Shilpa's right, in that in most cases this refers to fine painting over gold. However, if this is the same piece you are translating regarding the Pórtico da Gloria, then if you look at the figures, there is no gold underlying the eye areas (
https://www.spain.info/en/images/portico-gloria-santiago-com... - except for Daniel's eyebrows as he has golden locks. Everyone else has dark or grey hair, some of it detailed with gold over the top of this. So, not all the details referred to in this work are painted over/onto gold. Can you tell us if this is the Pórtico da Gloria you are referring to or another piece?