Rust Removal

The archives contains an item by David Huffman on rust removal. It
is a very simple approach to cleaning up some neglected tools which
have become rusty. The process involves a sort of reverse plating
that turns rust into a black powder coating.

My question now is: What exactly is the black coating and how can it
be removed? Some can be wire brushed off, but not all. I tried a
quick dip in nitric acid which removed some, but it is a pretty
drastic approach. It would be nice to end up with bright metal and
no residue. Any suggestions?

Herb McQuarrie

Rust removal is best effected by immersion in a solution of water and
hydrochloric ( muriatic) acid. Always pour acid into water. never
pour water into acid. Make sure that the item to be cleaned is free
of oil. wash it in detergent if need be) Leave the object in the
solution until all rust is gone. Nitric acid is used for copper and
brass. Again, a dilute solution will do the trick. but, never leave
brass in nitric for too long or it will eat out the zinc and you will
trash your object. Nitric is nasty stuff. it loves to munch on
clothing much as does sulfuric. If you get it on your skin it will
leave an ugly brown stain. If you get it in your eyes you can kiss
your sight goodbye ! Hydrochloric acid is readily available in the
’States at hardware stores and sometimes at grocery stores in the
pool supplies section. Buy a pair of plastic gloves while you’re at
it. Use baking soda to neutralize spills. Ron Mills, Mills Gem Co. Los Osos, Ca.

    My question now is: What exactly is the black coating and how
can it be removed? Herb McQuarrie 

Hello Herb; I’d suggest that before you begin the stripping
operation, you physically remove as much loose rust as possible with
a wire brush. Strip the article for a while, then rinse and wire
brush, then continue stripping. As far as I know, the black coating
is another form or iron oxide, but one that does not bond as tightly
to the iron as the red variety. I’m never sure of the chemistry,
ferric oxide, ferrous oxide, etc. Perhaps some of our resident
chemists can help.

David L. Huffman