Anti copy coating

Has anyone developed a coating for paper which will make it impossible to copy using xerography?
I have in mind some sort of florescent coating which would make the copy
either all white or all black. And it should only be initiated if the light level exceeds a certain treshhold, like in a photocopy machine.
I imagine it would also have to flouresce at different wavelengths to be universal, or close to it, to the varieties of illumination available on these machines.
An application would be on currency so it could not be copied by kiddies looking to enrich themselves.
Al
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Al wrote:

You are looking for the holy grail of document security. There really is not enough "blue" or UV light in most scanned light bars to give any reasonable fluorescence. The newer iamge bars in MFP's will not be any easier to defeat. Try your question in one of the comp.printers newsgroups.
Mike
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His specification is incomplete. Black India Ink satisfies OPs original specification. Coating documents with Black India Ink will make them impossible to copy using xerography.
What he wants is a bit harder, something that will make copying impossible while allowing visual examination by humans. So, one asks is there any major differences in the optical sensitities of human eyes and copy machines photoconductive drums -- and can such be exploited to achieve UNcopiability whilst retaining readability.
The answers are, of course there are differences. And, to date, no one has found exploits which reliably achieve readability and UNcopiability simultaneously.
I suspect studying optical illusions to design printing methods that produce this effect may be a more fruitful endeavor in the short term.
In the long term, just remember it is useless to attempt a technological fix for a social problem. At best one can find technological aids to social fixes to social problems.
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Thank you for the clarification.
And thanks to all who responded.
I have found that using a light blue ball point ink on a light blue background works the best so far. The eye can see the image, but the photocopier cannot produce enought contrast for a good image.
I suppose this is a Holy Grail type quest, but I'm sure someone will find a way.
Al
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Its probably a lot cheaper and easier to have a latent image foil the copy...
http://www.highsecuritypaper.com/features--hiddenmessage.html
Regards, R. David Zopf Bomar Specialties Co. www.bomarspecialties.com
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Al wrote:

Yes, I saw a piece of such a sheet many years ago. A classmate of mine had a father who worked with classified information, and my classmate showed me a fragment of a sheet of paper which he said was specifically designed to be difficult to xerox.
The paper was deep orange in color. I don't think it had any fluorescent properties -- it merely reflected light at a wavelength to which the selenium glass drum had poor sensitivity.
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Mark Thorson wrote:

It has been many years since selenium was used on a photpreceptor drum. Nowdays all copiers are MFP's and have red/near infrared sensitive drums.
Mike
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BSI used to produce some British Standards on orange paper to make them difficult to photocopy. But it wont stop scanning, photographing etc.
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Our labs came up with an excellent solution to this problem. Black print on black paper of the exact same shade... Photocopies of the document will be unreadable.
Hey, it works...
If the goal is trying to prevent quick and easy copying, what about making the documents in such a fashion that they have to be read under a specific frequency of light that isn't readily available? I.e. a sophisticated version of invisible ink? Besides preventing photocopying, I wonder if there's a type of light that would be both not hard on the eyes and also doesn't photograph well without special measures?
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Wiseguy wrote:

That would not be secure against someone slipping a sheet of a filter material between the paper and the platen.
Better would be a fluorescent pigment or dye that had an absorption band well outside of the range of any copier or scanner light source. Even better would be a selection of such pigments to make interfering patterns, so that you'd need a bandpass filter to view only the desired pigment.
Which reminds me of a form of vandalism I had thought of. With the right selection of colors to make interfering patterns, it would be possible to spray-paint obscenities (or whatever) such that only people with certain forms of color blindness would be able to see them.
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