Why did Gothic painters often use gold backgrounds in altar paintings?

In Gothic altar paintings, gold was frequently applied to panels as a background color to enhance the work's refined decoration and visual impact.1

This practice was deeply rooted in the earlier tradition of mosaic art, where gold backgrounds were used to signify divine light. In that context, gold tesserae were employed to depict the light emanating from God, a symbolic convention that became standard in religious art by the 6th century. As Gothic painters developed large-scale works for retables (ornamental panels behind an altar), they continued this tradition of using gold to create a luminous, sacred setting for scenes and figures from the New Testament.21

Beyond its symbolic association with the divine, the use of gold provided a rich, shimmering surface that complemented the emphasis on minute detail and flowing, curving lines characteristic of the Gothic style.1