How does one know if something's active rust?

[Pack line]

If you plan on sanding red rust is much softer than black rust. I personally don't mind that blued look of black rust so I generally just brass brush the loose stuff off, degrease and into boiling water. Steel wool, oil and back to honing. But if i was going to do a restoration, sand, polish and all, no boiling water just straight to sanding.
There is a product called evaporust, i have not used it on a razor yet but it works great on everything else i have used it on. Leaves an acid etched type finish that comes of pretty easily. Acids do kill the edge. I have had some luck, with knives, nail polishing the edge first to protect the bevel from the acid.

 

[kayvee]

The second is etching the blade in phosphoric acid

Is vinegar usable as well? If so at what level of dilution and for how long can one dip a carbon razor in acid.

If someone has it, I'd also appreciate a picture of a razor that requires treatment with acid. I suspect I am overthinking it and looking to use acid wherever I see black on a razor. Which I probably shouldn't...

 

[Darth Scandalous]

Is vinegar usable as well? If so at what level of dilution and for how long can one dip a carbon razor in acid.

If someone has it, I'd also appreciate a picture of a razor that requires treatment with acid. I suspect I am overthinking it and looking to use acid wherever I see black on a razor. Which I probably shouldn't...

Vinegar can help remove red rust, I believe it converts it to a compound that is easier to scrub off. BUT. It will also leave a grayish patina on the good steel. The effect is more pronounced the longer you leave it.

I don't believe vinegar will react with the black oxide-- it might, I haven't tried it.

This is the sort of thing you should experiment with on a garbage blade before messing up a nice one.

 

[J B Addis]

Is vinegar usable as well? If so at what level of dilution and for how long can one dip a carbon razor in acid.

If someone has it, I'd also appreciate a picture of a razor that requires treatment with acid. I suspect I am overthinking it and looking to use acid wherever I see black on a razor. Which I probably shouldn't...

Vinegar (acetic acid) will remove rust, but unlike phosphoric acid which leaves the coating of iron phosphate behind, it leaves a raw surface that almost always flash rusts after being removed from the solution, which isn't a big deal if you're refinishing the whole surface afterward, but if any pits are left, there will tend to be rust at the bottom once again in short order, sort of defeating the purpose.

 

[Pack line]

Vinegar will remove most kinds of iron oxide. I've used it to remove mill scale from hot rolded steel to save my abrasives. I like to neutralize with baking soda after.

 

[kayvee]

How do I know when I’m done with phosphoric acid treatment?