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Black gunk in tumbler


#1

I’ve had an odd occurrence and I’d like to understand what made it
happen and how to fix it.

I have a set of castings from organic items (not that I think the
source has any impact, but figured I’d mention it). The castings were
cleaned and pickled, cut from the sprue and then tossed into my
rotary tumbler with stainless steel shot, water, and a bit of dish
soap – the same way I handle all my organic castings as the first
cleanup step.

Usually, the castings turn out nice and bright, I can clearly see
where I need to do cleanup and hardened nicely to begin more
fabrication work. The tumbler water is usually a bit gray - sometimes
even dark gray - but the pieces are nice and bright.

This time, I left it tumbling longer than usual, because I forgot to
turn it off before going to bed. It ended up tumbling about 24 hours
instead of my usual 8 - 12.

The tumbler barrel was still sealed and no leakage had occurred.
But when I opened the barrel, the water had turned to a thick black
"sludge" that coated the inside of the barrel with a layer about
1/2mm thick. It seemed impervious to water. The castings themselves
are very dark grey, and my steel shot has darkened significantly.
Washing them thorougly had no noticeable effect.

I’m now tumbling my shot in coca cola, which has yielded wonderful
results in the past.

Here are my questions…

  1. What IS this black sludge? (Nothing was black when it went in
    to the tumbler.) Why does it form?

  2. How do I clean my castings and get them bright again? Can I
    tumble silver in Coke? Or would that eat away the surface of the
    silver?

  3. Are there additives that I can put in the tumbling water to keep
    this from recurring?

Thanks,
Karen Goeller
@Karen_Goeller


#2

I have removed the black coating you are talking about by painting
the silver with paste flux, heating until the flux gets to the clear
stage and then quenching in pickle. I do not know where the black
comes from, I suspect that students throw work into the tumble with
rouge or dirt on it and use the tumbler for cleaning instead of
burnishing.

Terri McCarthy


#3
I do not know where the black comes from, I suspect that students
throw work into the tumble with rouge or dirt on it and use the
tumbler for cleaning instead of burnishing. 

Terri,

If this were a rubber-barrelled tumbler, or the one I sometimes use
at the school’s lab, I’d tend to agree with you. But it’s a good
Aubin with a clear hard-plastic barrel (the diamond-shaped kind).
I’m the only one who uses it, and can guarantee that nothing rouge-y
or dirt-y went into it. That’s why I’m so puzzled by what came out
of it.

One friend (a glassblower) suggested that maybe the black gunk is
actually powdered silver that has worn away from the surface and
into suspension. But there was a LOT of it and no suggestion that
the castings themselves are any smaller or have lost any detail. So
I tend not to buy that one.

I will try your suggestion about heating with flux, then quenching
in pickle. Someone else suggested trying the ultrasonic, which may
have any effect, too.

Thanks!
Karen Goeller


#4

The black gunk is a result of having even minute amounts of
investmest still on your pieces. The investment acts as an
abrasive. I don’t know what the black gunk is but I’ve gotten it
too, and it is very difficult, if not impossible, to get off. Try
using a strong jewelry cleaner like Tarnex or Conisseurs on it.
I’ve had some luck with that. If it’s sterling, you might try
applying a patina to cover up the “steely” color.

Good luck.

Peg
Senior Lecturer
Dept.of Biological Sciences
Northern Arizona University
Flagstaff, AZ 86011-5640


#5

That black gunk is the rubber of your rotary tumbler. The rubber
breaks down after a while and you have to replace the barrel. I know
that if you use anything with citrus essence (like lemon-schented
dish soap) in your tumbler it will make it break down faster, but
even without that the tumbler will eventually die. I suspect that
Coca Cola is harsh enough to “eat” the rubber.

I’ve had good luck with water and a splash of Simple Green. But I
only use my tumbler for cleaning Bur Life off of jump rings, so the
Simple Green may not work for you.

Good luck! (And replace that barrel.)

-Spider (needs to replace one of her barrels too)


#6

I’d like to add to this thread. I too had some tenacious black
adhere to some of my silver creations. I did not use a rotating
tumbler with rubber barrels. I used my Gyrock and steel shot with
simple green.

Needless to say it was tenacious. My class has restarted and I took
the silver items back to school, placed them in the pickle, then
into the rotary tumbler with burnishing solution for only 20
minutes. From there I used the steamer and then the ultrasonic. Most
of the nasty black is gone. I may redo one or two a bit.

In looking back, I had tried to shine up the steel shot with coke.
The black appeared after that. Go figure.

Terrie


#7

Rubber breakdown is a part of the “black gunk” but there is also
metal removed (a very small amount to be sure) from the work pieces
even in burnishing operations and this metallic powder appears black,
this is the same phenomenon that turns the buffing wheels black when
you polish. Even in a magnetic tumbler with a Plexiglass barrel you
tend to develop a “black gunk” if you do not change out your solution
often. So metal powder is also a component of the “black gunk”

Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#8

The only time I’ve had black gunk in my tumbler was when I tried to
use Super Sunsheen with my stainless steel shot. I switched back to
the powdered tumbling soap and haven’t had a problem since.

Janet Kofoed


#9

Hi Terrie,

In looking back, I had tried to shine up the steel shot with coke.
The black appeared after that.

FWIW

In my book, the best thing to use to clean grungy shot or tumblers
is Draino (the dry granular type). I’ve been using it for years 1st
with carbon steel & then stainless steel shot in a vibratory
tumbler. I use about 2 tablespoons of Draino & 2 oz of water for 5#
of shot. Let the tumbler run for 1/2 - 1 hr, dump the liquid down
the drain, rinse in running water, dry the tumbler out, return the
shot to the tumbler & I’m ready for the next load to be polished. If
you want you can use lye (sodium hydroxide) in place of the Draino.
Just be careful with the Draino or lye, if you get it on you, wash
it off with plenty of water, it can cause burns.

Just yesterday I helped a friend recover from a situation of a black
covered sterling chain she’d made. It had been left in the tumbler
too long & came out black & stiff. She had put it through the 'Coke’
treatment a couple of times, but it was still grungy. We put it in
the pickle pot (PH Minus) for about 20 minutes. It came out lots
cleaner, but still wasn’t really clean.

Next I put gave it a boric acid/alcohol dip for firescale prevention
& heated the entire piece to a black heat with a torch. While it was
still warm it went into the pickle. When it came out in about 5
minutes, it had the nice white look of well pickled sterling.

The amount of heating has some part to play in the whole operation.
A small section of the chain near one end didn’t come out as white
as the rest the 1st time. I gave it the boric acid treatment &
heated that section a second time. After it came out of the pickle
the entire chain was the same whiteness.

Dave


#10
    The only time I've had black gunk in my tumbler was when I
tried to use Super Sunsheen with my stainless steel shot. I
switched back to the powdered tumbling soap and haven't had a
problem since. 

The only time I’ve had black gunk in my tumbler was when I tried to
use powdered tumbling stuff with my stainless steel shot. I switched
to Super Sunsheen and haven’t had a problem since.

Reev


#11

I got the black gunk too. I used lacquer thinner to soak my mixed
shot in, washed it off and I was good to go. Lacquer thinner got it
right off. I have seen others on this forum suggest tumbling Coca
Cola in the tumbler to clean the shot.

Diane


#12

Hi Gang,

I have seen others on this forum suggest tumbling Coca Cola in the
tumbler to clean the shot 

I’m not sure of the recipe for Coke, I think it’s still secret.
However, I’d bet that one ingredient is phosphoric acid. Phosphoric
acid is an ingredient in most commercial rust removers.

Another good cleaner for cleaning up grungy looking shot is Draino.
When my stainless steel shot gets grungy looking, I add about 2-3
tablespoons of granular Draino & 2 oz of water to the tumbler & let
it tumble for 1/2 - 1 hr. Then I pour the liquid off (down the
drain), rinse the shot in clean water, wipe out the tumbler & return
the shot. If you want, you can substitute lye (sodium hydroxide) for
the Draino.

This method also works with carbon steel shot.

Dave