I tried cold bluing an entire handgun, and didn't like the result at all (except on the small items like screws), so I decided to remove the bluing and start over with a slow rust-blue. I washed off the firearm with hot soapy water, then used Birchwood Casey Blue and Rust Remover, then Evaporust, and then naval jelly, then sanded down everywhere I could get to, but certain areas of certain parts where I can't get sandpaper onto well still have 100% bluing. What's going on? I know that cold blue is actually a silicon coating. Does that make it immune to all of those rust and blue removers? Is there some other chemical I need to use?

Try the old Lead Away cloth. That stuff will remove any bluing, hence the warning never to use it on a blued firearm.

I use a cheap soda blaster from Harbor Freight with my cheap Harbor Freight compressor. But then I only tinker on my own toys.

Cold blue is a selenium compound (Copper selenide is what you see on the steel) and should be able to be removed by any acid. Why the Birchwood Casey stuff, which is a mix of several acids, didn't work right off is indeed a mystery. What cold blue did you use? I would clean with a powerful degreaser like acetone or brake cleaner and try the Birchwood Casey stuff again. Stuff not intended for gun work can lead to problems like Naval Jelly being phosphoric acid based leaving iron phosphate. An acid like the B-C product should fix that.

I used Brownell's Ox-Pho Blue Liquid and Ox-Pho Blue Creme. Thanks for the tip on the naval jelly. It didn't seem all that effective any way. I misstated the order, BTW, I used the naval jelly before the Evapo Rust, so maybe things will be all right, but I'll rehit those areas with the B-C Blue & Rust Remover.

Vinegar (acetic acid) removes rust and blue

The acid that they have in the pool section will take it all off.

It's cheap too.

And etch metal. If you've used it (hydrochloric acid) to clean steel before welding you'll know that even diluted down quite a lot it leaves frosted metal from the etching - very reactive stuff.The old gunsmithing books advise sulfuric acid - diluted down quite a bit. The Birchwood Casey stuff has that plus phosphoric acid and a touch of oxalic acid all diluted down and ready to go.

I have heard muratic acid will remove bluing, but I've never tried it.

I used liquid case cleaner, it removes everything.

After another application of B C Rust and Blue remover and scrubbing hard with a plastic bristle brush, some more came off but there is still plenty of it in the threads of the ejector rod and also in the knurled end. It seems like it is more the shape of the surface that affects whether I can get the blue off. Anyway, I plan to move on and try to rust blue over these few areas that still have cold blue on them.

ospho rust remover will turn it white on contact

Very strange, the sulfuric acid in the BC should eat the cold blue immediately. Sounds like there's some kind of coating over the blue. Tried acetone or lacquer thinner firat?

I had to remove factory bluing once in preparation for browning a TC Hawken barrel. I started off with a wipe-down with brake cleaner outside. I used rubber gloves and safety goggles.

I didn't know what I was doing, but I guessed that HCL (Muratic Acid) would do the job. I used a plastic hard-side gun case with the foam removed.

On one side, I mixed hot water and sodium bicarb (hot to get it to dissolve faster). It was room temp by the time I started. In the other side, I used plain cold water.

I plugged the barrel at both ends and placed it in the cold water and then began adding HCL slowly. It didn't take long. All of a sudden the bluing just vanished-- poof! I reached in and pulled out the barrel and stuck it in the sodium bicarb. After 5 minutes, I rinsed in cold water.

I'm not saying this is the best way, or even a good way. It worked, and the resulting browning job has lasted over 20 years.

I use acid in my blueing operation

The bathroom cleaner CLR will do the trick.