“Burnt” look near bottom glaze on tan clay

[Morgan]

Hope everyone is well.

I am playing around with a new clay body that is tan/almost peachy colored and it’s so lovely I did a few test tumblers with the bottom third clay exposed. On almost all of them, no matter the glaze, right beneath the glaze itself it produced and almost burnt/cooked color. The rest of the piece is fine, bottom etc just near the glaze itself. 
 

This clay is rated to cone 8 and my witness cones were all pretty much perfect ^6. I recall seeing this long ago when testing a bag of lagunas speckled buff so I’m not sure what would cause this. Glaze fumes perhaps discoloring the clay? 
 

I am 90% porcelain user so thought I would ask if anyone has seen this before.

[Min]

Sounds like sodium flashing. Does it look like the pots in this link?

 

 

[Morgan]

Maybe…it’s more the clay itself right beneath the end of the glaze line. Where the glaze ends looks fine just maybe a 1/4” or less below it gets the toasted look. I will try and snap some pics.

[Babs]

Folk try to get that look by applying a soda wash to unglazed clay. I think it is a fuming of the sodium as Min is saying.

It could be that the bisque is porous and a thin "layer" of glaze is migrating up the interior of the wall of pot as the pot is dipped .....maybe.

Edited August 28, 2022 by Babs

[Morgan]

Ok the more I look at those pics I think you are both correct, especially the second picture albeit not as pronounced. I suppose there is no real remedy to it and more of a clay body issue. Either way not a big deal I was just playing around with a few bags of different clay I had. 

Thanks all!