Japanese ceramics - Jan Kollwitz In his workshop in Cismar (Schleswig-Holstein) Jan Kollwitz creates ceramic works using a traditional Japanese technique. Since 1988, he has been firing his pieces in an original, wood-fired anagama kiln. Colour and surface effects develop on the unglazed ceramics during the four-day firing process. In the heat, fly ash fuses on the vessels to form a natural glaze. Smoke, flames and embers leave their trace as grey, red and deep-blue tones.