while I'm at it--electrolysis and flash rust

Just because I'm experimenting with Phosphoric acid doesn't mean I've given up on electrolysis. I put 2 very rusty andirons in the vat last night. This AM--black. Hosed off with garden hose and sat in hot sun. Flash Rust. Kinda hard to prevent it when the rust removal process required the item to be in water. I'll probably just paint over it but curious what others do in this situation.
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Flash rust is a consideration when sandblasting, have to get that primer coat on fast, more so if its humid. For those, hard to figure why you don't just wire wheel/brush them, then prime and paint, I would not paint over any rust if possible.

Years ago someone told me to use muriatic acid. Well that was a disaster !
Went back to sandblasting everything I could unbolt or would be COMPLETELY disassembled and cleaned.
I have never really had an issue with sandblasted parts rusting as long as I keep them inside after done.

Kinda hard for me to figure out how to get a grinder with a wire brush to all the surfaces in that scroll work. And just a hand wire brush would never have removed all the rust--it wouldn't come anywhere near as clean as this is with the flash rust.

Normally I sand blast everything I am going to paint and then spray it with the stuff in the link below. Turns your metal black, takes 24 hours to dry before top coat and I have used it for years and have some items laying around my shop for 3+ years now that I have yet to paint, but no rust. I live in Iowa so we do have high humidity around here.

Have used Muriatic acid before too, but I only use it to remove the galvanizing off NEW bolts before I paint them.
Anti Rust

I was thinking after you used a primary means to remove the initial rust, the slight rust that can occur from humidity, moisture, or whatever conditions are right for it to happen, that is what I call flash rust. It is easy to remove at that point, unlike the initial rust, mill scale or latence that is on the steel before you start which we all know can be so darned difficult LOL ! + the fact that its so easy for it to repeat unless you get to clean steel, get all the pits or treat it. Funny how some steel will just surface rust, discolor, show a patina, but no scale flakes, pieces or heavy pitting, will occur. Some steel just flakes of, rust flakes enlarge and create forces that can literally crack a heavy truck frame rail. I used to drive a '74 DM Mack tandem sileage body for a farmer friend, and the double frame had been rusting in between it cracked the frame and had to be repaired more than once over the years. Mechanic said if you see that happening, knock off the rust and keep it from building up, steel wants to expand 3x its size when rusting heavily. I never thought it could do that to a Mack truck frame rail though.

I just replaced a fuel tank in a '96 cobra mustang, inside had a scale build up, not so much rust or even pitting, but the outside was still mill or raw finish, as it came from the factory. I got something, on part of the exterior and it flash rusted immediately. The tank would clean up and could be used with no problem, but like the subject of your post, I'm no expert on chemical applications, corrosives or even electrolysis, so I put it aside for future reference, as its original to the car as well, new one was a perfect fit and match, but did have a finish coat on the outside. That flash rust area was immediate, but cleaned up very easily.

It seems a simple yet complicated process--dealing with rust. Complicated further by the expected use of the item, time, and money you have to put into the problem.

The trailer in my previous post is for me but I have no spare money and but I have an hour now and then for a year if necessary to get it done--one reason I like electrolysis where a few minutes submerging it and turning on the power and I can walk off while magic happens--but the trailer is too big.

The andirons were rusty and I'm selling for a friend. Rusty they drew no interest. Hook them up, drop them in the tank, dry them off, give them a coat of flat black and perhaps I can get people interested--thought process anyway. I can't put much effort or money into it or I might as well be giving them away.

I try to learn doing this stuff and I thought I'd see how others that used electrolysis handles flash rust. Like I think I said it seems quite logical that it'd be kinda hard taking steel out of a water solution and drying it fast enough it doesn't rust a tad.

Oxyacetylene torch set to a slightly oxidizing flame, sweep it back and forth over the object slowly enough for a slight color change, not long enough to warp or distort.

Sometimes this is appropriate, sometimes it's not. Depends on the piece and where it is.

Anything ferrous that comes out of a corrosive bath (including any impure water) gets dried immediately- fan, hot air, blown dry... If the metal is cold you have to hold the heat on long enough to get past the combustion products (water) condensing on it.

I used to own a weld/machine shop and flash rust was "not allowed." Give it a quick oxidation layer that is not the red rust and you're good until primer and paint day.

I am not much of a painter but on occasion I had to deal with metal that developed a quick rust and my simple cure was to rub the rust area with a rag soaked in paint thinner and then paint with the primer.

When I did my parts I used Picklex 20 to prevent flash rusting prior to painting.