Date: Wed, 2 Aug 89 18:37:00 EDT
Subject: Re: "copy proof paper"
Defeating a "copy proof" paper based on paper color only is fairly
straightforward. You get a sheet of colored celluloid or the like and
place it in front of the item being copied. Look through the celluloid
and if you can't SEE the lettering, the copier generally won't either.
Our copier (one of the newer Xerox models) has sufficient contrast
adjustments that the quality of the copy can nevertheless be made most
adequate. The same trick can be used if you want to duplicate the
red "proof" photos some photographers use. A useful fact is that a
CuSO4 solution (copper sulphate) of reasonable density will filter
out ALL red light (down to the sub 1 photon level; it's used to
filter lasers and select second harmonic radiation!). Use a small
bit as a filter & contact print the pic onto roll film...voila!
Your very own negative! (This is a major pain in the neck to do and
should not become a habit...the poor photog. has to make a living,
after all. The filtering technique is occasionally useful though.)
Date: Sat, 12 Aug 89 20:22:00 EDT
From: Douglas James Martin <USERDJMA@UALTAMTS.BITNET>
Subject: Re: "copy proof paper" - does such a thing exist?
Light blue is also often used in some vital parts of the docs of computer
games rather than copy-protection of the disk; you can copy the game disk
fine but the game is unplayable without tedious manual copying of the
This was a long time ago, so I can't give sources, but I'm sure I read
somewhere of the use of dyes that are highly flourescent under the lights
used by copiers (something about there being lots of UV in them) used to
screw up copying.