Filling in a missing piece
This method avoids using a lot of gold but looks nice.
Using tile cutters nibble the replacement piece to fit the hole.
Insert and fill the gaps with putty
Carry on with repair as normal.
An opaque glass piece could be used so light can come through
Photo bottom left:
Then finish with metal powder. This one is 24kt gold leaf powder finish.
For this repair I used black urushi but no powder.