Also, it seems to me the term etching implies an acid based bath or "picling" agent to destroy any oxidised particles? Like using flux in soldering or brazing?
Lifted from Vantaaj's other sticky on paints http://www.alfabb.com/bb/forums/167187-post1.html
Etching or Direct to Metal
Some paints are direct to metal, some are not and require a primer. DTM paints have a small amount of acid in them to etch the metal they are applied to form a chemical bond to the underlying metal. Make sure you know which you have. If you spray a non DTM paint directly on metal, it will flake off, and conversely some DTM paints will blister most primers. Self etching and DTM are the same thing.
A lot of great information on this board. Just not enough hours in the day to read it all.
'73 GTV - '78 Alfetta Sprint Veloce - '88 Milano Verde