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Mass finishing techniques


#1

Was: Hobby-store low cost tumblers…

I have changed the topic heading to better reflect the direction of
the discussion.

Mass finishing does indeed harden the surface of jewelry metals.
There was a detailed study done for the 2009 Santa Fe Symposium by a
number of scientists, metallurgists; many of them Orchid
participants. The initial question they examined was to see if
burnishing jewelry metals could reduce signs of wear. The study
included examination of time run in tumblers compared to hardness
achieved. One clear result was that rotary tumbler processing creates
a harder surface than the same time in a vibratory tumbler. It also
showed that running with 40 pounds of steel was more effective than
running with 10 pounds of steel. Big tumblers work better. The study
also showed that the hardening could be removed by subsequent hand
polishing.

When I started my early experimentation with mass finishing, I
discovered that hand polishing after burnishing was a disaster. I was
using sterling silver and the burnishing hardened the surface layer.
The surface did not display fire scale or fire stain after burnishing
but when that was followed by hand finishing, the fire stain
re-appeared. Hand polishing removes about 5% of weight of the
conditioned surface. Mass finishing techniques remove something under
0.25% of weight. These percentages are not precise, but in my
experience are representative of the differences between hand
finishing with aggressive compounds and mass finishing techniques.

I did not have the scientific instruments that were used in the
formal study so it was a simple critical observation. Instead of hand
polishing to get a nice smooth shine, I worked through a series of
steps and found a sequence that is workable. It varies by type of
metal. Platinum, sterling silver, varying karats of gold and various
alloys all require variations on this sequence.

For sterling silver - hand finish to the point where you would start
finishing on a buffer with Tripoli. I use a 6-quart flow-thru
vibratory tumbler and a 30-pound rotary tumbler with stainless steel
with chemically appropriate liquids.

Rotary tumbler for 45 minutes, vibratory tumbler for 4 to 6 hours
with fine abrasive media (Rio’s Clean Cut blue cones are an
example). Then 45 minutes in rotary, follow by 36 hours in vibratory
tumbler with charged dry media (wood chips with Simichrome, or Rio’s
green buff, both with 25% wood pegs). I started this whole thing
because I was making hand made planished big loop chains and
hand-finishing chain is not an option. This sequence yields a perfect
shine with no orange peel or haze. There are many variations of the
sequence - if you have textured or patinated surfaces, the long dry
vibratory sequence is omitted. The suggested sequence will produce
mirror finish on flat surfaces too.

Last summer I ran a series of experiments with PMC1, PMC2 and PMC3.
I had Cece Wire, a master instructor, create the samples since I am
not a qualified PMC maker. I ran about 60 samples in a wide variation
of processes. Then I packed up my studio and moved. My preliminary
results indicated that a sequence similar to that proposed for
sterling silver yields a superior finish to that of just using steel
with no abrasive step. I understand that some folks believe that you
must hand finish fine jewelry.

All commercial jewelry manufacturers use mass finishing. Mass
finishing is common in the fine European ateliers. Once you figure
out the sequence that works for your jewelry, mass finishing always
yields the same result. I believe that there is much to learn about
repeated hardening steps in finishing. Perhaps we can do another
study where we repeat the hardening after abrasive processing. Would
three times be better?

For more detailed you might wish to consult my book -
Tumble Finishing for Handmade Jewelry. It’s available from many of
our Orchid advertisers.

Judy Hoch - now in Salida Colorado
Marstal Smithy
http://www.marstal.com