angboy, it depends on how deep the lines are cut/burned to start with. I had some that were too shallow and ended up sanding most of it out. The others were fine, but they were deeper to start with. So I went back and reburned them. Of course, I needed to re-etch them with a skew. Be careful when reburning, if you slip (like I did) then you get wire lines in the area around the burn line. Then you have to resand. After the several attempts I became real careful when reburning. So doing it before sanding is good, as long as you have them deep enough to not sand out. As always, YMMV. Good luck, Dale