface of the gelatin. Since by this thickening the difference in 
