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Black spots on pieces after tumbling


#1

Hello All,

I have scoured the archives for a solution to my problem, but have
not found an answer yet, so I am posting my issue and question here.

My issue is that I am finding tiny black spots on pieces after the
Shell Shine Green stage in vibratory tumbler. I can scrap them off
with my fingernail, and I also tried cleaning it off with water, dish
soap and a toothbrush, both of which then resulted in tiny white
watermark-like marks in their place.

My question: how and why is this occurring, what am I doing
incorrectly, and how can I avoid this in the future?

(also, upon loupe ing a piece, I did also notice a few tiny cone
shaped protrusions which were each preceded by a drag line (they
kind of looked like volcanos!..strange, huh!?!) I am just
wondering how and why this is occurring as well (…just curious…as I
had been previously working with cast flat discs, and had run into
the problem of sub-surface pitting upon Tripoli/ rouge/
ultrasonic…but I digress…I figured out that situation after
scouring the archives…thank you all for that help!)

Anyway, any help would be greatly appreciated…

Task to save time on the finishing process of purchased,
die-stamped, 20gg, Sterling Silver BE" round discs.

Prior to tumbling, I take them out of the bag, drill the hole,
solder on a jump ring, and stamp with .925.

Goal a nice smooth shiny finish.

Previously I have been sanding with 380 thru 2500 grit sandpaper,
then hitting them on the polisher with Graystar Tripoli, then Blue
Picasso Rouge (Great stuff from Rio!)

But, this takes much too long. So I am investigating the Vibratory
tumbling process prior to purchasing my own set up.

My process has been:

I am borrowing a friends Raytech TV-5 Vibratory tumbler (a small
one, does not have flow-thru water system)

(2 Plastic medias run with deburring solution)

  • (A&A) Super cut pink cones (medium cut) (ran for 24 hours)

(probably didn’t need to run it this long, but as it is a fine
textured surface, I wasn’t sure if what I was seeing was the best it
was going to get, so I extended my original time…I checked the
results at 6 hrs, 12 hrs, & 24hrs…I hope this wasn’t a bad thing…)

  • (A&A) Fine cut aqua (fine cut) (ran for 24 hours)

(probably didn’t need to run it this long, but as it is a very fine
textured surface, I wasn’t sure if what I was seeing was the best it
was going to get, so I extended my original time…I checked the
results at 6 hrs, 12 hrs, & 24hrs…I hope this didn’t wasn’t a bad
thing…)

  • (Rio) Shell shine-green (run dry for 18 hours)

(probably didn’t need to run it this long, but as it is an almost
shiney surface, I wasn’t sure if what I was seeing was the best it
was going to get, so I extended my original time…I checked the
results at 6 hrs, 12 hrs, & 18hrs…I hope this didn’t wasn’t a bad
thing…)

  • (Rio) corn cob (haven’t done this stage yet)

In case it makes a difference, I also do possess a Lortone double 1
quart barrel rotary tumbler, 4lbs of mixed stainless steel shot, and
2mm and 3mm porcelain spheres (along with a burnishing solution), but
have not really experimented with this yet for this task, as I was
following the vibratory route first…

Thank you all in advance!
Julie


#2

Julie - you are working too hard with the wrong tumbler.

The tiny tv-5 has a lot to do with your problem. As you have pointed
out, it is not flow-thru. As a result, all of the junk that is
abraded from the discs is hammered back into the soft discs. Running
longer just makes it worse. It is so small that it is hard to imagine
it tumbling more than 6 or 7 one inch discs.

I would suggest this revised process -

After attaching your jump ring, run the discs for 30 to 45 minutes
in stainless steel in your rotary tumbler. Please use a liquid
chemistry appropriate to steel - I like Rio liquid sunsheen
burnishing compound for ease of mixing. This process slightly hardens
the surface of your textured discs. Rinse everything clean.

Second, since your discs are stamped, you don’t need the pink media,
it is more aggressive and might be the source of your cone shaped
protrusions - or maybe not.

Borrow, beg or purchase a vibratory tumbler with flow-thru
capability. A TV-10 goes for about $240US. If you can’t get one,
change the liquid in the TV-5 hourly. Run your pieces about 4 hours
in a fine media with an appropriate deburring compound. Your aqua
cones or triangles are appropriate fine media. If you have a very
detailed stamping, the triangle/pyramid shape might be a better
choice. After 3 to 4 hours, rinse and clean everything. Use an
ultrasonic cleaner if you can for just a couple of minutes.

Then run again in your rotary with steel as in the first step above
for 30 minutes.

If you want to further refine your surface, run the discs in a
chrome oxide charged mixture. I like the green buff better than the
green shell shine. I recharge the mixture with Simichrome, rather
than chrome oxide. The shell shine is coarser and will not produce
the refined surface you want. The green buff has much smaller mixed
sizes of stuff that is not as hard as the walnut shell mixture. My
typical runtime for a highly refined surface is 24 to 36 hours. I
almost never run high textures in dry media, it is enough to polish
the high spots with steel.

By using the steel before and after the abrasive step, you may be
able to omit the dry process altogether.

Julie, it really helps to have your detailed description of what you
have been doing. I hope that this revised process I suggest will
solve your problem. You could also get the book on tumble finishing
that I wrote for more insight on the processes.

Judy Hoch