Greenish colour on hands from clay?

[Liam V]

I'm very new to pottery, I recently bought and repaired a second hand Venco wheel.

I've also just noticed that when I press my hand or sponge down against the moving wheel, anything that comes off it is a dark greenish, grey sort of colour.  I have no idea what is causing this but it mixes into my clay and darkens the colour slightly. Does any of this sound at all harmful or would it compromise the clay?

I've tried holding a sponge against the wheel without any clay and the colour has stopped appearing. I'm not sure if it's always been happening and I've only just noticed or something is causing it.

My guesses are:

- I just bought a piece of dry wall to wedge the clay on, something could be leaching off it into the clay?

- The sponge itself is somehow bleeding a dark grey green colour?

- The wheel has some sort of green rust that is rubbing off when I hold anything against it?

- I am using a yellow iron stoneware clay. This might react with something and create a dark green colour?

Have any of you experienced something like this and can help me identify what it is?

[Mark C.]

Wheel heads are aluminum and they shed oxide-a dn maybe combined with you yellow stone ware you get green. I would not worry about it. Others have posted color issues with their wheels and it always  is a moot point. Keep working . Its not harmful .

[Liam V]

That is definitely reassuring, thank you so much!