Quote:
Originally Posted by Diesel911
Isn't that the main ingredient in a lot of Rust Converters?
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Yes and it does more than etch the surface. It converts the iron oxide to iron phosphate which is hard and black. Naval Jelly is a product based on this chemistry.
Ketchup would have Malic and Citric acid from the tomatoes, but in manufacture various other acids may be added. Could be acetic or tartaric (vinegar) and so on. But no Phosphoric. So chemistry is different and the hard phosphate will not be formed. However, Coke would work if you can keep it where you want it! Maybe they should sell it in Gel form! Maybe mix Coke and Ketchup? Probably more expensive than buying a proper rust converter.
It's fun to experiment, but after cleaning the rust off by whatever method, I would still wash it down thoroughly and coat with a rust encapsulator like POR-15 (or DOM-16 which is much cheaper, at least here in Canada at NAPA)
I have used a lot of DOM-16 in trying to slow down the rust on my W123. It's about same as POR-15. Mostly I didn't use a rust converter, but it's not a bad idea.