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hantremmer

Dealing with black oxide on wheelhead after throwing?

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As I've said elsewhere, I've just bought a new Shimpo VL Whisper RK3E.  CLeaning up after throwing, my sponge ended up with black sooty particles all over it.   Large black patches of the stuff.  The shop said it was oxide from the aluminium alloy wheelhead.  It's supposedly to help minimise corrosion and shouldn't affect fired ware.  (I was told that the oxide is normally white or grey, but small particles appear black.)

The thing is, I've never seen this stuff before, so don't know how how to deal with it.   Is there some kind of clean up regime I should use, or precautions I should take before / after throwing?   I normally clean my wheels with the sponge I throw with, but now I don't know if I should do that or not.

Any tips?

 

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wet sponge and wipe wheel is all I have ever done in the last 45 years-Its always worked. Never seen black oxide on a wheel head-alumunum will for an oxide coating over time but its not black.

Any wheel -all wheels are made to get wet and be sponged off.

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Mark,

Thanks for the reply, but I think you might have missed a word "alumunum will for an oxide coating over time but its not black".

 Because I've not seen it before either - and I've used three other types of wheel - I'm not able to guess what it might be.

It really was very strange.  The wheel didn't show any of it, but the spong had big black clouds of the tuff all over it.   It did seem to lessen between me rinsing the sponge and going back to the wheel.

 

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I wonder if it is maybe aluminum sulphide being created by sulphur impurities in the clay reacting with the aluminum in the wheelhead?  Not sure if that reaction will take place at "room temperature"........ don't think so.  But the color fits (dark grey). 

best,

.......................john

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31 minutes ago, Benzine said:

Any wheel head, I've ever used, leaves a dark grey residue on the sponges, when cleaning them.

Same here.  Shimpo Whispers at the college do it the most that I've seen.

best,

.......................john

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Thanks, everyone.    When I wipe the wheel down I'll often squeeze the sponge out into my reclaim receptacle.   Is that OK to do with the oxides in it, or it is best to rinse the sponge down the sink?

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The black stuff is a slight amount of aluminum oxide that abrades off the aluminum allow wheelhead when you rub it with clay on your hands or sponge. It happens with all clay, but is more visible with white clay or porcelain.  Aluminum oxide is one of the standard oxides in clay and glaze, so there is no adverse reaction that will occur if it is left on your sponge or clay. Even though it is black in color, the color will disappear when fired. There is not enough aluminum oxide involved to materially change the chemistry of the clay or any glaze on top of it. If your sponge has a lot of clay on it, squeeze it out in the reclaim bucket, no problem.  If you still get some residual black on your sponge during the final wipedown of your clean wheel, rinse in the sink drain.

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51 minutes ago, Dick White said:

The black stuff is a slight amount of aluminum oxide that abrades off the aluminum allow wheelhead when you rub it with clay on your hands or sponge.

If it is abrasion, wouldn't that be aluminum metal then?   (fits..... a grey color..... but darker?????)

And isn't aluminum oxide whiteish?  the CAS version 1344-28-1 version is.   

best,

.........................john

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My considered opinion on the practical side without submitting my dirty sponges to an analytic house for spectroscopy: The wheelhead is probably not pure aluminum, rather is an alloy of some sort? Never tried rubbing my wheels (including those of the school and community centers, various brands and ages) with sandpaper to examine the abraded content, only that which happens naturally through use. Plastic wheelheads (ClayBoss) don't do it, nor an ancient steel one, only aluminum alloy wheelheads. If one leaves clay debris (esp. porcelain, where is Nerd when we need him to explain the chemistry behind it:P ) on the wheelhead, it will discolor. (Same thing as aluminum barrels on pugmills vs. porcelain.) Then you can "polish" it shiny again with a bit of white clay and water as a fine abrasive, but the abraded slurry will be black on the sponge or your hand. If the clay is brown/dark, it will still happen but you just won't see it as clearly as black on white. If you polish it long enough with intermittent clean sponge squeeze-outs, it will stop coming up black, suggesting whatever black oxidation has now been removed. The same will happen if you don't use the wheel for a long time, the surface of the aluminum will oxidize very slightly, perhaps imperceptibly when looking at the dry wheelhead, but the black slurry will come up as soon as you hit it with the white clay/water/sponge.  As for color, yes the ceramic grade alumina oxide or hydrate is a white powder. But aluminum oxide sandpaper/grind stones/etc. are not white. And black is just concentrated gray, perhaps made to appear blacker than gray by the water? And so I stand by my opinion that it is abraded oxidized detritus from the aluminum wheelhead, and of no significant consequence to the ceramic ware in process.

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I know it makes no difference. ceramics-wise  .......... now I am just curious since it is being discussed here........ exactly WHAT it is.  Never thought too much about it before.  As I said earlier... not having thought about it much , I thought maybe it involved sulphur compounds in the clay.

I know from my amateur radio experience (I'm a ham) that the aluminum tubing used for antennas does the same thing.... and you get lots of blackish mess on you when handling the tubing when building one.  And for good RF connections we clean the crap out of it where it joins and put on an  anti-corrosion preventer.  Always assumed not that it is the oxide of aluminum.... but that it was corrosion that happened from other crap in the air.

Enquiring minds want to know............  ;)

best,

.......................john

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Well, maybe it is aluminum somethingelse. Perhaps rather than the precision implied by the word oxide we should use the undefined words tarnish or corrosion? Googling tarnish and aluminum tarnish leads to a lot of commentary about alkaline detergents causing darkening of aluminum cookware (sometimes the explanations involve atomic hydrogen too). Sounds like fluxes for clay to me. (Queue the trumpets for the entrance of Nerd to tell us about Na vs. K in clay bodies...). But exactly what is the black residue - oxide, sulfide, hydride (did I just make up a new chemical word) - ? But back the hantremmer's original question, I think we are all in agreement that it has no consequence to the clay/ceramic outcome. Or at least many of us have seen the black goo and suffered no consequence from it. Just part of the deal here.

 

dw

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Thanks for all the replies.   GOod to know I don't need to do anything special.

The shop said that it was a form of oxide from the aluminium alloy wheelhead; it normally looks grey/white, but particles that small appear black because of the materials optical properties.  

Perhaps that will help you pin down what it might be.

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Na5AlO4.  sodium aluminate

Nep Sy precipitates 14-20% soluble sodium salts. Notice the complaints about black specks have increased over the last five years as Nep Sy has become the flux of choice.

Normally soluble salts would form white crystalline nodules or powders in clay or glazes as they dry. However, every time sodium (Nep Sy) comes in contact with moisture, hydrolysis occurs: IE- hydroxols. So sodium hydroxide is coming in direct contact with aluminum ( wheel head) so instead of precipitating as white powder, it is picking up alumina to form sodiumaluminate that produces black/silver specks.

my best shot..Nerd

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It's copper in the alloy.  Machined aluminum parts are generally made from aluminum 2011, which contains up to 6% copper to make it machinable and give decent strength.

The clay abrades aluminum metal or oxide (doesn't matter which, aluminum oxidizes in minutes--why it's evil to weld).

Def not sodium aluminate.  That reaction's pretty exothermic and requires lye.

Edited by Tyler Miller
reverted to original version, removing incorrect info
Marcia Selsor likes this

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51 minutes ago, Tyler Miller said:

It's copper in the alloy.  Machined aluminum parts are generally made from aluminum 2011, which contains up to 6% copper to make it machinable and give decent strength.

Duh!  Thanks Tyler.  The brain hears "aluminum" when we talk wheelheads... and the brain assumes PURE aluminum.  Makes sense.  Best thought I've heard yet.

best,

......................john

 

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I forgot to add that perhaps the reason I've not seen it before is that my tutor's wheel looks to be something from the 70s or early 80s.   I've no idea what the wheelhead is made of.   My first home wheel was a Shimpo Aspire on which you needed plastic bats to throw.

I'm also using a clay that bisque fires to a lighter colour.  The name escapes me right now.  

 

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