Burnishing
The process of enhancing the smoothness and shininess of a surface such as metallic pigment by polishing with a burnisher.
Enhancing the smoothness and shininess of a surface such as metallic pigment by polishing with a burnisher - a smooth, hard stone (such as agate), metal, or bone set into a handle. See also gilding.
Michelle Brown. Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).