The background of this frame has been hit, deliberately, thousands of times.
Punching a ground is an old goldsmith's habit that carvers borrowed. A small steel punch with a shaped tip is struck against the recessed background of the carving, over and over, until the whole surface carries a fine, even pitting. It is slow, repetitive work and it is done before any gilding goes on.
The reason is what happens afterwards. Gold on a smooth surface reflects light in one direction, like a mirror. Gold on a punched surface scatters it in every direction, so the ground reads as a soft, dense glow. Set the two side by side - burnished leaves against a matted background - and the carving appears to lift further off the frame than its actual depth would allow. The relief is exaggerated by light rather than by cutting deeper.
It also means the frame keeps working in a dim room. When there is not much light to catch, a scattered ground still gathers what there is, while a polished one simply goes dark.