Pronounced ‘rah-koo’ in North America, the Japanese pronounce it as more of a ‘gah-koo’ or ‘lah-koo’. If we wanted to put a Canadian spin on it, then it would be pronounced ‘ray-koo’ for the eh! factor. In Japanese the word literally means ‘pleasure’ or ‘comfort’ but in the pottery context refers to a process by which pottery is fired at low temperatures (by pottery standards – only 1850 F!) and then moved while hot to a closed container with combustible materials that ignite and cause a reaction creating colors and patterns in the pottery’s surface.
“Raku is committed to the basic premise that the pot is the product of a process of mutual interaction and refinement between man and nature and that through this involvement man discovers his own significance” – Whitaker, 1983
The Science of Raku
The process to obtain the amazing and varying results from a firing involve and Oxidation and Reduction atmosphere. In an electric kiln oxidization is occurring as you bring the glaze towards its maturing point. Oxygen is entering the kiln through peepholes, a damper (if you have one), and other cracks or gaps in the kiln construction. The metals (iron, copper, etc) added to the glaze mixture at this point are changing state to an oxide. An example of this process that is more commonplace is where iron rusts – its gains water and oxygen and therefore oxidizes the surface. This process sets the stage for the reduction process.
A reduction atmosphere in the North American technique is achieved by pulling red hot pieces of pottery from the kiln after they have oxidized and plunging them into flammable material such as newspaper, sawdust, staw, etc. As the material ignites it produces yellow flames, rich with carbon. An example of this process that you may be familiar with is putting a pot or pan over a recently ignited campfire – you’ll find that a lot of soot is deposited on the bottom and sides of the pot; this result occurs because there is a lack of oxygen reaching the fire, causing incomplete combustion of the fuel source. This reduction environment in raku is what changes the state of the now oxidized metals in the glazes to different oxides. For example a red iron oxide will change to black, while a green copper oxide will change to an orange/red.
As the yellow flames wick up the sides of the pottery the carbon acts on the pieces and alters their states to produce varying degrees of reduction effects. For example a section of the piece may turn from green to red (such as in a copper reduction), while another component may not be fully and stay green. In addition to this, glazes sometimes contain different metals producing an even greater variety of effects and colours. This process is enhanced by regulating the container that holds the flammable material by covering it with a lid to further starve the pieces of oxygen. This forces more intense effects as the flames desperately search for oxygen and “pull out” the oxygen from the oxides and in the example of the copper oxide produce elemental copper on the piece and carbon dioxide, which is vented out as a gas.
Check out this short segment of how we raku.