We are a relatively smallcompany concentrating in the production of
custom gold, diamond, and inlay jewelry. We have decided recently
that it may be more cost effective to tumble finish some of our
castings. Through trial and error we have encountered much
frustration with very little results. We just can’t seem to achieve
the finish we want after days of tumbling in different medias.
Main concerns are what type of tumbler is best for gold fine
jewelry, if any at all; as well as what type of tumbling media. We
are currently using a vibratory tumbler and are struggling with types
of media to use. Should we be trying to acheive a fine finish from
such a type of tumbler? I do not want to go into the types of media
we have experimented in because it is somewhat lengthy. 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.
We have used ganoksin before to help solve casting problems and the
feedback recieved turned ot to be quite useful. Any help would be
greatly appreciated.
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.
Best Regards,
J. Tyler Teague
JETT Research
(Jewelry Engineering, Training, & Technology)
Main concerns are what type of tumbler is best for gold fine
jewelry, if any at all; as well as what type of tumbling media.
We are currently using a vibratory tumbler and are struggling with
types of media to use. Should we be trying to acheive a fine
finish from such a type of tumbler? ... 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.
The good news Nicholas is that the vibratory tumbler is perfect for
what you are doing. In finishing gold jewelry, I would suggest a
two step abrasive process – such as Rio’s grey hone (10
microinches) then the green hone (3 microinches). I run each of them
for 8 to 10 hours. Please use the appropriate deburring compound for
the media - soap looks good, but doesn’t suspend the junk from the
process and gives you a less than professional result. Then
depending on speed needed, you could use steel in a rotary tumbler,
or the cheaper slower method is a mixture of organic materials - I
like wood chips with wood pegs, charged with simichrome - and run
for 12 to 24 hours. This gives a good smooth bright finish which
compares well to hand finishing.
If your castings are robust, alternately you could use a disk
finisher for much speedier results.
For more process detail, you could refer to the book “Tumble
Finishing for Handmade Jewelry.” The fourth edition expands on the
finishing of many metals, and also reviews the use of many of the
newer machines on the market. This is a self serving plug.