Bill DeShivs said:
Walt- most cold blues-including Oxpho Blue electrolessly plate a thin, porous layer of blackened copper sulfide on to the metal. This colors the metal, but it is not a controlled form of rusting. Most cold blues seem to PROMOTE rusting, rather than prevent it.
You may be correct, and I'm certainly not any sort of a chemist, but Oxypho Blue appears to be a bit different than some of the other Cold Blues and doesn't seem to be primarily copper sulfide. There is a little copper in the solution.
The bottle says OxyPho Blue, "contains Phosphoric and Selenious Acid, Cupric and Nickel Sulfate." Those items are typically listed in the order of volume with the biggest volume listed first, on down to the least. If that's the case,
things other than copper (or a version of copper sulfate, if that's what is in there) make up most of what's in the bottle.
Wikipedia says that Phosphoric acid is a rust inhibiter (but doesn't explain how it does that); it also says that Selenious acid is used to color metal. That same source says that Cupric (which is a form of copper) resists water and forms a
rust-like coating;
copper is also used as an antidote for Phosphoric acid poisoning -- which may explain it's presence in the OxyPho Blue mix. I can't find much about nickel sulfate or what it does, but because in most forms it's blue, it may also be a coloring agent. Copper sulfate is the third ingredient listed, so OxyPho Blue is clearly not mostly copper sulfate.
In steel when the surface oxidizes, the result is called rust. With copper, oxidation's result is called verdigris. If a cold-blued gun "rusts" after being treated by a particular cold bluing solution, what you see could be verdigris or it could be that the bluing solution was not properly applied. As I said, I'm not a chemist (or metallurgist), but don't see how cold bluing would CAUSE rusting.
I've never had problems with OxyPho-blued guns rusting, but will agree that the finish is somewhat porous; all cold blue makers tell you to keep the finishes oiled. I just use BreakFree CLP, and that seems to do the job.
Some cold blues, when applied, do sometimes cause spectacular reactions that look like rust when first applied, but I've never seen that with OxyPho Blue. That may be because the application process include applying multiple coats, but always wiping it dry with a soft cloth and and burnishing the finish with very fine steel wool between applications.
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