Another route that we have not taken is steel shot because such
an experiment may be quite costly and frankly we are skeptical as
to if this is the finishing route for us to take. Another route we
have taken is magnetic finishing with steel pin media. This,
however; seemed to leave somewhat of a pitted finish, not what we
were looking for.
Dear Mr. Nicholas J Griego, In my trips to India to work with
factory setups I saw that they did make a good deal of fine gold
jewelry. Fine gold is a bit too soft to polish well, in any type of
media. Even the most fine grit media will scratch if not bend this
type of product. 24kt doesn't even polish well with wheels and
brushes because the metal is too "plastic". Magnetic finishers are
a wonderful machines and yes, they will leave a finely pitted surface
on nearly all colors and karats of gold. The are really intended to
brighten the very recessed areas of an item before they are put into
the larger mass finishing equipment.
The way that this type of jewelry is polished in India is by hand
burnishing using a very highly polished piece of stainless steel.
There were rows of young men and women with the rounded end of about
a foot long piece of steel rod resting in a groove or hole near their
elbow. The pointed, polished end was in their hand and they used
this to burnish the surface and remove the shrinkage defects that are
inherent in pure metal castings. While I didn't like the full hand
method it did produce a nice finish in a practiced hand.
To achieve a "shiny" surface, It is likely that the one method that
you consider costly and have yet to try is the one that is necessary.
In castings of any metal, the smoother the model, mold, and casting,
the less finishing that will be required. You may need to do the
small hard to reach areas and the areas of shrinkage porosity by hand
burnished. If any abrasive is necessary, the lightest cut possible
should be used as the metal is so soft. Then introduce them in to
the "burnishing" stainless steel shot. A variety of shapes in the
stainless media would be advised but avoid shapes with points. I
would not recommend a vibratory finisher or any other high energy
finisher for 24kt jewelry as the metal is so soft that it will likely
dent the surface. I would suggest a simple rotary drum finisher
where the media and parts simply slide along each other at about a
45 - 50 degree angle as the drum revolves at 1 G. Yes, it is slow
and your best choice for this metal. A good (non-chelating) soap is
important. Don't forget to run your water through a settling tank
and an ion exchange column before it goes down the drain.
J. Tyler Teague
(Jewelry Engineering, Training, & Technology)