By a little gentle friction with a wet sponge, the
development will be materially promoted.
A highly interesting peculiarity of this anthrakotype process is the
fact that a copy, though it may have been incorrectly exposed, can
still be saved. For instance, if the image does not seem to be vigorous
enough, it can be intensified in the simplest way; it is only necessary
to soak the paper afresh, then dust on more color, etc.; in short,
repeat the developing process as above described. In difficult cases the
dusting-on may be repeated five or six times, till at last the desired
intensity is obtained.
By this process, therefore, we get a positive copy of a positive
original in black lines on a white ground. Of course, any other coloring
material in a state of powder may be used instead of soot, and then a
colored drawing on a white ground is obtained. Very pretty variations of
the process may be made by using gold or silver paper, and dusting-on
with different colors; or a picture may be taken in gold bronze powder
on a white ground. In this way colored drawings may be taken on a gold
or a silver ground, and very bright photo tracings will be the result.
Some examples of this kind, that have been sent us from Vienna, are
exceedingly beautiful.
Summing up the respective advantages of the two processes we have above
described, we may say that "nigrography" is best adapted for
copying drawings of a large size; the copies can with difficulty be
distinguished from good autographs, and they do not possess the bad
quality of gelatine papers--the tendency to roll up and crack.
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