Charcoal is more of a makie material but can be used in kintsugi as a cleaning powder. You use it to clean the surface of the piece after you have mixed it with some water.
Kintsugi materials, charcoal
Kintsugi materials, hemp fabric
Hemp fabric can be used to strengthen large fill areas. It is embedded into the sabi mix and care must be taken so it is completely covered by sabi and the threads don’t stick out.