evaporust

[coxy]

g'day all
just a quick question for anyone who has used this
does this product leave a black carbon deposit after use and does that just wipe off? also are there different brands and what is the best one cheers

[slawsonb]

I am an evaporust fan. My weapon of choice against rust. Yes it leaves a black residue (mostly carbon from the rust/steel), but it can be easily removed with a stainless or brass brush or in some cases a damp cloth (dry immediately after wiping). In some cases the black will be on the surface of rust that has not been removed completely (too thick for only one soaking). That is why I prefer using a brush. As you remove the black, any remaining rust will show as the red rusty color it started as. Just keep soaking until it's all gone...
...bert

[BS Mechanic]

I'm not sure about the exact names, but there are several closely related oxides of iron, both red and black are oxides.  The red stuff is the "rust" that forms on the inside of your gas tank, as it eats holes in the steel.  It's hard to get off the steel, promotes more rust, and doesn't support paint very well.  The black stuff is typically what the various rust converters make out of the red rust.  It can be fairly easily washed or brushed off, and once removed, whatever remains provides good adhesion for primer or paint. 

Maybe someone can speak with more detail?