Charcoal is chopped and then processed through four sizes of screen, the largest is for tanren, the second for hizukuri (I tend to use the largest for hizukuri as well and keep the second size mainly for yaki-ire), the third size isn’t useful in daily forging activity but may be crushed into fines or saved for tatara, the fourth is the fines for lining the bottom of the forge, and the remainder is dust for mixing into yaki-ire clay or for brasque refractory.
When chopping, the ideal is to produce cube shaped pieces approximately 1 sun in size. For the most part, the smaller sizes come naturally as the charcoal breaks. Although chopping perfect charcoal is very difficult, the majority of the charcoal should end up at the large size with much smaller proportions as the screens get finer. Measurements for the screen sizes are given in sun-shaku and the type of charcoal they keep in is listed rather than what they allow to pass through.
= 0.1 shaku（尺）
= 1 sun（寸）
= 10 bu（分）
= 100 rin（厘）
**Three things to note about this video:
1. after setting up, I moved the camera orientation 180 degrees and rather than move all of the charcoal i moved only the chair to the opposite side, but for efficiency it is a good idea to have the charcoal at the left side within reach of the non-chopping hand.
2. rather than chopping directly into a screen as I do, the normal procedure is to chop onto the tarp and then rake most of the largest charcoal off the top by hand before screening the remaining pile (see Pierre using this method).
3. also, some of this charcoal is quite soft having been heated too quickly in the kiln or overcooked so it looks more crumbly than it should.