In forgeries perpetrated by the aid of tracing, the internal evidence is more or less conclusive according to the skill of the forger.  In the perpetration of a forgery the mind, instead of being occupied in the usual function of supplying matter to be recorded, devotes its special attention to superintendence of the hand, directing its movements, so that the hand no longer glides naturally and automatically over the paper, but moves slowly with a halting, vacillating motion, as the eye passes to and from the copy to the pen, moving under the specific control of the will.  Evidence of such a forgery is manifest in the formal, broken, nervous lines, the uneven flow of the ink, and the often retouched lines and shades.  These evidences are unmistakable when studied with the aid of a microscope.  Also, further evidence is adduced by a careful comparison of the disputed writing, noting the pen-pressure or absence of any of the delicate unconscious forms, relations, shades, etc., characteristic of the standard writing.

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.