ArtMetal

Pinhole porosity can be a problem with gold castings. Usually, the first remedy I'll try is to simply hammer the surface to tighten it up and close any voids. Even if I have to to fuse additional metal onto the area I'll often hammer it a bit before finishing -- just in case. I have no experience TIG welding copper, so there may be fundamental differences I don't see. If the problem is just appearances and the "pinholes" are clean, this may help.