A watermark is a design "embedded"
in a sheet of paper and may be found on fine paper stock available at most stationers,
stock used to make currency and banknotes, and for our purposes,
on certain postage stamps. A watermark can depict almost
any design, but the U.S. chose to use only three letters, "U",
"S", and "P",
to make all the watermarks on its postage stamps, although it
did accidentally use the letters "I" and "R"
on three of its regularly issued stamps,
Paper is made by allowing a thin layer of paper pulp to dry over
a wire mesh. Early watermarks on hand-made paper were made by either raising the wire mesh in the area of the
desired design or more often by attaching an additional thin wire mesh shaped in the design of the
watermark. This effectively made the paper in the area
of the watermark thinner than the surrounding paper and standout when held to a bright
light since it transmits light more readily. Watermarks on
hand-made paper usually stand out quite well when held to strong
With machine-made paper, from which most U.S. stamps are
printed, the process is somewhat different. The watermark is
added by applying a cylindrical device called a "dandy
roll" to the paper after the paper has already begun to
dry, resulting in watermarks that are not as pronounced and
therefore more difficult to detect. Most watermarks on U.S.
stamps will not be visible unless placed in a
dark tray with watermark fluid, The watermark appears darker
since it is thinner than the surrounding stamp and lets the
reflection from the dark tray through more readily.
The watermark design was added many times in a regular pattern to make a
single sheet of printable paper stock, the double-line in regular rows and
columns and the single-line in
an offset diagonal. The watermark pattern was
independent of the size and design of the stamp and can
therefore appear in just about any position on any given
stamp, but must always be either parallel or perpendicular to
the design of the stamp.
To get an idea of where the watermark can appear
on a stamp, cut a small rectangular window the size of the stamp
out of a small piece of cardboard and place this cutout over one
of the watermark templates. From the
cutout at right the bottom of the letter "S", the top
right of the letter "P" and the top left of the letter
"S" will be on the stamp. It is fairly easy to verify
that on a normal-sized Washington-Franklin stamp, at most three
letters are possible on a single-line watermarked stamp and four
letters on the double-line watermarked stamps.
Watermarked "Error" Stamps
There were three regularly issued U.S. postage stamp inadvertently printed on
the Internal Revenue "USIR" watermarked paper. The 6c
and 8c First Bureaus (Triangles), Scott 271a and 272a, were
accidentally printed on this stock. They must have either a clear "I" or a clear
"R" to be certified genuine since the "U" and the "S" of
the "USIR" watermark are for practical purposes indistinguishable from the
"U" and the "S" of the double-line "USPS"
watermark. On the other watermark error, the $1 Wilson Prexie,
Scott 832b, any watermark including the "U"
and the "S", will confirm the error since the
regularly issued stamp was was not printed on
It is important to note that watermarks are sometimes faked to
"create" the more expensive counterpart and sometimes
to hide a thin. Knowing where the watermark can and cannot
appear may help to catch this problem. The fake watermark is
made by scraping away some of the stamp paper in the shape of a
watermark, creating a thinned area on the stamp. Thins can be
distinguished from genuine watermarks by the way the stamp dries
after having been submersed in fluid. A thin will "whiten out", a
genuine watermark will not. This scraping method will not work
with genuinely gummed stamps, since the scraped area will be
obvious. However, it is possible to remove the gum, scrape the
stamp in the pattern of a watermark and then regum the stamp.
Again the stamp will "whiten out" in the area of the