I have done raku. I loved the experience. It was during a workshop organized by our potter's guild, where a guest raku potter brought in her firing equipment. We used a special clay; a very coarse stoneware clay. We bisque fired our pieces in an oxydizing cone 08 kiln before the workshop. Our guild only fired in oxydizing kilns. We glazed our pieces with special glazes.
Raku relies on a reduction firing to achieve its metallic lustres and textures. When firing day came, the guest potter installed her kiln and fired it up. Each piece was placed in turn into the kiln where it was heated by 4 large propane burners. When they glowed red hot, the kiln was opened and using 5-foot long tongs, you reached in and retrieved our piece. The tong marks in the glaze add character to the finished piece. You swing the piece around a couple times in the air to cool it. The still hot piece is then dropped into a waiting metal bucket containing some kind of dry organic material. I chose pine needles because we had loads of those. Other people chose sawdust, straw, newspaper,. etc.
So, the hot piece is dropped into a waiting metal container, on top of the pine needles and the cover is added quickly. That's where the reduction atmosphere is created. The organic material ignites and consumes the oxygen in there. Smoke is produced instantly as the pine needles ignite and run out of oxygen. After a few minutes in there, you remove the fired raku piece with the tongs and let them air-cool on a stone. And voilą: you have the raku process as we did it.
My piece turned out with a lovely metallic copper shine to it. The coarse nature of the clay and the tong marks really added character to it, too. Since there were many of us participating, only one piece was fired for each participant. It was loads of fun.
Lots. Love it! Sylvain has beautifully provided all the basics on the process. The special raku clays have a lot of grog so they can withstand the thermal shocks of the process. Best to start with something small and work your way up to larger pieces as you get more experience in how to handle all the steps that involve red-hot ware.
I'll also add that it's something best done by at least two people, as there's a significant element of potential danger. Wear a welder's face shield and welder's leather gloves. Make sure no one has long hair for obvious reasons. Survey the surroundings before you start to make sure there's nothing combustible around.
For my reduction medium, I like to use shredded slick paper---those advertising inserts we all get---and fresh rosemary. I knew someone who used dog kibble. The more oils in your reducing medium, the more likely you are to get the metallic lusters. You can leave sections of the piece unglazed and just get pure smoked black, too. Can be very effective as a design element.
Raku is for decorative ware only---the clay doesn't vitrify and pieces remain porous. Sometimes I India-ink my raku to bring out the crackles in the glaze. Also you can wax the pieces after they've cooled, and that helps them absorb less moisture & chemicals from the atmosphere----those often change the glaze colors over time. I have a couple of good glaze recipes, but this one's my favorite: