Most high quality rust removers are based on phosphoric acid as their active ingredient, up to 25% concentration. I usually buy the 85% phosphoric acid if i need it for something. Some of the rust removers come in a gel form to allow then to stick to the surface being cleaned instead of dripping off.
My question is this: what can i use to create rust removing gel using the 85% phosphoric acid as the base? I am thinking of some sort of soap or perhaps grease, but not sure about reactions that may happen between the phosphoric acid and the thickening agent, hence reducing effectiveness of the acid for rust removal.