Watching a lot of Wheeler Dealer episodes lately and saw Edd treating a rusted area with some solution . The product he talked about was "Rust remedy" (from Loctite; after googling). The rusted area is cleaned with sand paper and cloth and the grey liquid is applied with a brush and left for a few minutes. The rust gets converted chemically to another form and turns black. There are many similar products available in market ( many on ebay and amazon also) which basically does the same thing.
Here is how the stuff works:
http://events.nace.org/library/corrosion/MetalCoatings/rust-converter.asp
Quoting from the article:
"Rust Conversion Mechanism
The tannin is the heart of a rust converter. It reacts with the iron oxide, converting it to iron tannate, a stable blue/black corrosion product. Tannins are a group of water- and alcohol-soluble natural products extracted from a variety of plants. Little is known about their true structure as they are complex and variable. Industrial research in the effectiveness of tannin solutions as rust primers began in the 1950s. Since then, tannic acid (a tannin) has become a standard conservation treatment for corroded iron artifacts found on archeological sites."
(picture courtesy: Amazon)
Here is how the stuff works:
http://events.nace.org/library/corrosion/MetalCoatings/rust-converter.asp
Quoting from the article:
"Rust Conversion Mechanism
The tannin is the heart of a rust converter. It reacts with the iron oxide, converting it to iron tannate, a stable blue/black corrosion product. Tannins are a group of water- and alcohol-soluble natural products extracted from a variety of plants. Little is known about their true structure as they are complex and variable. Industrial research in the effectiveness of tannin solutions as rust primers began in the 1950s. Since then, tannic acid (a tannin) has become a standard conservation treatment for corroded iron artifacts found on archeological sites."
