Traditional Japanese swordsmithing forges are fueled by softwood charcoal which is first chopped, screened, and sorted into several sizes for different stages of the forging process. The “furui” (篩) or sieve is used to separate different sizes of charcoal during the sumi-kiri process. This one is the smallest mesh of the four, made from window screen, and saves the fines for the charcoal bed and allows the powder to fall through. See the whole museum forge project here.