A little while ago, I went looking for a video to explain the oxidation/reduction aspects of raku so I could assign it for my students to watch while I was out of the classroom for a day.
Sadly I didn't find one, but I did come across this video from the inaugural ASM teacher camp in Butte, Montana. It doesn't explain the redox aspects of raku - though the title suggests that it might - but it does include your friendly, neighborhood blogger in his orange polo shirt (ASM-branded, natch), and jeans.
Because the video doesn't explain the science, I'll give a quick version...
- We use a clear glaze into which we mix oxidized metals (cobalt oxide, iron oxide, copper carbonate, nickel oxide, etc). Each glaze gets just one of those oxidized metals.
- The pottery is taken out of the kiln while it's hot - somewhere around 1050 oC. At that point the glaze is molten, allowing oxygen to leave the glaze.
- The hot pottery is placed into a metal can with something flammable. In this situation we're using torn up newspaper.
- The torn up newspaper catches fire and starts to consume the oxygen in the now-sealed can.
- The carbon and hydrogen from the paper continues to 'search' for more oxygen, so it reduces the metal in the glaze and takes the oxygen from the oxidized metals. (This only works if the pot is hot enough for the glaze to stay molten in the reduction environment.)
- The glaze cools, sealing in the now-reduced metal within it, leaving - hopefully, if everything works right - reduced, shiny metal in the glaze.
- The pottery is quenched in water to lock in the final version of the metal within the glaze - either reduced or oxidized metal.
You can see lots of versions of raku pottery on other blog posts.
