Pit firing is the original method for “baking” clay.  It dates back nearly 30,000 years ago. Pit firing is an atmospheric process and all of the colors and patterns are derived from the process and what is consume in the fire.  Items that are burned will turn to vapor and will swirl around the pieces in the pit.  If the pieces are hot enough to have their pores open the colored vapor will enter the pore and stay there, if not pot will not have color besides black, gray, or white.