Forgeries by tracings usually present a close resemblance in general
form to the genuine, and are therefore most sure to deceive the
unfamiliar or casual observer. It sometimes happens that the original
writing from which the tracings were made is discovered, in which case
the closely duplicated forms will be positive evidence of forgery. The
degree to which one signature of writing duplicates another may be
readily seen by placing one over the other, and holding them to a
window or other strong light, or by close comparative measurements.

Traced forgeries, however, are not, as is usually supposed,
necessarily exact duplicates of their originals, since it is very easy
to move the paper by accident or design while the tracing is being
made, or while making the transfer copy from it; so that while it
serves as a guide to the general features of the original, it will
not, when tested, be an exact duplication. The danger of an exact
duplication is quite generally understood by persons having any
knowledge of forgery, and is therefore avoided. Another difficulty is
that the very delicate features of the original writing are more or
less obscured by the opaqueness of two sheets of paper, and are
therefore changed or omitted from the forged simulation, and their
absence is usually supplied, through force of habit, by equally
delicate unconscious characteristics from the writing of the forger.
Again, the forger rarely possesses the requisite skill to exactly
reproduce his tracing. Much of the minutiae of the original writing is
more or less microscopic, and from that reason passes unobserved by
the forger. Outlines of writing to be forged are sometimes simply
drawn with a pencil, and then worked up in ink. Such outlines will not
usually furnish so good an imitation as to form, since they depend
wholly upon the imitative skill of the forger.