We have
all seen glass pitted like the headlight below, or maybe
something even more common like a scratch on a windshield.
This kind of wear is typical on glass of any age, but is easy
to fix with the correct tools. The first step in addressing
surface issues on glass is to determine the extent of the damage.
If the glass is cracked this guide will not help you.
If the glass is not cracked and the flaw cannot be felt with
your finger, then you can skip the sanding step and go right to
polishing.
For
something like the headlight above or any deep scratch start with sand
paper. The correct grit depends on the depth of the pits or
scratch. Start with the finest grit that will remove the
amount of material that is needed. I do not suggest going
below 600 grit for simple scratch removal. All glass sanding
should be done wet. Add 2-3 drops of dish soap to an ounce of
water. Regularly wet your sand paper in the soap
solution. In the image below you can see what the glass will
look like both polished and sanded. Even after sanding with
2000 grit the glass will have a dull finish to it.
For the
final polish I have only found one product that works well.
Cerium oxide will make quick work out of polishing any glass.
Diamond powder also works but will not provide the new look
that cerium will. Any glass shop or larger hobby shops that
sell telescopes can provide you with cerium oxide. Depending
on the quality expect to pay about 3-7 dollars an ounce. One
ounce will go a long way and is easily enough to polish a very badly
pitted headlight. I mix the powder 2:1 by volume with water in a plastic lid. This will make a paste for easy
application to the felt wheel.
Mixed, the
cerium should be about the consistency of rubbing compound.
Apply the mixture to a high speed wheel and begin applying
using moderate force. As the mix dries apply more water as
need with a spray bottle. Periodically wash the piece and see
how it is progressing. If you still have pits or a scratch,
it may be necessary to repeat the sanding process.
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