Magnetic mystery

At work, we are having a mysterious occurrence with the little
magnetic pin tumbler. The solution (Rio Super Sunsheen Burnishing
liquid and water) is turning into black sludge that looks like a
Pacific oil spill. Sometimes there is just some black crud,
sometimes the whole jar is disgusting. The boss said to clean the
shot with denatured alcohol-- this has not helped at all. We tumble
all colors or 14k and 18k except green, which doesn’t go in there at
all, plus pt, pd and sometimes silver, though I try not to put silver
in because I hate the finish it gets that way.

Any ideas? The shot looks fine. It’s a bit low, so I’m going to order
more, but stainless shouldn’t deteriorate. We are at a loss to
explain it.


Noel, I use, Soap Powder for Magnetic Tumblers, from Gesswein and
tumble the same metals you do and the water still gets black. When I
can’t see what’s in the bottom of the bowl I change it. I just run
clean water through it and swish around the pins until it’s clear,
pitch in a tablespoon of soap and go. The bowl is about 3 years old
and the walls above the water line are permanently black, below the
water line it’s clean. The pins always look clean. It seems to take a
half dozen cycles for the water to get really black (sometimes with
little oils slicks). I have no idea what causes that?


you can order shot cleaner from your supplier. In the mean time you
can use Coke a Cola to clean the shot. Just use the coke instead of
water and run the tumbler with no product for a few minutes. Silver
is the culprit so I usually add shot cleaner whenever I am running
silver, at the end of the cycle everything is clean. Frank Goss

If you use coca cola, make sure it’s flat coke.

I found this article on website that explains why
tumbler barrels get black sludge and how to clean a contaminated
barrel. [PDF file]

Any ideas? The shot looks fine. It's a bit low, so I'm going to
order more, but stainless shouldn't deteriorate. We are at a loss
to explain it. 

Test the pH of the liquid, then use something with the opposite pH
to make it go away.

If your liquid in your tumbler is acid, clean it up with some ZEP
floor stripper (which I use in my ultrasonic cleaner) it’s very

If your solution is base, clean it with vinegar.

Paf Dvorak

you can order shot cleaner from your supplier. In the mean time
you can use Coke a Cola to clean the shot. 

Coke is acidic. But it’s full of sugar which will gum up the works
and cause more problems than you started with.

Use vinegar or lemon juice. Or dilute hcl.

Paf Dvorak

Hi Noel,

Are you using tap water? There might be minerals in that causing a
reaction with the shot and/or the Sunsheen and/or the metals. I’m
not a chemist, so I can’t really offer specific on what
dissolved minerals might be causing the problem, but perhaps
distilled water would solve the problem…(Bri M. are you reading

Hope all is well with you,
Linda Kaye-Moses

Thanks for the suggestions, all.

I should perhaps emphasize, this is not a rotary tumbler, and it
does not have a rubber barrel. It is magnetic, with a clear plastic

Nor does the problem happen all the time.

I will try some of these suggestions, but none really seems to
exactly match the problem. Still, nothing to lose! A little coke, or
vinegar, etc.


This isn’t a mystery. Change the liquid at a minimum daily. If you
have a batch of dirty jewelry, change it after the run. Black goop in
any tumbler means it isn’t getting clean - use the recommended amount
of soap. And if that isn’t enough, use a bit more - but add extra in
tiny amounts. This is a lot like a front loading washer, you need the
right kind of soap and not too much.

The black goop is exactly the same result - dirty media - as the
black goop people get in rubber barrels. Hello - it’s not from the
barrel or the media, it is from inadequate cleaning. Have you ever
tried to get a greasy cooking pan clean in cold water with a "drop"
of soap?

When you polish - do you carefully gauge the amount of polishing
compound on the buff? If it is caked, you would rake the buff. If not
enough, you would add a bit. Your media needs the same careful

Judy Hoch

Burnishing actually removes a very tiny amount of metal and metal
oxides, finely divided metal and oxides tends to all look black. The
shot and the work will both leave microscopic particles of metals in
solution. This combined with the crud that forms from the the
burnishing compound, dirt and other miscellaneous crap that ends up
in the tumbler makes that black gunk. A running it with in a strong
detergent then rinse and follow up with some citric acid in water
will clean and re-passivate the stainless pins.

James Binnion
James Binnion Metal Arts

Hi Linda,

I’m not a chemist either. (My parents were, and I grew up in their
labs, but that’s why I went into art.)

I’ve had that happen with my rotary tumbler, but I always chalked it
up to crud from the black neoprene barrel.

Jim Binnion’s theory about suspended micro particles of metal and
crud makes as much sense as anything I could come up with for a
magnetic tumbler.

Sorry, no stunning wisdom here.


This isn't a mystery. 

Give me a little credit-- I’m neither a rookie nor an idiot.

If the definition of insanity is doing the same thing and expecting
a different result, what is it when you do everything the same,
expect the same result, and get a different one? I’d say a mystery.

If you found a thick viscous black goo an inch deep in your tumbler
for no evident reason, every week or so, and a thin slick at other
times, but most of the time no problem at all, you’d probably be
mystified too.

We clean things in the ultrasonic before they go in the tumbler, if
they need it.

I appreciate the suggestions. Oddly, for the moment, the problem has
dissipated on its own. Go figure.


Noel - The black slime problem is common in all mass finishing media

  • it was clear that you were using a magnetic pin finisher. Anytime
    you have enough dirt/grease and not enough cleaning compound, black
    slime results.

Cleaning up the mess is common to all processes - coke or a
degreaser run for 20 to 30 minutes will clean it up. I use a diluted
commercial degreaser used by janitors to clean floors.

The cleaning liquid needs to be changed with each run. You wouldn’t
try to wash a cooking pot in yesterdays dirty dish water. The same
applies to the burnishing/cleaning liquid in magnetic pin finishers
and rotary drums. It also helps to rinse or ultra-sonic the jewelry
pieces prior to starting a polishing run.

Sometimes the black slime can result from overly long process
cycles. 30 minutes is long enough for steel in a rotary or a pin
finisher. Several hours will result in surface degradation and
detritus in the cleaning liquid and predictably - black slime.

If long runs are needed - the quality of the cleaning liquid should
be checked once an hour. If dirty, simply rinse, and replace with
clean burnishing liquid. Commercial processes have a flow-thru
system for rotary processes.

Judy Hoch