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Clooney: I first found phosphoric acid etchant at NAPA, back around 1980. I had to treat some metal that had been in a fire, and this even said for burned metal on the label. I used to use Metal Prep, but when I ran out of it a few months back, I saw a product at Discount Auto Parts called "Right Stuff De-ruster Formula #3000". It seems to me to me be a bit thicker liquid, but still sprayable/brushable. About the consistency of dish soap. Maybe it hasn't been thinned with water. I use it after sandblasting to provide the last removal of rust in the pores, and it gives a nice little phosphated look, and the parts seem to stay rust free for months on the shelf. Here in Florida I fight humidity 12 months a year. I'm experimenting with electrolysis cleaning right now, and after the bath, I spray it on, wait a bit, hose it off, and the dry the part completely. This stuff runs about 8-9 bucks a gallon, and it goes a long way. Sometimes I even put in my old paint gun and just spray it on (USE A MASK !). The side benefit that you know is that it also removes the last vestiges of silica left imbedded in the metal. Left behind those little silica nodules draw moisture and cause paint and primer to "pop". They have a website = http://www.cli-rightstuff.com I'll post the link below. I like it as well as anything else I've tries, and since it is available locally, I don't have to buy in bulk. Great for swishing old gas tanks, too. Locks up the old red rust and converts it to the stable form of iron oxide (black oxide). Here's a note I found elsewhere: Rust is really Fe2O3, a reddish form of iron oxide. Iron has another oxide, Fe3O4, which is sometimes called black oxide, black rust, or hammerscale. Black oxide is a good protection for steel. Like aluminum oxide, black oxide molecules are the same size as iron molecules, so black oxide does not grow or flake. Black oxide is true gun bluing and the oxide found on some drill bits. Black oxide is also seen on iron and steel that has been hot-worked. I strongly advise folks to stay away from Muriatic acid, as all it will do is erode the base metal, and the iron chloride residual it leaves behind can remain corrosive after the paint is applied just waiting on a scratch to find mioisture ! Hope this info helps ! Frank 70D/855 Link
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