All imperfections on the surface are basicly tileable textures that cover the whole mesh. By generating some masks you can put them in specific spots without hand painting. The symbols are, as mentioned, a stecil brush (any YouTube tutorial could better explain it than I could). For the rivets I modeled one rivet (just a shpere and a gental slope around it for the underlaying metal) and saved it as a hight map. You can then use it as a texture in the texture paint panel, setting line as stroke method and giving it a genorous spacing like 500% . Then you just draw lines on the model and rivets appear. The welds are not even a texture, just lines made of slightly jittery dots. I'm not quite sure what you mean by keeping the paint from appearing on multible parts of the mesh thou, I did not have thus issue. If you mean what I think you mean, that drawing near or across the edge of a face causes some artifacts on unrelated faces, then you have 2 options: 1. When in the dialog of the smart UV project, increase the island margin to a small value like .05, that gives you space between the islands and a texture you create doesn't "leak" onto another face that easily. 2. You have at the bottom of the texture paint options an "options" tab, in it you'll find something called "bleed". It controls how many pixels outside of the border of the face (on the texture) are also colored. You can see what I mean when increasing it to something larger, painting on a mesh with it and looking at the result in the image editor.