There are plenty of thin liquid convertors available.
http://www.eastwood.com/eastwood-ru...ode=ga110070&gclid=CNvIoaOejrMCFQkFnQod4VwAtg
Total Solutions 347 Convert Sprayable Rust Converter,4 Gallon/Case: Amazon.com: Industrial & Scientific
http://www.cmcchemical.com/featured/347_spryable_rust_converter.html
http://www.eastwood.com/eastwood-s-fast-etch.html?reltype=2&parent_id=5609
If you read the msds sheet on most rust convertors the main active ingrediant is phosphouric acid. The reaction between iron oxide and p acid is a black iron phosphate coating which is why most convertor brag about how their advance formula leaves behind an inert non rusting black coating when really it is a basic chemical reaction.
