The Mystical Golden Void of Medieval Art
Medieval artists painted heavenly figures against backgrounds of solid gold to represent a space outside of our reality. These shimmering walls of real gold leaf were not meant to depict actual places, but to suggest a divine, timeless atmosphere.
By covering the background in pure gold, artists effectively stripped away time and location from their subjects. This technique turned icons into windows that existed in a realm beyond the physical world, which is why the light seems to glow from within the painting. It was a brilliant way to make religious art feel both sacred and otherworldly. Even today, these surfaces catch light in ways that paint simply cannot match.
Source: Gold ground