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Steel shot going black


#1

Our lapidary club has a Gy-roc vibratory tumbler for burnishing
jewellery. The tumbler is loaded with stainless steel shot to which
is added “Rumble Brite” and water. In recent times we have had
ongoing difficulties with the water and the shot getting
contaminated. The water goes black after using the tumbler for half
an hour. No amount of cleaning in acids, boiling the shot etc. has
stopped the problem. When the problem is in existent the shot feels
waxy and a black residue is left on the fingers if you pick the shot
up. Has anyone any ideas on what is causing is and more importantly
how do we stop it from occurring?

Ray Wilson


#2

Has anyone used the barrel for abrasive tumbling recently? If so
there may be abrasive grains in the wall of the barrel leading to
some abrasion of the shot, this abrasively cut stainless powder will
appear black. Finely divided metal powders appear black in most
instances. If this has happened use a new barrel and reserve it just
for shot use.

James Binnion
James Binnion Metal Arts


#3
No amount of cleaning in acids, boiling the shot etc. has stopped
the problem. When the problem is in existent the shot feels waxy
and a black residue is left on the fingers if you pick the shot up.
Has anyone any ideas on what is causing is and more importantly how
do we stop it from occurring? 

It is not the tumbler barrel as the barrel is plastic rather than
rubber. I have used Bar Keepers Friend or cleanser to clean the shot.
I would clean the shot and try one drop of dish washing soap with the
jewelry. If you want to discuss it more, email me offline.

Richard Hart G.G.
Denver, Co.


#4

I never figured out what causes it, but the old-fashioned cure for
the condition you describe is good ole Coca Cola.Get a can or two
(depending on the size of your tumbler). Open it up and let it stand
until there is no more fizz. Clean out the tumbler, run clear water
through the shot, return the shot to the tumbler and add the
fizzless Coke. Run the tumbler for a full cycle or longer. When you
empty it out and drain it, your shot should be bright and shiny
again. If it isn’t, but shows improvement, repeat the process.

It’s worked for me on the same rotary tumbler for 20+ years. If it
doesn’t work, try changing your detergent or using bottled water.
I’ve had to change detergents a couple of times when they failed to
do the job. Don’t give up. It’s curable. It may never be as
brilliant as when you bought it, but it’ll be clean and shiny and
gray and not slimy and perfectly functional.

Dee


#5

James,

Thanks for taking the time to respond.

Unfortunately that is not the problem. The Gy-roc tumbler is used
exclusively with the stainless steel shot for burnishing sterling
silver jewellery. We have a separate bowl with ceramic shapes that
we use for deburring castings.

Ray Wilson


#6

Hi Ray - presuming the Gy-Roc tumbler bowl is the normal white
plastic, you have two or three things that could be causing the
problem.

  1. The work you are tumbling isn’t clean prior to putting it in the
    tumbler. Any grit, investment, or dirt should be totally removed.

  2. The chemistry of your water has changed. Try a run with distilled
    water to see if that fixes it. If so, chase down what has changed in
    your normal water.

  3. You aren’t using enough cleaning compound or the dry compound has
    settled out and is no longer the mixture it should be. Get a bottle
    of liquid burnishing compound and mix with water according to label.

  4. If you are using a closed system, check liquid levels. Always use
    a new clean mixture of burnishing liquid.

  5. If you have a flow-thru system, check how often you change your
    feed bucket of cleaning mixture.

  6. After every run with steel, clean the steel. Just fill the bowl
    with water, and rinse. Repeat at least once. I use a big perforated
    cone to drain each rinse. It’s an old kitchen tool.

  7. Is it cold where you run this process? If you have grease or
    polishing compound on the work, think about what cold water, grease
    and soap do. It’s a gooey mess. You can correct this with a proper
    burnishing liquid.

And you can clean up your mess with a can of coke, or vinegar, or
citric acid in water. Put the slimy gooey stuff in the tumbler, along
with some acidic liquid and run for an hour or so. Should do the
trick. Then rinse everything well.

The key to successful tumbling is cleanliness and repetition. Do it
the same, every time.

Judy Hoch


#7

I’ve had shot turn black on me once, a friend suggested running the
shot with a dose of cola (red tin). About 1/2 a can for about 1/2 an
hour did the trick.

John


#8

I had the same thing happen and cola did the trick, but it is best to
get real stainless to run in the tumbler as this shitty shot will
always cause trouble. There are different grades of stainless and you
can test them with a magnet before you buy the stainless shot for
the tumbler.