Chris Schwarz's Blog

Remove Rust, Zinc and Black Oxide with ‘The Works’

Three of the enemies in my shop are rust, zinc coating and black oxide.

1. Rust: No explanation needed. Rust is the enemy of steel, and steel is what allows us to tame wood.

2. Zinc coating: Many steel fasteners are coated with an ugly layer of zinc to protect them from rust in the outdoors. When I’m building stuff for inside, I’d rather not see the bright zinc.

3. Black oxide: Many pieces of reproduction hardware are coated with black oxide to protect them from rust during transport to market. This dull black oxide is difficult to strip off and looks wrong on reproduction pieces (in my opinion).

To tame these coatings, I usually use a citric acid solution or Evaporust to remove rust. Both are fairly safe chemicals that you can dump down the drain when they are spent. Citric acid also will remove zinc plating, though it struggles with thick coatings.

But neither of these chemicals can touch black oxide in my experience.

To remove black oxide, I usually use elbow grease – Simple Green and a woven gray pad. That’s a decent strategy for a big strap hinge, but it becomes ridiculous when you want to strip black oxide from 100 screws, such as those from Acorn Mfg.

(A personal plea to Acorn: I so wish you would sell your ferrous products without a black oxide coating. Many European hardware makers sell bare iron or steel hardware and do very well.)

So I have been looking for a way to remove black oxide that didn’t make me nuts.

Enter Charles Murray, an Ohio woodworker I’ve known for many years.

On Saturday, I ran into Charles while visiting the Woodworkers of Central Ohio. During our chat he mentioned he had been using “The Works” toilet bowl cleaner to strip rust from tools and hardware. And, he said, it’s about $1.50 for a 32 oz. bottle.

Intrigued, I picked some up at Home Depot and gave it a try today. I was shocked how quickly it removed some crusty rust from some T-hinges that have been sitting around the shop. Then I dunked some zinc-plated steel plates in the stuff. In 30 minutes it had stripped them bare – it took citric acid about six hours to do the same task.

Then I tried it on black oxide. I dumped some Acorn hinges into the solution and within 30 minutes I could wipe away the oxide and see bare metal.

What’s the catch? The Works is 20 percent hydrogen chloride. It is nasty stuff. You don’t want to touch it, breathe its fumes or get it inside you in any way. But when you are done with it you can put it in your toilet and it cleans it of lime scale, rust and hard water stains.

I do not like nasty chemicals. When I use them, I use them in small amounts, with great care and only when I think it is the best solution.

If you decide you want to use “The Works,” download its MSDS here. Read up on hydrogen chloride here. And check up on the product at its web site here. Use it with great care and adequate protection (chemical-resistant gloves etc.).

And ask Acorn and other hardware makers to stop using the ugly black oxide in the first place.

— Christopher Schwarz

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26 thoughts on “Remove Rust, Zinc and Black Oxide with ‘The Works’

  1. sailorjoe

    I tried this tip on an old Atkins rip saw my father left me. Frankly, I didn’t expect to ever be able to use that saw again, and I was just saving it to make card scrapers. But The Works worked. I soaked some paper towels in the solution and layer them over the saw, both sides. Because of the odor, I worked with the garage door fully opened. I let it sit in my garage workshop overnight. The next day, all the rust just wiped off. I rinsed the saw under the hose for 15 minutes, and thought I was finished. Oops! A day later, my saw was covered with rust again! The day after that, a small pocket knife that was laying on the bench also became covered in surface rust. Then the next day my scroll saw developed a coating of surface rust, which wasn’t there the day before. Apparently the chlorine fumes were settling on nearby surfaces, and eventually reacting with the water in the air. Lesson learned: use the Works outside and about mile away from the rest of my tools. I wish I had read these other comments before I tried the tip.

  2. gumpbelly

    Good job Chris.

    Even after fully explaining to do this, that and the other you got the hornets nest all stirred up. CHEMICALS!!!!!!!! we must run in circles and throw hands in air, whatever will we all do?

    I imagine some would post warnings if you suggested the use of butter, and a toothbrush.

    But on the other hand, thanks for the tip, I have some already, and will try it, WAYYYY cheaper than Evaporust.

  3. Christopher Hawkins

    For rust removal, I prefer the electrolytic method which is well described at http://www.instructables.com/id/Electrolytic-Rust-Removal-aka-Magic/. The great thing about this method is that it only attacks rust. You don’t have to worry about leaving the object in the rust removing solution too long and having it dissolve parts you want to keep. And besides, it looks way cool.

    One caveat, don’t use stainless steel as the electrode. You’ll make hexavalent chromium which is a very bad actor.

  4. woodnutbob

    Well I finally tried this on and old Plane Iron full of corrosion etc and probably 100 years of whatever. After 1/2 hour it was like brand new I am really impressed with the 1.78 investment at Home Depot.

  5. Tom Dugan

    A couple of data points to the discussion so far:

    Household vinegar does a fine job of removing zinc. Just remember to leave the lid unsealed as hydrogen gas gets released in the process.

    When mixing baking soda with water, aim for a saturated solution. Simply keep adding to water and stirring until no more dissolves. You’ll get a slightly higher concentration if you use warmer water, but I doubt that makes a measurable difference.

    Finally, if you go with TB cleaner you can always use your toilet to hold the pieces you’re stripping. Two birds, one stone! Err, chemical. Added benefit is that the little room should already have good ventilation.

  6. Jon

    Hydrochloric acid is used to pickle scale (oxide) from steel after it has been hot rolled. Its been many years since I worked at the steel mill, but I recall the concentration only being about 2 to maybe 5%. I don’t remember about the molarity of what they bought in bulk.
    So you might be able to dilute it a little more, but you always want to add it to water, not the other way around. HCL works by etching away the scale/metal interface, so it won’t take off any good metal unless you let it soak a long time. Having more surface area for it to work helps the pickling a lot. That was achieved by temper rolling, stretcher leveling the steel strip, or maybe shot blasting the metal.
    Rinse in hot water and dry off with a heat gun to help dry, maybe use a brush when rinsing if you want to really get rid of any chlorides, to avoid later rust spots. Most of the coils were coated with a light oil, to help keep the coils from rusting. Everything else in the building was rusty. Not really good to breathe in the fumes – it smells bad anyways.
    You could put some lime in the spent solution before disposing of it to neutralize it and dumping it out.

  7. shannonlove

    I suppose it’s owing to my original training as a biologist, with all the chemistry that required, but I am always amused to see people like woodworkers fretting over “harsh chemicals”.

    For people who spend their days working with very sharp and often very powerful cutting machines and all the other non-chemical hazards of the workshop, timidity towards chemicals seems as odd as a seeing a Marine intimidated by a drunken frat boy.

    I’ve been reading some of the pre-WWII, “boy mechanic” books and all those books assumed that 14 year old boys had access to arsenic to make pesticides or could whip up a barrette bearing by smelting tin and lead together and pouring it into a shaft. Oh, and the cover project is how to build a biplane style hang glider. You’d get lynched if you wrote a book like that today.

    Technologies are dangerous in direct proportion to their power and useful e.g. fire, and deserve respect but I think we’re being turned into chemophobic wimps.

    1. iwigle

      With respect, Shannonlove, HCl sold as Muriatic acid for brick and concrete cleaning approaches 10 Moles/litre concentration. (35% by weight is 35 grams per 100 or 350 grams per 1000, roughly 10 moles/litre) This is from my post-graduate training as an organic chemist. This will cause immediate heavy chemical burns to exposed skin, and probably blindness if eyes are exposed to a spill.
      The solutions you may have used working with biological smaples were, I suspect, much more dilute, so that they did not harm the specimens you were examining.

      I share your view that many of the cautions we are confronted with today are extreme. All the way down to McDonald’s warning on the cup that their coffee is hot. But some cautions ARE appropriate.

      A word about the realities of muriatic acid (Hydrogen chloride or HCL). In its native state, HCL is a gass at room temperature. When it evaporates from the top of a container of Muriatic acid solution such as apbeelen describes, you have pure HCL in the air. Ions do not exist in air. They are either combined with another ion to create a solid like Salt, or they are in a liquid solution. I’m afraid that you are incorrect in your chemical analysis. Pure HCl was combining with the metal on the surface of the items in apbeenen’s basement.

      Though your comments were doubtless well intended, they are frankly dangerous when presented in this setting, where most folks depend on the accuracy of what they read.

      So everyone, rather than take my word for it, go and double check with the nearest person you know who was trained as a chemist – the parmacist in your local drug store. And if I am wrong – I’ll eat that. But I do not think that is what you will find.

      You wouldn’t use your table saw without a guard and eye protection. Please exercise comparable caution here.

  8. apbeelen

    I’ve used plain vinegar to remove rust. I don’t know if it works for zinc and black oxide, but I think I’ll try it. If you leave metal parts in vinegar too long, it will eat the metal though, so you have to be careful. You’d hate to put a tool or antique piece of hardware in vinegar to remove the surface rust and end up with a pitted piece of scrap metal (I’ve done it). The metal will also be a dull gray, not a nice steel color, but this may be brightened up with a little steel wool and elbow grease.

    A note on muriatic acid – it’s harsh! I left a bucket of it uncovered in my basement for a few months by mistake, and almost every bare steel object in my basement has a layer of surface rust on it…nails, tools, pipes, etc.

    1. shannonlove

      Muriatic acid is HCL or hydrogen chloride. When it evaporates into the air, the chlorine ends up as ionic chlorine just as in common salt. When it deposits on metals, it creates the same effects as salt.

      That’s also why you have to throughly rinse any metals treated with muriatic acid/HCL after using it for any treatments.

    2. woodstudio

      I’ve also used a mixture of white vinegar and water to remove rust. Submerge the item if possible. The timing is determined on the how bad the rust is and how diluted the vinegar is. Just keep checking until it is done. I’ve left items in overnight with no issues.

  9. Jwoodrow

    Thanks for the info. Good to know. I am curious – after you have removed the zinc or black oxide from hardware, do you coat it with anything or just leave it alone? Thank You.

  10. GTBurbank

    I’m gonna remind y’all of this discussion the first time someone gives megan crap for shop uses of common household cleaning chemicals. That said, use this stuff with caution. Open windows, fan for cross ventilation, respirator. And that’s just when you are cleaning the toilet!

  11. Bob Miller

    I have heard that chlorine exposure to steel makes it much more likely to rust with horror stories about tool chests left near washing areas (bleach). Have you experienced anything similar?

    Or have the warnings for aluminium and stainless steel accidentally been transferred to plain steel?

  12. iwigle

    Hydrogen Chloride is also known as hydrochloric acid, and also as muriatic acid. Readily available as muriatic acid wherever pool chemicals are sold for cleaning concrete. And as it gets more concentrated it works faster, and is also more hazardous… Chemical-resistant gloves, eye protection, and lots of fresh air.

    Also, the sodium bicarb can also fizzing just because it gets used up. I’m sure soundwoodwork would agree the test is that after it stops fizzing, add a bit more bicarb, and you are done if fresh bicarb doesn’t fizz.

    Chris-thanks for the suggestion.

    Cheers,

    Ian

    1. Jim McCoy

      Fe3O4 + Fe + 8 HCl –> 4 FeCl2 + 4 H2O (for the black oxide). The equations point out that you lose additional iron when you chemically remove the oxide with an acid.

  13. fletcherj

    A safe way to deal with left over HCl is just keep adding baking soda until it stops bubbling and fizzing when you add more. The baking soda will neutralize your acid and make disposal a case of dealing with salty water.

    Other alternatives include clay based cat litter.

    Do you not use phosphoric acid as it leaves that dull coating of iron phosphate?

    1. soundwoodwork

      One note on the baking soda trick: make sure you mix the solution well; I’ve had plenty of times where I’ve been trying to neutralize an acid with sodium bicarbonate (active ingredient in baking soda) where it would stop fizzing before it had fully neutralized the acid. Just a matter of making sure that the bicarbonate mixes with the entire solution. (this comes from being an organic chemist, I have to neutralize acids in this manner a fair amount)

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