First, let us talk about the soil in Nigeria: it is quite rich in clay, most often red or orange ochre but sometimes yellow. It contains pebbles of diverse grains, with an abundance of laterit, mica, ochre and feldspar. Mixing them with water, craftsmen would prepare rolls ready to be sculpted and perhaps assembled after firing. It is, indeed, not rare to find statue trunks with holes in place of the legs or arms. Once modelled and fired, the limbs were then assembled to fit on the trunk.
The soil presents a great variety of pebble dimensions and presents large aggregates considering that a piece must have been very eroded by water or rolling movements this also explains why the thin glaze has disappeared.
However, on the best preserved pieces, the glaze is so well treated that it gives the impression of real human skin, with a soft and pearly surface and a perfectly silky smoothness.
Certain traces of polychrome have also been found, souvenirs of time when anthropomorphic statues, some of them life-size, had to be very realistic and strongly colored.
Moreover, the soil was shaped only by hand, without tools. The experience of utilitarian pottery evidences early firing methods for millenniums. Certain works were dried in the sun, others in the ashes of an open fireplace at approximately 300°C, others at even higher temperatures giving them more durable surfaces. The craftsmen who worked in the surroundings of Nok used the same material for their statues as for their utilitarian pottery: a coarse-grained clay.
Some statues measure up to 1.20 meter high and weigh close to 50 kilograms, suggesting an excellent mastery of sculpting techniques as well as of firing in the open air. Since many statues are hollow, the sculptor took care to maintain the same thickness on the whole piece and to scoop out the parts that could have exploded in the fire.
Taking into account the size of the pieces that have come to our knowledge, the firing technique proves quite well the enormous talent, know-how and experience of the craftsmen of that period. How did they manage to fire in open or closed ovens these high and massive statues, some of human size, without making them explode during the firing process? These artisans found the solution by using tree branches and trunks as a central core of the sculptures. On these wooden cores, generally covered with grass, the artist applied the packed soil in the shape of rolls and sculpted his piece by hand.
Numerous fingerprints and marks are fixed forever in the heart of the terracottas, still visible messages of humanity capable of touching today's onlooker. During firing, the interior wood burned slowly thus conferring a perfectly distributed heat. After cleaning off the ashes, the charcoal, and the burnt straw and soil, the hollow and lighter column-statues finally appeared. This cleaning, done at present by our contemporary hands after a new find, still induces an intense emotion, exactly like when Egyptologists open a sacred sarcophagus.
So the Nok people possessed fire and the art of firing. This technical competence as well as the stylistic mastery exemplified by these works lead us to believe that Nok art could be the result of an already long artistic tradition. Signs of experimentation or research cannot be detected anywhere. The characteristics of this style were already, and still are, precise.