Mike Aurelius" mike@auralens.com about: Polishing Cerium
Cerium oxide is a widely used ‘rare earth’ for polishing glass.
It comes in many varieties, the most common is tan to dark brown
(indicating high iron content). Pure cerium is white (and very
expensive). The dust, if inhaled, can lead to respiratory
problems, however, it is designed to be used wet. Any splash you
get should be cleaned up with a damp rag. There are no know
disposal problems (not considered hazardous waste).
That being said, it is important to note that the dark brown
cerium now available from some suppliers may be coming from
China and MAY be contaminated with thorium. A large optical
manufacturer just down the street found out their entire lot of
polish (and also their semi truck full of ground
glass/grinding/polish sludge) was radioactive, was impounded by
the EPA, and now have a BIG mess to clean up. Moral - enquire
of your supplier the source of the cerium, and if it has been
checked for thorium content.
As a side note, we are using the white cerium, and have found
that it lasts almost forever.
I’m new here so I didn’t read the beginning of this thread, I hope my
ramblings don’t rehash previous comments. I think the answer to your
question is it depends on how “minor” the scratches are.
A customer once successfully polished a scratched opal in its setting
with (I think it was) tin oxide, entirely by hand on a moist towel
while watching TV each evening (Jeopardy and Wheel of fortune, she
said). It took her a week and she LOVED to talk about it.
I have succeeded in polishing scuffed/scratched showcase windows –
the sort of thing that happens when some ungainly metal display item
rests against the glass while driving cross-country in a panic to get
to the next show on time. In that case I used a dremel with felt
cones, it left slight wavy surfaces of course.
Polishing stone (or glass) is really a process of finer and finer
scratching with smaller and smaller abrasive particles. Usually even
minor looking scratches are deep enough that their removal means you
have to start by lowering the surrounding surface with a more
aggressive abrasive than cerium oxide alone – thats usually the final
polish after finishing intermediate steps.
Some stones - notably malachite and turquoise - are soft enough than
you can simply buff them on a regular cloth wheel with yellow rouge.
They do tend to become lumpy if you take this too far, but it will
work fine in a pinch if you’re careful. Alan Heugh