Magnetic pin finisher sludge

I recently started using a magnetic pin finisher to remove the
investment coating a silver object after casting. I added water and
"Super Sunsheen Burnishing Compound" to the container of stainless
steel pins. After about 15 minutes of spinning I examined the
results and found everything: silver object, pins and container
coated with a sticky black sludge. I had to change the water and
burnishing compound four times to get rid of the sludge. Has anyone
experienced this? If so, how have you overcome the problem?

I had the same problem. it looked like a thin layer of tar. I stopped
using the burnishing compound and started using washing up liquid
instead. now it works really well with no sludge. I don’t know what
to do with the powder now though…


I have found that it does not take very much casting investment at
all to contaminate the solution. But the pins are really good at
knocking the last little bits of investment out of the hard places.
My trick is to reuse solution the from the last run for a minute or
so and then change the solution so any investment is flushed out and
the tumbling continues in clean solution.

But another possibility is that like most tumbling systems the media
works better after it has been run for a while. I am willing to bet
there are hundreds of craftsmen who have bought new tumbling systems
and been so disappointed in the first results that they never used
them again. If I get new plastic media or porcellain burnishing media
I will run it for several days, changing the compound now and then to
break it in. I would think that running your magnetic tumbler with
some bits of scrap for an hour or so should be enough to do the same

Hi Harvey,

Here’s a couple thoughts.

I’ve seen this with my magnetic tumbler, and unless you clean the
pins after every use, you will see the black sludgy stuff. My guess
is that it is a chemical reaction with the amount of casting skin
and the polishing compound. However, there is a couple of quick fixes
and suggestions.

  1. Coca Cola. On a hot day, beyond Coke Cola’s refreshing
    effervescent bubbly malted battery acid goodness, it is a superb
    cleaner for your magnetic tumbling pins. No kidding. It must be
    regular Coca Cola and only the Coca Cola formula, no substitutes, no
    diet (diet doesn’t work, could be the lack of high fructose corn
    syrup, LOL), but I always had a large 2 liter container at the

  2. Dawn. It’s not just for dishes, it’s a superb degreaser and
    lubricant for your silver stuff and stainless pins. Use about 3 drops
    per one cup of water.

  3. Polish in three steps not all at once. With casting, you have a
    lot “skin” to remove and the amount of water/chemicals vs. cast
    elements might be overloading the efficiency of the process. Break up
    the polishing steps. I would clean the pins with coke first to remove
    any residue from previous polishes, rinse everything well, add the
    Dawn for two of the three steps. The last and final polish, use Rio’s
    Burnishing Compound.

We forget sometimes that polishing, all polishing needs to be done
in steps. There isn’t a "one time it does it all for everything"
step. One kind of grit will remove the burs and this could be ceramic
media in a large vibrating tumbler. Then different polishing
compounds, whether it be a flex shaft, large motor, small tumbler or
magnetic pin polisher, needs finer and finer polishing compounds, be
it a waxy stick type, or Radial Bristle Brush, sand paper or tumbling
to achieve the level of brilliance as you require.

Hope this helps.
Karen christians

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