Paper watermarking security

[GtPrOjEcTX]

I'm curious on the details on this. Obviously paper can be printed so that to the naked eye there is nothing suspicious about it, however when copied or even photocopied, something may show up such as ?Copied, Not Original? or the like.

Is this a different type of ink used? Different way of printing the ink on the paper? What is happening during the process that makes this different then a normal print?

Also are there some copiers that can get by this method? If so what is being done differently?

Links to sites with such information would be helpful (I?ve googled without much luck)

 

[GtPrOjEcTX]

no?

 

[Mday]

while i do consider this somewhat off topic, but i'll answer it.

"watermarks" in the traditional sense are created before the "paper" is dried. a stamp is placed on the watery mush which decreases the thickness by a very small amount. sometimes such watermarks are visible without the use of a light. the decreased thickness allows your eye to pickup transluscence of the "paper" with a backlight.

"ink" in the traditional sense uses some sort of color in the form of a pigment or dye. usually we can see this. there are modern liquid "inks" which are invisible to the naked eye, but appear when exposed to other chemicals or "UV". the UV (ultraviolet) is the type of ink you're looking for. these chemical inks are invisible to the naked, but when exposed to UV, they "glow" or turn black or something. this depends on the type of ink used. this glowing or blacking is usually temporary, and can be made permanent. sometimes currency is also doped with some chemical which allows for those counterfeit detecting pens to work. think of it as invisible ink backwards.

now, back to the copying machine. the lights used often do emit UV, sometimes even intentially to exploit the UV inks. there is also a contrast\hue issue involved. some inks used on certain papers are not detectable by the copying machine. some colored inks which we can see appear differently under certain conditions.

what terms did you google with? "counterfeit" "ink" "currency"

 

[AbsolutDealage]

sometimes currency is also doped with some chemical which allows for those counterfeit detecting pens to work. think of it as invisible ink backwards.

Actually, the counterfeit pens work because currency is not regular paper, it is actually a cloth primarily composed of linen fibers, IIRC.