intentionally making steel rust

May 4, 2007 8:55 AM

How can I make something I've fabricated out of cold rolled steel achieve a uniform patina of rust?

I'd like to avoid using anything toxic or nasty like muriatic acid. This doesn't need to be done quickly, it can sit for a couple of weeks.

posted by machaus to home & garden (19 answers total)

What's so nasty about muriatic acid? Your stomach is full of it; just dilute it 10 or 100 to one with cold water as you dispose of it and you should have no problems.

Anyway, rust is just oxidized iron; if I wanted to make something uniformly rusty, I'd lightly rough up the surface with fine-grit sandpaper and keep it a little moist (with a spray bottle or something) to facilitate the reaction. Actually this would be just as good as the acid, since the only point is to eliminate whatever protective coating the metal might have.
posted by rkent at 9:03 AM on May 4, 2007

Ideally you would have the part sandblasted to thoroughly remove any coating that is on the steel.

Leave it outside and spray it down with a hose occasionally if you don't get much rain where you are.

This should give you nice even brownish coat of rust - you'll have to coat it with something as the rust will come off on your hands or whatever touches it.
posted by davey_darling at 9:10 AM on May 4, 2007

you'll have to coat it with something as the rust will come off on your hands or whatever touches it.

I've read that this does a nice job of sealing it.
posted by machaus at 9:15 AM on May 4, 2007

I found a nice discussion about metal finishes online, which has a nifty-sounding trick using hydrogen peroxide (near the top of the page).
posted by aramaic at 9:33 AM on May 4, 2007

Some sort of agent that releases oxygen radicals should do it. Either hypochlorite (bleach) or hydrogen peroxide should work fine.
posted by Steven C. Den Beste at 10:03 AM on May 4, 2007

More... apply the bleach or peroxide with a spray bottle.
posted by Steven C. Den Beste at 10:04 AM on May 4, 2007

If you're really keen to stay away from "toxic or nasty" liquids then may I suggest salt water.
posted by alby at 10:16 AM on May 4, 2007

Ditto the sandblasting and salt water.
posted by Koko at 10:22 AM on May 4, 2007

Just a thought, but maybe emulate harsh outdoor conditions by repeatedly putting it into and them removing from your freezer.
posted by humblepigeon at 11:01 AM on May 4, 2007

If you want to do something a little different, but which I think might be incredibly elegant and interesting, you could try inoculating it with rust producing bacteria:

Some chemical reactions in which bacteria participate are harmful rather than helpful to industry. Bacteria are major agents of metal corrosion (wearing away) through the formation of rust, especially on metals containing iron. During the early stages of rust formation, hydrogen is produced, and it acts to slow the rusting process. However, certain bacteria use the hydrogen as a nutrient with the result that they greatly speed up rust formation.

To do this, I would find a small piece of old half-buried rusty metal outside, bring it in and scrub off some of the rust scale and create a suspension of rust, say with a blender, which I would then wipe onto my piece. You would need to use dechlorinated water (boiled or filtered) for every step in producing the inoculate in order to avoid killing the bacteria, and a cotton cloth instead of a paper towel for the same reason.
posted by jamjam at 12:27 PM on May 4, 2007

You could just mix up some salt water. Or apply a thick coat of 1980's Chrysler paint. That always worked well.
posted by kc0dxh at 12:49 PM on May 4, 2007 [2 favorites]

Salt water takes forever on its own, you need an oxidizer.
If you want uniform thick rust fast (like 5 minutes or less) Mix up a batch of the following, half hydrogen peroxide (drugstore grade is fine), half vinegar, and a pinch of salt. The reaction is uhm, rather fast, and seems to produce a gas of some sort (I'm going to guess hydrogen) Its worked well for me, just put on a spray lacquer when you are done to keep everything in place.
posted by Pink Fuzzy Bunny at 1:02 PM on May 4, 2007 [1 favorite]

Oh, and as for getting rid of any oxide that might already be on the steel, pop down to your local hardware/grocery store and pick up a can of PH-, its used for pools to reduce the PH of the water. It contains sodium bisulfate, which then disassociates in water to produce a 5% sulpheric acid mix, any left over sodium bisulfate will just precipitate out of solution. The acid will bond with the oxide, it happens faster if its slightly heated. Its the same stuff as jewellers pickle, just cheaper, and higher grade.
posted by Pink Fuzzy Bunny at 1:06 PM on May 4, 2007

My dad used to make a patina for his cast bronze sculptures out of eggs and orange juice. He'd mix 'em together and slather the resultant mess onto the sculpture and let it sit and dry in a sunny spot for a few weeks. He'd usually have to do multiple coatings, as the mix would tend to crackle and break apart like old paint after a few days.

It doesn't smell as bad as you might think.
posted by lekvar at 1:33 PM on May 4, 2007

Raising the temperature may help. Oxidation happens much faster at higher temperatures. When metal is being forged it'll often form rust immediately.

I use electrolysis to remove rust. I wonder if it would speed oxidation if you reversed the polarity of the electric charge? If so that would have the advantage of working on a pretty large scale (I have seen people remove rust from something as large as a trailer with electrolysis)
posted by RustyBrooks at 2:38 PM on May 4, 2007

Go to a gunshop and ask for some browning solution. It is made by Birchwood Casey.
posted by Raybun at 4:49 PM on May 4, 2007

I use electrolysis to remove rust. I wonder if it would speed oxidation if you reversed the polarity of the electric charge?

Yes, it would work perfectly. Just reverse the clamps. Make the piece you want to rust the anode instead of a sacrificial piece of steel.
posted by IronLizard at 6:21 PM on May 4, 2007

As an aside, muriatic (or hydrochloric) acid is a great REMOVE rust, not create it.
posted by IronLizard at 7:04 PM on May 4, 2007

Vinegar. Apply with a spray bottle.
posted by misterbrandt at 8:13 PM on May 6, 2007