The lid of the Pyxis of Zamora sis decorated using the niello or enamelling technique. Niello is a goldsmith's technique applied to metal by inlaying a black enamel into grooves or incisions previously made in the surface (Moss, 1953), which is then fixed to the piece by applying heat.
The niello technique
It was customary to complete the decoration of some pieces of ivory work with clasps that contained nielloed details, pictures or areas in black or blue, which contrasted with the white of the ivory.
This technique enjoyed great favour in the Caliphate period, being widely used in the workshops of Medina Azahara, which allowed for colour effects in certain elements of the ironwork on chests and pyxides (Makariou, 2000).
Niel was the paste obtained by mixing silver, copper, lead and sulphur (Cambil Campaña, 2014).
Sulphur and, frequently, boron salt were used to facilitate the melting of the metals. The paste was melted and, once cooled, ground to a fine consistency so that it could be used to fill in the metal incised decorations. These decorations were often geometric, leafage or animal motifs and, in the case of pyxides, were made on the clasps with a dual functional and decorative purpose.
Bibliography
― Cambil Campaña, I. (2014). La orfebrería hispanomusulmana. Las joyas del museo de la Alhambra. Recuperado 10 de marzo de 2015. Disponible en: https://www.alhambra-patronato.es/wp-content/uploads/2019/05/Joyeria_I_Cambil.pdf
― Makariou, S. (2000). La Andalucía árabe. Institut du Monde Arabe; Fundación El Legado Andalusí; Junta de Andalucía. Consejería de Cultura.
― Moss, A.A. (1953). Niellon. Studies in Conservation.