>Mike, steel is softer than glass on the Moh's (?) scale.  However, rust
>is harder than glass, so if you use a used piece of steel wool, it will
>definitely scratch.  Same goes for a razor scraper blade - always use
>new on glass.

It is a fact that softer materials will abrade harder. It's just that
the harder abrades the softer more. So mild steel certainly will
scratch glass... rust is not necessary.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
<andrew.grebneff@stonebow.otago.ac.nz>
Seashell, Macintosh, VW/Toyota van nut