Charcoal used on marble as a temporary dark marking surface so compass points and reference marks can be seen clearly during point transfer.
Carbone da tracciatura is charcoal used as a temporary marking aid during traditional point transfer. In the Rino Giannini demonstrations indexed by Le voci del marmo, charcoal is used with the chisel to make compass references visible and to trace capopunti clearly on the white marble surface.
Etymology
Italian: carbone, “charcoal,” + tracciatura, “marking/layout.”
Sculptor Notes
This is a simple but revealing workshop trick: accurate measurement is useless if the mark cannot be seen. Dark charcoal creates immediate contrast on white stone and can be renewed as carving removes the surface.
References
https://levocidelmarmo.sns.it/lista_video.php