This video shows masking  a Tibetan tsa-tsa figure. The stone is porous with a lot of holes in the surface.  The gold  will adhere to the stone surface  and get into the holes so it is better to mask around the target area.

For more on traditional, lacquer based kintsugi see kintugi.com or https://zac.wnz.mybluehost.me/website_a640e8d6/?page_id=225