Etching wrought iron

[Mtbarn]

I have a piece of wrought iron that I’ve finally found a project worthy of. 

I want to etch the wrought to show off the grain. Any experience with etching wrought?

[Chris C]

I've never needed to etch wrought iron, but I've read that Sodium Bi-sulfate, the same chemical used for swimming pools, is a very aggressive etchant.

[Steve Shimanek]

Circuit board etchant/ferric chloride is commonly used; Radio Shack used to carry it.

[anvil]

Even plain vinegar will work. No matter what you use, make sure you neutralize the acid when done

 

 

[Mtbarn]

Would tap water with baking soda work as a neutralizing agent?

[SLAG]

Mr. Mtbarn,

Sodium bisulfate is acidic so a base chemical will neutralize it.

So baking soda will work.

SLAG.

[anvil]

yes, on baking soda

another easy to obtain acid is muriatic acid. most hardware stores have it. Its used for many things

[Mtbarn]

Thanks for the replies. I’ll post a picture soon. 

[ThomasPowers]

Note that the grade of refinement makes a big deal on how etched WI looks.

[George N. M.]

Muriatic acid is a name for diluted hydrochloric acid (HCl).  It comes in various concentrations such as 14%, 29%, and 31%. Sodium bisulfate is NaHSO4 and is made by the partial neutralization of sulfuric acid (H2SO4).

"By hammer and hand all arts do stand."

[anvil]

thanks, George. Good info. I should of picked up on that. I'm not familiar with sodium bisulfate. I have used sulfuric acid and a few dilutions of hydrochloric acid.

[Donal Harris]

I wonder how it went?

I have a pool, so muratic acid is something I always have on hand, but am not sure I would want to use it for etching, especially if it was just a one-off thing. It isn’t extremely dangerous, but it can be.  Neutralizing it isn’t all that easy and you can’t just dump it in the yard or down the drain.

 

What about vinegar and hydrogen peroxide?  Mixing them produces peracetic acid, which isn’t 100% safe.  It will burn your eyes and lungs if you breath the vapors, but not nearly as badly or as easily as muratic acid can. You can add NaCl to speed up the reaction.  I am not sure what purpose the salt has.  I assume as a catalyst.

You can also add NaCl to just vinegar alone, but I have never tried it.

 

[Frosty]

Yes, muriatic (hydrochloric) acid is a haz mat and requires proper PPE and procedures to use safely. I don't understand a difficulty neutralizing it though, it's a pretty standard practice for acid, Dilute then add a suitable base, typically baking soda.

Various combinations of: vinegar, peroxide and salt are pretty standard for patination. Salt is corrosive. 

I got some neat colors on copper with garlic but couldn't reproduce them with any degree of reliability. <sigh> 

Frosty The Lucky.

[ThomasPowers]

I used to have a limestone gravel drive way that was handy for neutralizing acids which helped keep the weeds down too.

[Donal Harris]

How long would it take the gravel to stop smoking?

I experimented with four small pieces of WI yesterday. Two hours in muratic acid made it so you could you could see a difference in coloring and direction of the grain, but didn’t make the texture different. Three hours in a mixture of vinegar, H2O2, and NaCl seemed to etch much more aggressively. The grain was apparent to both the eyes and touch. 
 

My trial also made another thing horribly apparent. My skills at forging stink. Cracks which were not visible before etching were clearly visible. Spots where I had let the iron twist under the hammer were also obvious. I also learned texturing that may look nice in mild steel are not so nice in etched WI. 

[ThomasPowers]

I'm cheap; by the time the acid got to the gravel it didn't smoke much at all!  It did leave rust stains though; glad I didn't live in a fancy neighborhood with HOA & Covenants to deal with!

[Donal Harris]

I have never had to deal with an HOA. Our last house would have been the first, but we sold it before it started. The development had to reach a certain percentage of completion before it would begin. Our back neighbor would have certainly been at its head. She was a nightmare. 
 

My problem with neutralization is mainly container size. 

[Donal Harris]

I tried 1 part pool muratic acid in 2 parts 3% H2O2. It works much more aggressively than muratic acid alone. I expected adding the H2O2 as an oxidizing agent would speed up the reaction, but didn’t realize it would be night and day faster. 
 

36 hours in muratic acid alone only etched it enough that I could see the structure as dark and light gray bands, but I couldn’t really feel them. Two hours led the pieces looking like weathered wood.
 

The first piece was just a short piece of rusty WI that hadn’t seen a hammer since 1860 or so. It was the frame around the bars in the window. I really like the texture the etching gave  

 

The second piece is a piece of one of the bars from that window.  I had flattened it a bit and it was no longer rusty. You can see and feel the grain in the WI, but not nearly as much as in the 1st piece. Perhaps 3 hours or 4 hours would have made the etch deeper. 
 

The characteristics of the two are different under the hammer. Both are butter soft, but the 1st piece seems to split easier. I have to pay close attention to the heat. The 2nd, the round bar, is more forgiving. It will split or crack on you, but only when I get really careless and try to work it colder than I should. 
 

I have a 3rd piece. It was a crowbar. I bought it at a tractor show in with a bunch of chisels, punches, sucker rod, and other scrap I assumed would be harden-able. When I got home and sparked it, I was surprised a crowbar wouldn’t spark much at all. I suspected it might have been WI and not steel.  Breaking it was inconclusive. There was a bit of separation, but not much. I tried soaking it in muratic acid for 24 hours and it was still smooth. At 36 hours I could make out some gray lines that looked like possible evidence, but wasn’t sure. After two hours in the muratic acid/H2O2 it was pretty clear. I wanted to take a picture, but had misplaced it. 
 

I am planning to place a piece of mild steel and another small piece of the crowbar in the acid tomorrow. The mild steel will serve as a control.