Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
first off, it's nothing to worry about. It isn't going to get worse, so you can just leave it for the last step before paint. In fact, you can usually wipe it off with a wet rag.
I have found that if I leave something soaking in hot water for as little time as it takes to get rid of the flux, I generally don't get rust. Actually, removing rust is one of the things that flux does. If I'm lazy and leave something overnight or longer, I get rust. I'm sure there are ways of avoiding rust chemically, but I'm not sure it's worth it. In hot water, silver flux comes off quickly, the better bronze fluxes take a little longer. If you are going to leave a frame unpainted for a year, then you might want to use one of the corrosion prevention chemicals, paint places have them. Check with your painter first though.