Hi, I've read about people using clay balls as an addition to substrates. I've done a search, and can't find the answers I'm looking for, so please forgive me if this has been discussed endlessly. I was visiting a potter friend and scrounged a small bag of clay. To my surprise, it's white, not the brick-red that I usually associate potters clay with. Can I use it? And if so, what should I add, and how should I prepare it? Dry in the sun (erm, well, there isn't much of that at the mo!!) or in the oven? I know that @greystoke uses this, any advice please?