Do you force patina your metal?

Good morning Permies!

I have a question for everyone when it comes to things that are bare steel.

How do you protect it?

I have read about forcing patinas, and I'm thinking about doing it for a piece of 1/4 steel plate that I'm going to use for an anvil so I can metal stamp some tags for my gardening.

Three different levels of patina on metal.

I also have some carbon steel knives that if I like the results I may try it with them.

What are your thoughts?

I'll be experimenting here hopefully tonight so I might reply with my results.

Hi Tim;
Automotive clear coat spray paint is my suggestion.

I haven't tried it yet, but automotive restoration guys will clear off the worst of the surface rust and then paint with phosophoric acid. This apparently converts the aggressive, destructive rust into a more stable form of iron oxide (of which there are many).

Douglas Alpenstock wrote:I haven't tried it yet, but automotive restoration guys will clear off the worst of the surface rust and then paint with phosophoric acid. This apparently converts the aggressive, destructive rust into a more stable form of iron oxide (of which there are many).

You can look up "browning" like in gun barrels and actions, but this always requires oil over the browning.  

There is LPS sprays,  1, 2 and 3 versions, (#3 almost is waxy like)  for short, medium and long term protections of your metal with none of them just staying put if you are pounding on the metal, like it sounds like you might be.  A can goes a long ways, and I would be tempted to use #1 or 2. clean metal quickly, use and then recoat.  None of the hard coats, will allow the "clean quickly" part happen.

I have "forced patina's" for many years, and I don't know any of them that would Just "stay protected with a one time treatment" without oil  or wax of some type. Generally wax,  this keeps oxygen from getting to the metal.

Maybe, just maybe  a SPF 50 treatment, would last the longest.. we use on airframe building, but then again, we don't hammer on it.

If you use the phos. treatment, I am doubting you would want to apply full strength liberally,  it will brown before your very eyes, but can continue to work if you don't neutralize,  Which takes you right back to the nice browning,  but you have still protect it.  (WAX, OIL, ext.)

Guess I haven't helped much, but the point I was trying to make, is that it is pretty easy to protect, much harder to protect and still use and abuse.

I’d guess phosophoric acid reacts to make iron phosphate, (probably with some amount of oxides remaining in there as well).

There are many possible ways. The 2 mentioned above are good. Here’s 3 more.

1) Zinc galvanizing, or electroplating zinc or other appropriate metal.

2) Wax dissolved in naphtha paint thinner and applied.

3) Anodizing to magnetite. (The material of the black grains in beach sand).  

Constant voltage technique is used to form oxide films on mild steel alloys in potassium hydroxide (KOH) electrolyte as a function of the anodization voltage of (1-6V), concentration of (40-70Vol. %), temperature of (20-100°C) (68-212 °F) and anodization time of (5-75 min).

The space between two electrodes was (50mm) (2”). The ratio of steel anode (+ electrode) to cathode area (- electrode) was (1:5). [I’m guessing these parameters aren’t critical.]

Optimum conditions for anodizing mild steel alloy are: (1V, 40Vol.% KOH solution, 20°C, and duration 5 min).
Current density was 45 mA/cm2.

In the range of anodizing conditions, the thickness of anodic oxide film is increased in the order by these factors:
Temperature > voltage > time > KOH concentration.

Remaining surface porosity can be sealed by different methods like boiling water, or nickel acetate  solutions to further improve the corrosion resistance.

Source:
https://www.iasj.net/iasj/download/80e2b0e7361a5c8d

I forced a patina on my carbon steel cleaver and paring knife. I just used lemon juice. The knives are stored right now, not used, and the patina has held up pretty well. But it has been four years and I should probably redo it.

From my experience, I don't think a lemon juice patina would hold up to the weather very well.

There’s a good summary here:
https://en.m.wikipedia.org/wiki/Bluing_(steel)

Jeremy VanGelder wrote:I forced a patina on my carbon steel cleaver and paring knife. I just used lemon juice. The knives are stored right now, not used, and the patina has held up pretty well. But it has been four years and I should probably redo it.

From my experience, I don't think a lemon juice patina would hold up to the weather very well.

I recall reading that sticking the blade in a big raw potato will do the same thing.

I decided to give a force patina a try, even though I now am thinking of going a waxed route to protect the steel due to the nature of its intended use as pointed out by another commenter.

I was on the fence watching the slow reaction, I did flip the steel twice and left marks by accident from my fingerprints.

I was underwhelmed in the end. I am going to do a bit more research on 'at-home' patinas but I'm going to look at the commercial stuff to get inspiration towards the process.

Wait, what, you didn't etch a pattern in there? Hello Permies perhaps?

Mike Philips wrote:I’d guess phosophoric acid reacts to make iron phosphate, (probably with some amount of oxides remaining in there as well).

Interesting, thanks -- I hadn't looked up the chemistry. I have no idea how stable the resulting compound might be when exposed to atmosphere, since the car guys just want to stabilize any remaining rust and then seal it with primer.

Before phosphoric acid, the go-to was muriatic (hydrochloric) acid.