The Science of Raku
What makes fire?
• Fire happens through a process called combustion
• You need three things for combustion
• Do you know what they are?
Fuel
• You need something that will ignite
• Anything that can burn can be a fuel
• Wood, paper, oil, leaves, coal
Heat Source
• You need something hot to make the fuel start on fire
• We use the glowing hot pots
Oxygen
• Fire needs air to breathe or else it won’t stay lit
• Fire uses oxygen just like you and me!
What makes the glaze colors?
• The main color in raku glazes comes from a metal called copper
• Where can you find copper?
In Pennies…
The Statue of Liberty
What makes the color of copper change?
• A chemical process called oxidation
• Copper starts out the orange color like in a new penny
• When copper is exposed to lots of oxygen in the air over a long time it turns green like the statue of liberty
Normal Copper Oxidized Copper
Oxidation and Reduction
• In the kiln the copper doesn’t get oxidized, it gets reduced
• The fire consumes the oxygen in the trash can and changes the color of the glaze
• The reduced part of the pot will look red or like a copper penny
• The oxidized part of the pot will be green or turquoise
Which side was reduced?
Which side was oxidized?
What makes the white glaze crackle?
• The crackle comes from thermal shock
• Thermal shock happens when a temperature changes from one extreme to another
• The kiln is glowing red hot, but outside the air is much colder
• This shocks the glaze and makes it crackle!
Where else can you see thermal shock?
Ice Cubes!
• When you drop a frozen ice cube into a glass of water it creates thermal shock too!
• The ice is so cold inside a freezer, but the water isn’t as cold
• Thermal shock makes the ice cubes crack just like the white crackle glaze
• This is only a small part of raku science
• Get ready to learn even more when we fire YOUR pots!