Acid Dipping Engines

[spewey at comcast.net (Spewey)]

But seriously, folks...

naval jelly is an acidic jelly because painting/wiping (without dipping) 
syrupy acid onto an irregular surface would create a lot of hazardous 
droplets.

Acid eats the rust like this:

Fe2O3 + Fe + 6HCl ---> 3FeCl2 + 3H2O

See that second Fe?  That's good metal!  One of the links I found was of 
a Camaro race series where a protest was lodged against a team that acid 
dipped the roof (to lose weight) and vinyl-covered it to disguise the 
pitting.  Paging Danica Patrick....

Base (lye) doesn't eat good metal but the hot-tanking process probably 
involves Zinc.  The rest is done by pure soapyness:

"Since Zinc likes to bond to things better than Iron (Fe) the Zn+ 
molecule attacks the rust and takes the Iron molecule off and bonds 
itself to the Oxygen molecules that made up the rust. BUT in doing so it 
winds up floating in the solution. The result, the rust gets stripped 
off the Iron part, the Iron itself is untouched. This type of process 
has absolutely no bad effects to the original part just to the rust on 
the part."
http://www.btc-bci.com/~billben/rust.htm

Dude who uses lye (+Zn) at home to clean old guns, etc.:
http://www.civilwaroutpost.com/Ironrelics.htm

Dude who says use vinegar (an acid) first for rust but no Zn:
http://www.griswoldandwagner.com/cleaning/cleaning.html

POR-15 is a diisocyanate.  Everybody's got their own view:

"Isocyanates, together with related compounds such as cyanogens and 
cyanamides, are chemicals of the cyanide and nitril class, which contain 
the CN group.... Harming the human body, Isocyanates can essentially 
damage the plasma and internal cell membranes."
http://www.stovebolt.com/techtips/rust/zerorust/zerorust.htm#isocyanates

Picklex doesn't have an msds available (they must in order to ship it) 
but it says it's an ortho-ester.  Hmmm, dunno.