oxide is usually the best compound for polishing glass.
Glass has a hardness of slightly less than 6 in Moh's
scale of hardness and will scratch most soft minerals.
However, minerals with a hardness of 6 or more will easily
scratch a piece of glass. Before you begin polishing a
piece of glass you must first determine how deep the scratches
are in the material. First run your fingernail across
the item to be polished. If you can feel the scratch,
it may be too deep to be polished out with cerium oxide
and may require more aggressive grinding.
grit size used to grind out a scratch always depends on
the depth of the scratch to be polished. Starting with
a fine 1,200 grit size would be best. However, this may
be slow. If this is the case you can start with a coarser
600 grit then move to the 1,200 or a 3,000 grit to remove
the scratches from the coarser grit size. You can now
proceed to polish the glass with cerium oxide. Another
great way to grind out the scratches from glass is to
use a diamond powder with oil as a lubricant.
each grinding, clean the area you have ground with alcohol
before going to the next finer grit size. Each grit should
be used on a clean polishing pad. An electric buffer or
drill works best if the item is not too delicate. Mix
cerium oxide with water to create a slurry. Apply the
slurry to a felt buffing pad. Harder buffing pads made
out of hard felt, or leather work best.
polishing action will go faster when the cerium oxide
is damp, but not dry or too runny. You can use a spray
bottle with water to keep the area you are polishing damp.
You can use 99.9% cerium oxcide. However, it can be a
bit more expensive than the 90% Optical grade which will
work fine on most glass.
Moh's Hardness Scale
Hardness is measured on the Moh's Scale,
identified numerically hardness of by standard minerals,
from 1 (softest) to 10 (hardest):
A mineral of a given hardness will scratch other mineral
of a lower number. With a systematic approach, you can
use minerals of known hardness to determine the relative
hardness of any other mineral.