Raku firing is an ancient Japanese ceramics technique that has been used for many centuries to create a very unique finish to wares. The Raku technique dates back to the 16th century, traditionally crafted by hand and not thrown on a potter's wheel.
The Raku technique is essentially when glazed ceramics are taken from the kiln while they are still glowing red hot and are then placed in a material that would be able to catch fire, such as sawdust or newspaper. This technique is used to starve the piece of oxygen, which creates a myriad of colors within the glaze. Raku firing without glaze on them means that the oxygen is taken from the clay itself rather than a glaze, which results in some areas having a matte black coloring.
Raku firing creates completely unique pieces as there is never a certainty as to how the final piece will turn out. Raku essentially creates a unique design every time, so there is less control on the outcome.