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Name: Chris
Status: student
Grade: 9-12
Location: CA
Country: N/A
Date: September 2006

Question:
Why are newspapers very effective in cleaning glasses/mirrors? Why does the ink from newspapers not stain the glasses/mirrors?



Replies:
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


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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