Once the pot is fired, this is not the end of the potter’s involvement in its production, as a number of procedures can be used to further improve its appearance or increase its strength. Most commonly these treatments involve applying a number of organic materials to the pot while it is still hot from the kiln, such as coating the surface with something to close the pores of the vessel, and make it waterproof. Sometimes tree resin is used, although some foodstuffs can be applied as well: for example, milk is swilled round the vessel while it is still hot, so that the scalded milk seals the interior surface. The decorated surface of a pot may be enhanced by rubbing certain things over it to polish it or, as in the case of lustre vessels (above), to rub off the earthy pigment and bring out the lustrous sheen of the metallic oxides.