georgemw@speakeasy.net wrote :
On 30 Oct 2001, at 14:51, Sandy Sandfort wrote:
Mike [mmotyka@lsil.com] wrote:
I would bet that there is SOMETHING that is dissolved by liquid freon. Just mark your letters with the stuff and look for the integrity of the mark at the other end.
Or... is there something that REACTS to freon in an interesting way...?
S a n d y
I think freon is incredibly inert, that's why it's used.
Since there are so many ways to protect the contents of the message the freon topic is not all that interesting. It would be mildly amusing if there were a way to detect that freon had been used on a piece of paper. I would guess that it could be done by either finding an "ink" that was dissolved by freon or some other material that would sit happily in place until lifted and dispersed. http://solvdb.ncms.org/syn01.htm a fun solvents database - not too useful here http://www.redwop.com/technotes.asp?ID=107 not really relevant but interesting Freon seems to be ( or have been ) used mostly for degreasing. Could you make some sort of nondrying oil-based marker that would blur or weaken when drenched with freon? Probably. Buy some raw artist's pigment and mill it with a non-drying grease that is too thick to migrate appreciably over the time period of interest when applied to paper. Wetting with solvent would probably cause damage to a mark. Mike
My impression is that virtually any transparent liquid will do a reasonable job of making the envelope transparent, but the considerations are that you'd want something that doesn't leave a residue and won'tr make the ink run.
I believe that paper is white for the reason that snow is (as opposed to the reason that titanium oxide is), that is, you've got a bunch of surfaces where the index of refraction changes significantly from that of air and there's a chance of reflection at each surface, but the actual paper fibers are transparent. The liquid you spray on is filling in the gaps with something with an index of refraction much closer to that of the paper fibers.
Pretty sure that's more or less how they work. Definately there's no chemical reaction going on.
Sounds like a good explanation.
George
At 06:05 PM 10/30/01 -0800, mmotyka@lsil.com wrote:
georgemw@speakeasy.net wrote :
I think freon is incredibly inert, that's why it's used.
Since there are so many ways to protect the contents of the message the freon topic is not all that interesting. It would be mildly amusing if there were a way to detect that freon had been used on a piece of paper. I would guess that it could be done by either finding an "ink" that was dissolved by freon or some other material that would sit happily in place until lifted and dispersed.
http://solvdb.ncms.org/syn01.htm a fun solvents database - not too useful here
http://www.redwop.com/technotes.asp?ID=107 not really relevant but interesting
Freon seems to be ( or have been ) used mostly for degreasing.
It was, now it is being phased out because freon is damaging to the ozone layer. Try locating some R-12 for your automotive a/c system, time was you could buy little 12 oz bottles in do-it-yourself kits at every corner parts store. Reese
S a n d y W r o t e:
Mike [mmotyka@lsil.com] wrote:
I would bet that there is SOMETHING that is dissolved by liquid freon. Just mark your letters with the stuff and look for the integrity of the mark at the other end.
Or... is there something that REACTS to freon in an interesting way...?
IIRC in 'The Codebreakers' Kahn states that invisible ink can always be read by exposing the paper to iodine vapor, since the 'ink' distorts the fibers of the paper. Even plain water can be used to write messages. This can be defeated by wiping the surface of the paper with a damp sponge, requiring Mallory to find the correct chemical to react with the ink and cause a color change. However, _this_ can be detected by the smear left on the fibers of the paper. Perhaps this also occurs with sprayed on solvents? This could work on 'unprepared' mail. As an added bonus, the iodine vapor is _supposed_ to fade out afterwards, unless you use too much of it as we did in science class trying to develop fingerprints. The Baker Street Irregulars
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