I have a small spot of rust on the bottom side of my steel frame's top tube (Columbus Niobium tubing). It's from abrasion during transport that I didn't notice until it was too late. The spot is about 2cm x 2cm and most the worn area is white in colour (base coat or primer?) but there's a bit of rust forming in the center.
I'm not ready to get the frame totally repainted so what's the best way to get this patched up?