I personally don’t feel that tumbling can ever completely replace
buffing on quality work, however it does help work harden the surfaces
and it’s nice emotionally to be handling items that are already shiny,
and the shot will get into places that are hard to reach with buffing,
brushing etc., (and vice versa). Do everything just right and it comes
close to a buffed finish. I don’t like tumble grinding with abrasive
media because it, in my experience, leaves a film of abrasive on the
metal. (If someone has found the magic method that REALLY eliminates
that problem I’m interested.)
For silver:
THE FIRST THING TO DO is tumble just the shot over night or longer to
polish itself, in the anti- rust soapy solution (available from “Rio
Grande” and other suppliers) then wash the shot in a colander and
IMMEDIATELY add new anti-rust solution. Keep the shot pristine by
changing the solution often, otherwise you will be grinding and
embedding a film of grit into the silver - if you tumble polish stones
don’t use that barrel for silver, or at least scrub the rubber liner
twice, and rinse well.
File, sand, bob, or otherwise remove the flaws, bumps and sprue
marks, and refine the surfaces lightly with extra fine sandpaper or
with your buffer using spongy soft abrasive wheels (the extra fine
version from 3M Corporation, St Paul Mn.)
WASH OUT THE DIRT (use an ultrasonic cleaner if you have one)
and then tumble the castings* in VERY clean and highly polished steel
shot, What I think happens is the pure silver is smeared and burnished
over the fire scale, leaving it unnoticable, (use absolutely no
abrasive polish! - don’t let anyone talk you into using lapidary
polish. You will embed the abrasive into the silver’s surface and then
it will be much harder to buff clean.) I use a rolling tumbler - its a
smoother, sliding action than the vibrators, but others use vibrators
and now magnetic tumblers with apparently good results.
If you are tumbling stainless steel it will probably take longer than
silver, I don’t know how much longer.
Alan Heugh
http://www.nas.com/~aheugh/