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Invisible Ink
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stribs
science forum beginner


Joined: 12 Jul 2006
Posts: 1

PostPosted: Wed Jul 12, 2006 4:46 am    Post subject: Invisible Ink Reply with quote

I am looking for a low-cost, non-toxic solution to the following
problem:

I have some plastic cards (the material appears to be like a laminated
business card) that I would like to mark in such a way that, although
invisible under normal conditions, becomes visible in water.

I considered phenolphthalein, (using soapy water to bring out the
mark), but I question whether it would adhere well to the slick plastic
surface. Would it rub off if the card is casually handled? I guess I
need something akin to a phenolphthalein-based indelible marker!

Of course, there may be better solutions as well. If anyone has any
idea on this matter, it would be greatly appreciated.
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Ron Jones
science forum Guru Wannabe


Joined: 16 May 2005
Posts: 175

PostPosted: Wed Jul 12, 2006 6:25 pm    Post subject: Re: Invisible Ink Reply with quote

stribs wrote:
Quote:
I am looking for a low-cost, non-toxic solution to the following
problem:

I have some plastic cards (the material appears to be like a laminated
business card) that I would like to mark in such a way that, although
invisible under normal conditions, becomes visible in water.

I considered phenolphthalein, (using soapy water to bring out the
mark), but I question whether it would adhere well to the slick
plastic surface. Would it rub off if the card is casually handled?
I guess I need something akin to a phenolphthalein-based indelible
marker!

Of course, there may be better solutions as well. If anyone has any
idea on this matter, it would be greatly appreciated.

phenolphthalein won't work unless you get to pH9, the soapy water would have
to be quite strong. Why visible with water? What's wrong with a uv marker,
and a uv lamp? I would guess that not much is going to stayed stuck to the
plastic if you keep wetting it with soap.

--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near missesa at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein
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Dirk Bruere
science forum addict


Joined: 16 Feb 2006
Posts: 62

PostPosted: Wed Jul 12, 2006 8:14 pm    Post subject: Re: Invisible Ink Reply with quote

Ron Jones wrote:
Quote:
stribs wrote:
I am looking for a low-cost, non-toxic solution to the following
problem:

I have some plastic cards (the material appears to be like a laminated
business card) that I would like to mark in such a way that, although
invisible under normal conditions, becomes visible in water.

I considered phenolphthalein, (using soapy water to bring out the
mark), but I question whether it would adhere well to the slick
plastic surface. Would it rub off if the card is casually handled?
I guess I need something akin to a phenolphthalein-based indelible
marker!

Of course, there may be better solutions as well. If anyone has any
idea on this matter, it would be greatly appreciated.

phenolphthalein won't work unless you get to pH9, the soapy water would have
to be quite strong. Why visible with water? What's wrong with a uv marker,
and a uv lamp? I would guess that not much is going to stayed stuck to the
plastic if you keep wetting it with soap.


A UV lamp can just be one of those UV LEDs

Dirk
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Uncle Al
science forum Guru


Joined: 24 Mar 2005
Posts: 1226

PostPosted: Wed Jul 12, 2006 10:51 pm    Post subject: Re: Invisible Ink Reply with quote

stribs wrote:
Quote:

I am looking for a low-cost, non-toxic solution to the following
problem:

I have some plastic cards (the material appears to be like a laminated
business card) that I would like to mark in such a way that, although
invisible under normal conditions, becomes visible in water.

I considered phenolphthalein, (using soapy water to bring out the
mark), but I question whether it would adhere well to the slick plastic
surface. Would it rub off if the card is casually handled? I guess I
need something akin to a phenolphthalein-based indelible marker!

Of course, there may be better solutions as well. If anyone has any
idea on this matter, it would be greatly appreciated.

Render the surface microroughened and hydrophobic. It makes no
difference in air. Under water the entrained air layer will be
reflective like a mirror.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
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