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 forgery is listed as the worlds first
"postal" forgery. It was made at the time that Spain's
first issue was in use in 1850. Only 1 copy exists and the perpetrators
were caught almost immediately. This forgery sold at an Afinsa
auction in 1997, with an auction estimate of. It's safe to assume
that no one will "run into" a second copy of this forgery
so I won't bother trying to pick out details that distinguish
it from a genuine stamp.
It's actually a very crude example and all you have
to do is compare it once to a genuine copy and wonder how the
forger(s) thought they could pass it off as real.
Just thought everyone would like to see it, in case
you didn't know of it's existance.