inks
in the same paper or document is very likely to be erroneous for the
reason that when a lighter ink is more heavily massed than a darker
one the effect on the eye is as if it were the darker. Under a
microscope or magnifying glass the field is more restricted, the finer
lines are broadened, and one has larger areas of ink to compare with
less surface of strongly contrasted white paper. Then, again, an ink
without noticeable bluish tinge to the naked eye may appear quite blue
under the glass where the films of ink are broadened and thinned and
their characters better observed.

In order to judge whether two marks have been made by the same ink,
they should be viewed by reflected light to note the color, luster and
thickness of the ink film. Many inks blot or "run" on badly sized
paper--i.e., the lines are accompanied by a paler border which
renders their edges less well defined.

Even on well-sized papers this class of inks usually exhibits only a
stained line of no appreciable thickness where the fluid has touched
the paper.

The copying and glossy inks, which often contain a considerable
quantity of gum, do not "run" or blot even on partially sized paper,
and show under the glass a convexity on the surface of the line and an
appreciable thickness of the film.

It does not always follow when an ink has made a blur on one part of
the paper and not on another that the paper has been tampered with. A
drop of water accidentally let fall on the blank page will frequently
affect the sizing in that place, and, besides, all papers are not
evenly sized in every part.

The inks rich in gum, or those concentrated by evaporation from
standing in an open inkstand, give a more lustrous and thicker stroke.
Some inks penetrate deeper into the paper than others, and some
produce chemical effects upon the sizing and even upon the paper
itself, so that the characters can easily be recognized on the
underside of the sheet. In some old documents the ink has been known
to so far destroy the fiber of the paper that a slight agitation of
the sheet would shake out as dust much of the part which it covered,
thus leaving an imperfect stencil plate of the original writing.

Distilled water is very useful in many cases to ascertain whether
paper has been scratched and partially sized or treated with resin. If
it has not been altered by chemical agents, the partial sizing and the
resinous matter used give to the paper a peculiar appear