Gouache on Clayboard

I like using Clayboard but it's not easy. When you start the water sits on the board rather than soaks in like paper. Perseverance has been the bye work here because it has stamina. You can easily take bits out and get right back to the board just like rubbing out. Using a wiping rag is useful at the start to purge the water. You can easy go over bits and the final colour does NOT sink.
So ,it stays bright and clean. ideal ! 
They are a little pricey for sketching but if I have  sold a painting or two it's worth the treat.