Originally Posted by
seankanary
When I finish a fillet, some areas have a really dark(almost black) area around the joint. It is sparse and usually outside of some of the fluxed area. How does one prevent that from happening?
It's not likely that you can get rid of it. It's carbon precipitation, and if it's outside the fluxed area there is little you can do other than use less heat. It's happening under the flux too, but the flux carries the carbon away from the joint. Gas fluxer seems to help with this, not that it matters.