My experience with Phosphoric Acid is similar, but different! This chemical comes under many different labels/names. A couple very old ones are Naval Jelly and Ospho. Both of these older materials are designed to be wiped on, sprayed on, or brushed on, but not soaked in. I'm not really sure that soaking a piece of metal in Phos Acid for extended periods is a good idea, but I'm no Chemist. Ospho, for example, is like water. You apply it to your piece and let it dry. You don't wash it off. In 24 hours you come back to it and check it. If there is a white, powdery residue then there is still rust remaining, and you apply the material again to the affected areas. You are supposed to repeat those steps until the white powder is gone, hence no more rust. The rust converts to carbon (?) and the metal is sealed. You won't have flash rust, but the coating doesn't last forever. At this point, you wire brush any powdery residue, use a self-etching primer, and paint. Bullet-proof!
POR-15 has a good product called Metal Ready. It is also Phos Acid, but it conatins Zinc too. The Zinc provides a "cold dip" giving an additional layer of rust inhibitor. The significant difference in application between POR's brand and straight Phos Acid is that POR's brand requires you keep the metal wet for 20 minutes, whereas with Phos Acid you just spray and walk away.
Don't pour these materials into a metal container to apply. Use only plastic containers.
Your pictures are great, and no criticisms intended.
Go Fish! <*////><
But the right word at the right time... "Hey, give me a little hug!" That's the difference between lightning and a harmless lightning bug!