[Illustration: Ruling Patterns]

The geometric lathe is a most delicate and complicated machine. By means
of elaborate attachments very involved and eccentric motions are given
to the plate under the graving point and extremely complicated and
beautiful designs are produced. I think we are all familiar with these
from the examples on our national currency. Geometric lathework was used
on a number of the United States stamps of the issue of 1861 and also on
the $5,000 revenue stamp. The work of this machine is regarded as a
great safeguard against counterfeiting. The most skillful engraver would
have difficulty in imitating the simplest designs produced by it. The
machines are too expensive to be obtained by anyone but a government or
a great banknote company and there are very few men who thoroughly
understand operating them. A turn of a screw or a variation of a single
cog will change the result entirely. Finally the work of the lathe is
often reversed, so that the line which is cut by the graver and should
print in color prints white, and vice versa. It would not be possible to
imitate this by hand engraving.

Printing from line-engraved plates is largely done by hand presses. The
ink used is very thick. When black it is made of finely pulverized
carbon, mixed with oil. Colored inks are composed of zinc white and dry
colors, ground in oil. The colors are animal, vegetable or mineral. The
latter cause the plates to wear out rapidly. Green is an especially
destructive color. In recent years aniline colors have been largely
employed. They afford an elaborate range of shades and color
combinations which are most puzzling to describe. Soluble inks are much
used by the leading English firm of stamp printers. They are very
sensitive to water and are regarded as one of the best preventatives of
the cleaning of used stamps. Beautiful results are obtained by printing