I've been trying to come up with a list
of characteristics to help distinguish a genuine 6c from a forgery.
But there hasn't been, at least to my knowledge, a problem with
forgeries for this issue. The modern day photographic forgeries
on thin paper are about the only ones that might fool someone,
and only because they are replicas of genuine stamps.
The one detail that seems to be lacking in all the forgeries
I've seen is this:
The background mesh is comprised of horizontal and
vertical crossed lines. There is a thin white gutter between
the central area of corssed lines and the outer frame. Some of
these crossed lines that form the background mesh extend beyond
the confines of the central area into the thin white gutter (detail).
There are some extended lines that are consistant on each and
every position in the plate, such as the 2 lines just under the
numeral 6 in the top inscription (detail) and others are unique to particular
positions. Some are not as distinct as others, but every 6c will
have some. The modern forgeries also show some of these lines,
but they are not as distinct.
There is also a small "knob" of black color
in the upper left corner of the central design area, that protrudes
into the thin white gutter (detail). It seems to be missing on most forgeries,
with the exception of the photographically produced replicas
of modern times.
This is one of the more decieving forgeries.
It is attributed to Miguel Segui, in the early part of the 20th
Segui's forgeries have a certain "look"
to them, that makes them pretty recognizable, if you've seen
enough of them. The colors are usually pasty looking, the impression
is rather flat, and shading lines that should be fine are usually
thick and coarse (comparative
detail), and this forgery is no exception.
Although it does retain most of the general characteristics
of a genuine stamp, due to the fact that it is a photographic
copy of the real thing, it is lacking in fineness. Notice that
the black "knob" of color is present in the upper left
corner of the background mesh, but it lacks any of the fine lines
that extend into the white gutter area.
Most of the segui forgeries I've seen are in unused
condition, without gum, and seem to find there way into collections
more than others. I've had more than one person ask me to look
at unused Spanish stamps, from a valuable collection,
only to find that they are Segui products.