Strange Orange Spots, What Is It?

[High Bridge Pottery]

Bought some white stoneware a while back, never really used it too much. Made some test tiles thinking it is probably some weird mould and would fire out. That didn't happen. What is the stuff? 

 

Wet clay, you can see the layer.

 

Bisque that is really bad

 

Still there when fired, not so much on these one as the bisque yet to be fired.

[neilestrick]

So it's still there after firing? I would have guessed mold, too, but since it's still there after firing, I would have to go with some sort of soluble mineral that is precipitating out. Is it only on the outside of the block? If you wedge it well, do you still see it?

[High Bridge Pottery]

I had thrown with it and was not noticible, still orange when bisque but goes dark grey once fired to cone 9

[Joseph Fireborn]

Orange speckled clay, you should go into business. 

[jrgpots]

This is just a guess. Around here everything is high in iron. Yet, there are white sandstone cliffs in Zion National park 20 miles away. over time the iron became concentrated into spheres of hematite causing the sandstone to turn white...Some bacteria in clay or sandstone ingest the iron, concentrate it, then excrete it. This is how moqui balls are made. The excreted iron turns into hematite. The hematite when ground up gives RIO. But the RIO is concentrated around the colonies of bacteria and not evenly distributed throughout your clay evenly. If this process continued, the clay would become more white except around the bacteria colonies. Thus producing a iron speckled white clay.

 

 

That's my guess.

 

Jed