Ive been experimenting with citric and oxalic acid to make a gel, first trial worked great, except it dries out fast. Of course it could be rewet and rebrushed easily. Trying a few other things to keep it wet longer and not effect the PH. My intention is to provide instructions on an acid mix that can be brushed on, you control the thickness, you control what acid type ( citric, oxalic, phosphoric) This would prevent the need to submerge parts in the mixture. I have visions of an acid gel we can shoot on the bottom of a car with an undercoating gun to derust frame and floors, power wash off and neutralize the underside.