Charcoal can be used in kintsugi as a cleaning agent in either hard or powder form. You use it to clean the surface of the piece after the initial clean up, you use it with water. The charcoal must be hard wood, oak or something similar.
Kintsugi materials, charcoal
Number 10 silver and gold marufun are very rough and need a lot of filling in of the grains in order to be able to polish them to a smooth surface. As the graded metal numbers get larger the grains of metal get larger and the finished polish shows more visual texture. The texture comes from the lacquer that fills in between the grains of metal. The larger grains also provide a thicker layer of metal that is a lot more durable. They take longer to do the infil with lacquer and longer to polish back out to a finished surface. They are much more difficult to break through to black so it is less likely to mess up using grinds above #5
