These pots have a white slip applied to the inside including the lid, to allow a better colour response from the celadon glaze inside. The outside is left as bare clay with the intension they will be decorated by the kiln during the firing. The flame will carry soda/salt or fly ash from the wood depending on the firing throughout the kiln and will pass each pot individually leaving a flame path as it travels making each pot individual. As the temperature in the kiln rises the salt, soda or ash will become silica on the surface.
The clay is a blend of a high iron body and a white high silica body. The white body helps soften the bare clay, silica from the atmosphere within the kiln can attract to it more easily and the high iron clay gives that warm toasted red to brown look, traditional to the firing process on reduction fired stoneware.
For the body of the large Lidded casseroles I use 2kg of clay and for the lids of this size I use 1.3kg of clay. The reason for using so much clay is design feature for its intended use. These pots are used for slow cooking in the oven and not intended for cooking over a flame or on a hob. The thickness within the walls of the pot helps radiate the heat through the food, helping with the process of slow cooking. In addition, when taking from the oven to serve at the table food is kept hotter for longer for those second helpings.