Transperancy Spray?

mmotyka at lsil.com mmotyka at lsil.com
Tue Oct 30 18:05:38 PST 2001


georgemw at speakeasy.net wrote :
>On 30 Oct 2001, at 14:51, Sandy Sandfort wrote:
>
>> Mike [mmotyka at 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  





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