Newspaper and Cleaning Glass

name         Chris
status       student
grade        9-12
location     CA

Question -   Why are newspapers very effective in cleaning 
glasses/mirrors? Why does the ink from newspapers not stain the 
glasses/mirrors?
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    Some newspapers will cause glasses and mirrors to smear. There 
 are several factors that play a role:
1. Newspaper (in the trade referred to as "newsprint") contains no 
solid components like calcium carbonate or silica, like higher 
quality paper. These minerals can scratch the glass, which can be 
confused with smearing.
2. Older newspapers were printed (and many still are) with oil based inks --
basically a cheap mineral oil. These too will smear or stain a 
window or mirror if a solvent or detergent is used to "clean" the surface.
3. Now the trend in printing inks for newspapers is to use water 
based inks. This allows newer and different types of pigments to be 
used too. These papers don't contain the oil of the older 
conventional inks and consequently are less likely to stain or smear 
a mirror or window.
    There are two tests to tell which type of paper/ink combination 
 is being used:
1. Hold the newspaper (or magazine for that matter) between your 
thumb and index finger for a minute or so. If your thumb/finger 
stains, you are using the old type of ink. The newer water based 
inks do not transfer on to your finger.
2. A related test is to gently rub the newspaper with a piece of 
typing paper. The friction will cause the older paper/ink 
combination to stain the typing paper. The newer water based systems 
are much more resistant to this type of test.

Vince Calder
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Chris,

Newspapers are good at cleaning glass because the paper leaves very 
little lint.  Compared to paper towels, news print is much more 
rigid and hence the fibers will not individually separate like they 
will from a paper towel.  This is the source of the lint.  The ink 
does not come off for two reasons, one you are wiping a mirror or 
glass, which is a highly polished surface, so there is nothing for 
the dried ink to stick to.  Second, upon wetting the news print with 
liquid, the ink becomes infused in the fibers of the 
newsprint.  Think of ink as nothing more than a stain. It is hard to 
stain windows with ink, yet easy to stain paper.  Glass does not 
absorb ink, while paper will.  And so all of the dirt on the window 
or mirror will be absorbed into the news print.

To think of this more on a molecular level, the paper is nothing 
more than long interlinked strands of atoms with a flexible 
backbone.  Glass however, is a highly crystalline solid that is 
hydrophobic (repels water).  The molecular properties of each give 
the unique properties in absorbing stains.

Matt Voss
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