Opinions requested: Rust or stain on frame?

[Kestrel4k]

Originally Posted by RHScott

Ah yes, complete disagreement as usual.

I disagree with your assessment, lol.

[Wakko]

Just hard chrome it and you don't have to worry about it. Duh.

[ORN197]

Originally Posted by Dan13

A parkerized finish provides no protection whatsoever against the metal below rusting. It is simply a finish designed to hold oil in place better than bare metal. It is the oil that protects against rusting, not the finish.

Originally Posted by Fenris_Bane

If it is rust, then the "protective parkerized finish" has failed and allowed the surface to start rusting. Cold bluing and "browning" are both "rusting" systems. Parkerized is a thin coating on the metal to help prevent rusting, but does not provide any real damage protection, like scratches. So if it is rusting, the Parkerizing is gone or so thin it grants no protection.

Actually, neither of these is entirely correct. Parkerizing... really, phosphating... is what we call a "conversion coating" process wherein some of the free iron on the surface of the part being treated is converted into a hard, inert substance with a distinct microcrystalline structure. This structure does provide a high degree of both mechanical and chemical protection in-and-of itself, but it is also somewhat "porous" with tiny gaps in the crystalline structure which can lead all the way down to bare steel. It's important to understand, however, that it's not just a substance sitting "on top of" the metal substrate. Most modern phosphate processes include some kind of final sealing step, where a chemical sealer is applied to the parts to attempt to "fill" the tiny gaps in the phosphate; in the old days they used different flavors of chromates, but now other products are used. However for maximum corrosion protection, Dan is correct in that the slightly porous nature of the coating does lend itself well to holding on to oil or grease (or paint, for that matter). But, obviously, over time that oil or grease can get washed out, if it was even applied in the first place. A little bit of freckling or what we called "blush rust" usually wasn't considered a big deal as long as the "active" corrosion was arrested, usually by painting the part. There's endless debate on internet forums about how to stop "active" corrosion but the bottom line is that if you deny it oxygen, you'll stop it. A little bit of oil (or paint if that's what the process called for) is really good at stopping oxygen from reaching the corrosion sites.

Among other duties I was a manufacturing engineer overseeing an industrial zinc phosphating line for a while.

[ORN197]

Originally Posted by Fenris_Bane

Interesting read. I was not sure how Parkerizing worked in a technical sense. I just heard that it can cause clearance issues because it adds thickness which can cause problems on threads and pin holes.

Ideally, if the baths are set up correctly, and the if rest of the process parameters are in control, you shouldn’t see many size/fit issues. But those are big “if’s”especially in an industrial setting. The amount of free iron stripped off the surface is very small… we’re talking maybe a couple ten-thousandths of an inch (.0002”) at most, and often not evenly (if you looked at it under extremely high magnification). The “coating” structure which then grows on the surface ideally would be about the same, so really no net loss or growth. But you will see a change in surface finish, that’s almost unavoidable. Various phosphate formulas are designed for different amounts of coating deposition, too; for instance the zinc phosphate line I ran was designed primarily to be a pre-paint treatment so the formula we used was considered “light weight”. The formula used for say a military firearms manganese phosphate, which is intended to be followed up with an oil treatment, would necessarily be “heavier”. On our line, the most common process control issue we saw was too much free acid content, which resulted a little too much stripping and not enough coating build, i.e. too thin, and excessive blush-rusting after treatment on parts that had a rough surface finish to begin with. Still it was barely measurable using regular instruments… a ten-thousandths loss at most. I can’t ever remember having a thread fit issue we could trace back to the phosphate process, but like I said ours was a fairly light coating. I’m sure it’s possible with a heavier/more aggressive line.

It was kind of fun to mess with and yes, I did use it for my own g-jobs every so often!

[Fogtripper]

Much of it looks like dried preservative. I agree with those suggesting mineral spirits, and perhaps leaving in the sun for a while to warm them up like a stock. Would definitely not jump into believing it rust before treating it like preservative.

[Pappy]

Try Big 45 Frontier Medal cleaner. Use with oil.

[bimmerman2010]

Hi all. Thank you for the input. Long story short, I tried in order Hoppes #9, then acetone, and finally the boiling in water conversion. Some spots have either completely vanished or diminished across the various methods, though the conversion bath was most effective it would seem. Spots are still present, but I believe it won’t be an issue as I’ll keep a light coat of mpro 7 oil on it. After all this, I am fairly certain the spots are rust discoloration that has been addressed at the current time. Once again, thank you to all for the input.