I'm looking to revive traditional spherical Motu functional cooking pots (from Central Province,Papua New Guinea) and need some advice from experienced potters. The Motu have not made pottery since the 1950's and most of those real potters have since died out, taking important information with them. The Motu people today have not inherited the information and only know second-hand stories.
I've gleaned enough information from anthropological/historical accounts about how the clay is hand formed into pots (paddle and anvil method), and fired (open bonfire which generally only lasted only about 30 minutes), but there's nitty gritty information about the clay itself that I need to pinpoint.
My main hurdle is getting the clay body right so the fired cooking pots don't finally crack when used on the gas flame of the stove-top. I experimented using a German Römertopf terracotta vessel on the gas flame and it cracked big time - obviously it's only meant for the oven, but I needed to test it out.
Every western potter I've talked to shakes their head and says you can't use terracotta vessels on a naked flame, only in the oven. Our human history of thousands of years of unglazed terracotta cooking pots on open fires suggests otherwise. Even today there are many cultures that still cook with unglazed terracotta pots on open fires every day. Unfortunately these people live thousands of miles away and don't tend to use the internet, so I can't conveniently ask them.
I've guessed it involves using a clay with increased temper, so I've sourced some raku terracotta clay. Will this be enough to handle stove-top cooking? How much temper would make the final vessel withstand the thermal shock of daily stove-top cooking?
I'd be grateful for any tips from your direct experience.