Adding kaolin to increase firing temperature

[Maougna]

Hello all , 

I have some interesting clay in my garden with which I have made nice pots  fired to 1250 ° C .  Suddenly the clay I’m digging up is a little different and it can’t quite handle the temperature. I tried adding feldspar but it’s still very unreliable . I’m just wondering what would happen if I added some kaolin . 
I’d be grateful for advice 

[Callie Beller Diesel]

Hi and welcome to the forum!

Pinned at the top of the Clay and Glaze section of the forum, we do have a list of articles and websites on processing wild clay, as it’s been a pretty popular activity in the last year or so, and lots of folks have been asking. Here’s a direct link.

If you’re dealing with a smaller seam of clay in your yard, it’s possible there’s a mix of a few different clays with different properties. If you want to use it regularly, it’s worth digging the amount you think you’ll need and slurry mixing it thoroughly so you get consistent results. 

At 1250 C (cone 6) feldspar should be behaving like a flux in a clay body, not a refractory. Kaolin doesn’t usually have significant amounts of sodium or potassium, so if you need your clay to warp/melt/bloat less, that would be a good place to start.