The manufacturer recommends kiln firing only.
We managed to fire it with a handheld torch. Though, we suggest following the manufacturers instructions.
Fring instructions: put more than 1 cm of coconut shell activated carbon on the bottom of a metal container. Place the piece in the carbon and fill the container with carbon more than 2 cm over the piece.
Place the container in the cold kiln and fire it during 2 hours at 820 °C.
Take out the metal box after cooling down.