Most any low or no sudsing soap will work as a burnishing compound. I use
diswasher detergent (1/2 tspn) & add about 2 oz (a shot glass) of
household ammonia to the mix as the only liquid. This all goes into a
vibratory tumbler with about 7# of mixed shapes of shot. You may want to
adjust the quantities for your size tumbler. If Murphy’s Oil Soap is a
low/no sudsing soap it should work, but why buy it if you’ve got dishwash
The ammonia-detergent mix does a good job of keeping the carbon steel shot
from rusting if the cover is kept on the tumbler tightly when not in
When the shot begins to feel gummy or looks grungy or like it may be
starting to rust it’s time to clean it. Actually, depending on how often
you use it, it’s really better to set up a cleraning schedule. Clean shot
does a better burnishing job than dirty shot. Any dirt mixed with the shot can
cause metal being burnished to be pitted, or roughened. The amount
of pitting/roughening depends on the size, quantity & hardness of the dirt.
To clean it cover the shot with water & pour in some Draino or lye. Let i
t run a while & rinse off the shot in hot/watrm water. Dry in a bath
towel & return to the tumbler. If it’ll be used right away add the
soap & ammonia, otherwise let it dry & replace the cover thightly.
A good stainless steel shot will solve the rusting problem, but it’ll still
need to be cleaned from time to time. In the US stainless shot sells
for about $13.00 a pound. Thunderbird Supply in Gallup New Mexico has the
bes t prices I’ve been able to find.
The polishing media in a rotary tumbler should fill the container just a
little over 1/2. When in operation the media assumes the shape of a small
hill with the bottom of the hill being carried to the top by the rotating
tumbler. When it reaches the top, because of gravity, some of it slides t
o the bottom faster than the barrel rotates. The polishing/burnishing
takes place in this sliding layer.
I’ve never used a barrel tumber to burnish silver, so I can’t estimate the time
required. A small vibratory tumbler does the job in about 1/2 hour
o r less. The new magnetic tumblers also take about 1/2 or less. The 5
day (120hrs) figure seems about right for polishing rock depending on the
grit & material.