A carved wood figure, often the well documented nail studded nkondi form, is not itself a nkisi in the working sense until a cavity in the body, commonly the belly or the head, is packed with bilongo, a combination of earths, plant matter and other components chosen for the specific working, and sealed, frequently under a mirror or shell that is understood as a surface the housed spirit can see through.
Who may make and activate one
Constructing and activating a nkisi is the work of a nganga, a trained ritual specialist, not something an uninitiated person assembles independently, the carving alone, however skilled, is inert until that specialist's knowledge and ritual activation are applied to it, and a specific nkisi is frequently restricted further still, to a particular lineage or a particular owner rather than open to the wider community.
What this atlas will and will not describe
The nails driven into a nkondi figure are typically added one at a time during oath taking or petitioning, a use restricted to those with standing to make such a petition through the nganga. This atlas records that the object exists, its general construction and that its use is genuinely restricted and to whom, and stops there, since the contents of bilongo and the specifics of activation belong to a closed practice this reference will not detail.