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Wheel Head Leaving Dark Tarnish On Clay

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My wheel appears clean and silver, with no visible tarnish. However, when I pull my clay off the wheel, there is black/dark looking clay or slip where it meets the wheel. It's as though the wheel head is giving off a tarnish or the clay is reacting to the metal.

 

Will this cause problems when firing?

Is there anything I can do to prevent this?

 

I know I could throw with bats but I don't currently have any. I will go that route if necessary, but in the meantime, just looking to figure out what this tarnish is and if it's going to cause problems.

Thanks!

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do not worry about it.  it is likely that glazenerd has a scientific description, i only have a working history with this.  it is simply a reaction between the clay and the wheelhead metal. 

 

you can see something like it when you look at a matte glaze on a plate and see the cutlery marks.

D.M.Ernst likes this

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Yes, Glazenerd will be along soon and give us a better scientific answer. For the layman's answer, it is aluminum oxide. The wheelhead is cast and machined aluminum, and the clay (whether through chemical reactions or physical abrasion) will cause a slight amount of the aluminum to rub off onto the bottom of the clay or your throwing sponge as the wheel turns. It is harmless, will not affect anything in the firing despite its dark color now.

D.M.Ernst and glazenerd like this

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