This video shows polishing rounded, graded, #3 gold, step 5.  #3 gold can also be polished with a polishing tool but I have found the other, more labor intensive process gives a far better and even finish.  In the video I start for the first minute with a #2000 mesh stone but quickly switch to a #3000 mesh since #3 gold is so fine.    There are about 8 more steps after this initial polishing.  In the video it looks like I am not doing much but by the end of the 8 additional steps it will be a nicely polished seam of gold. Step 5 refers to this page,  https://www.kintugi.com/?page_id=225 For more on traditional, lacquer based kintsugi see kintugi.com