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Polishing conundrum

#1

This is a tale of two foundries… and I’m stumped. Perhaps someone
out there can enlighten me. Two months ago I had a dozen pieces cast
in sterling at a large casting house in Paris. (I’m writing from
France.) They came back just fine, with a light mat finish and I set
about polishing them. The areas that I wanted bright and smooth I
started with tripoli on a felt buff (on a few spots where my wax was
originally a little rough I used emery paper) and areas where I
wanted to keep the texture left by the carving tools I was able to
use the tripoli on a brush. I was able to move quickly on to
polishing with ‘jaune’ and 'rouge’and the results are great. Several
weeks ago I found a foundry locally. A one man shop. I had him cast a
dozen pieces. They came back matt of course, but duller that the
first dozen. I’ve had a bear of a time polishing them. In the areas
where I want to keep the texture (scratch marks really) I get nowhere
with the tripoli on a brush, and the brighter areas are taking much
longer to work up a polish. I went back to the local caster with a
piece from each group and we went through the whole casting process
together trying to figure out where the difference came in between
the two. The only thing he could come up with was that the first
casting house might have put them through a polishing tumbler. I’d
really like to give the local caster my business, but the time I’m
spending polishing these things is way to long.

This leads me into part two of this message. I’m going into small
scale production with these pieces. I have a small rotary tumbler
I’ve never used but am looking at buying a magnetic tumbler. I want
to polish my pieces witha minimum loss of any detail and texture. Can
I do this in the tumbler? From what I can gather I need to use steel
shot in the tumbler to burnish the pieces and this will remove some
of the very light textures on them, and not get into the undercut
areas. I had thought of using walnut shells, but get the impression
that that media is use in vibrating tumblers.

Any response will be greatfully appreciated. Cathy Icardo (in Anjou,
France)

ps. I discovered you all at Orchid a month or so ago and can’t
believe my good luck…

#2

Dear Cathy there is an alloy called antifire scale for silver it’s
about$4.88 an ounce U can get it from (Riogrande )that’s the
company’s name.that will solve the first problem.tumbling is a big
subject depends on what type of designs and shapes so my advise to UP
is .#use any method of sanding(sand paper)and sand the
pieces75%leaving some work to the tumbler#2there is ceramic
media(tumble media) use medium grade and tumble for few hours with
water and soup#3 use steel preferably stainless steel round shaped
with dry soup and tumble as UP desire from this stage U have
to decide the finishing of your pieces . Good luck Dikran N.

#3

Hi Cathy,

Just about any tumbler, rotary, vibratory or magnetic can be used to
polish (burnish) metal. I’ve been using a small vibratory tumbler for
many years with assorted shapes (rounds (bb size), flying saucers,
diagonal cut, & elongated octahedrons) of stainless steel shot.

A few pros & cons about each.

The rotary tumbler is available most everywhere in several sizes.
Costs is nominal. Can be used with many media. Polishing (burnishing)
speed is the slowest of the 3.

A vibratory tumblers are usually available from jewelers supplies &
in the US can be purchased a stores selling hunters & shooters
supplies for less money. They’re available in many sizes. Cost , about
$50 & up depending on size. Polishing (burnishing) speed is fast, 1/2
to 1 hour. Maintenance is basically washing out the tumbler & shot on
a periodic basis.

Both the rotary & vibratory tumbler can use the same steel shot.
Steel shot is available in assorted shapes & in packages of each shape
in the assorted package. It’s usually available in both carbon steel &
stainless steel. The carbon steel will rust & requires more
maintenance. Stainless steel is almost maintenance free, but costs
about $15.00/ pound in small quantities. Carbon steel is about 1/2
the cost. A small tumbler requires about 5 pounds minimum.

Depending on their size, very small crevices & other spaces won’t
get polished. Any scratches that are in the items being polished will
come out as shinny scratches. Tumblers don’t remove scratches.

Magnetic tumblers come in various sizes. The smallest are capable of
handling about 15 rings at a time. Magnetic tumblers prices start at
about $350 in the US. Magnetic tumblers use small (0.3 x 5 mm & 0 .5 x
5 mm) stainless steel pins. The media used in magnetic tumblers can
get into smaller spaces. The media for magnetic tumblers price starts
at about $35 per 1/2 pound. Tumbling times are in the 1/2 to 1 hour
range.

Dave

#4

Hello Cathy Icardo,

I’ve been using walnut shell in the small Lortone tumblers for at
least 10 years. I’ve only had limited success polishing firescale
from soldered pieces, so don’t know how it would work for your
castings. The best use of shell seems to be removing tarnish. A
couple of observations in that area: The shell comes in 3 grades - I
use the fine and the coarse. It is used dry, and needs to be
"charged" before use. There are several compounds you can use to
"charge" the shell. Rio lists them with their mass finishing
materials. Instructions are on the container, but it generally says
to mash the sticky compound into the shell and spread it around as
best you can. (I use surgical gloves when doing this.) Then tumble
the stuff for a while. Periodically, I recharge the shell. The
paste lasts a lo-o-ong time. Rio also sells pre-charged shell, but I
can’t offer a comparison to the “home-charged” shell for you. If you
have crevices, openings to hollow interiors (like beads) the shell
works its way in, and can become packed inside. Usually, tumbling
these pieces in the empty rubber barrel for 15 min or so loostens the
pieces of shell so they fall out. Usually, but not always. Since you
already own the rotary tumbler, buying some shell and charging
coupound wouldn’t be much additional expense for a potentially
productive experiment. Judy Hoch wrote a little book “Tumble
Finishing for Handmade Jewelry”, available from Rio. That’s probably
a better source of info. Good luck, Judy in Kansas

Judy M. Willingham, R.S.
Extension Associate
221 Call Hall Kansas State Univerisity
Manhattan KS 66506
(785) 532-1213 FAX (785) 532-5681

#5

Hello Cathy,

I’m not a tumbler expert,but a magnetic tumbler will slightly mark
your bigger flat pieces.It’s like thousands of little needles hitting
the surface of your items and little pits will be left on the end of
the tumbling cycle. In the more time consuming rotary tumblers, I did
not see this negative aspect since the little beads are surrounding
the items like you would use an burnisher to highlight a gipsy
setting. Most of the tumbling media are abbrasive and will cause a
slightly loss of metal. The best way of precauting the loss of
metal,is to work on your wax (or pewter) and make it as perfect as
possible.I really spend a lot af time on my casting pattern and work
on it untill perfection is reached.If you have it cast by a good
craftsmen,the end product will be exactly like your pattern,causing
you no trouble at all finishing it in relative short time. I’m sure
that other orchid members with more knowledge about tumblers will
answer your question,but remember machines are made for machine work
and never replace our handwork .

Regards Pedro
Palonso@t-online.de