If you are using standard non-glare glass or Plexiglas,
get as little space between the actual artwork and the glass
as possible. You can also make the next step up to Den
glass or museum glass. Den glass is a copyrighted name
for a manufacturer of high-end non-glare glass. It is also
called museum glass because this is the quality of glass you
find in front of paintings at a museum.
This glass has a polarization effect put on it.
Much like the polarized filter on a photo camera it turns the
passing light at an oblique angle and eliminates most glare.
When you're facing artwork behind museum glass
you should feel you have to reach out and touch the
glass to make sure it's actually there. Museum glass
can be expensive, a 24' x 30' inch piece can be close to
$500. It is recommended for artwork of significant value,
money or otherwise.
The one issue with museum glass at the present is, if
you are standing at an oblique angle from the painting, you
will see a bluish light reflected on the glass, this is a result of
the polarized effect from the glass.
When the time comes to change your glass (either
you want to upgrade it or replace a worn and torn piece, or
your glass chipped and you did the smart thing by deciding
to change it right away) make sure you use a
professional framer to replace your glass. Do not try
to change this yourself regardless of how handy you are;
you will find trapped dust particles between the glass
and your artwork. Framers use extensive techniques to
make sure this does not happen and they do it practically for
free, especially if you buy the glass from them. If a framer
is really charging you top dollar to change out your
glass think about changing out your framer.