Just finished sorting a screw bin with lots of rusty stuff in it including brass screws that somehow had surface rust on them when in the same bin and adjacent to a rusty screw. Have had aluminum plate that became pock marked with a coating of rust when it spent time toucing a rusting steel plate. Rust tends to spread to other surfaces in even an air born way once it's introduced to an area where there is none. So what is rust anyway? Is it some form of metal eating virus, some form of decomposition of the metal caused by what is in the metal or is it something other than what the metal is made up of as if some form or termites? How is it that you can remove rust by way of DC current, yet batteries that get old tend to rust when the acid leaches thru the container? How is it that high temperatures tend to rust un-treated metal in an expediated way at times over that of metals that got and stayed moist? This all at times no matter what type of metal or surface treatment is in use.