With one natural ingredient, it’s easy to remove years of rust from antiques, artifacts, and tools.
A few months after I sold my first horse, I was walking through the pasture and found a shoe he’d lost sometime in the year before. Looking at it, I thought it would be a nice keepsake- and something I could use to create an equestrian project with sentimental value- it was covered with layers of rust.
I’d been experimenting all winter with using citric acid to clean rust off garden tools that I, in my easy distractability, tend to leave out in the elements. As it turns out, the basic combination of citric acid, water, and time completely removes rust from metal. I was pretty thrilled, especially after trying and mostly failing to remove rust from tools with caustic chemicals like CLR and The Works. A common ingredient in canning recipes, citric acid is an organic acid a little stronger than vinegar, depending on the concentration you mix it in.
2019 Update: I’ve loved reading your feedback on this article and how many of you have found this tutorial useful! FYI A lot of the comments have suggested replacing citric acid with vinegar and soaking a little longer, but to have success with vinegar takes several weeks and more money’s worth of vinegar, so for a faster, cheaper result, stick with the Citric Acid.
Supplies You’ll Need:
- A bucket or plastic container large enough to hold your rusted object(s)
- Very hot water
- A surface treatment for raw metal. Oil or clear coat varnish works.
- Pure Citric Acid – You can buy this wherever canning supplies are sold, however, the pricing on citric acid sold for canning includes a huge markup. As of spring 2020, Ball brand citric acid is priced over $1/ounce but a 5 lb bag of food-grade Citric Acid is 21¢/ounce.
My advice is to order in bulk and don’t worry about having too much – it’s SO handy for cleaning! A tablespoon of Citric Acid is great for boosting dishwasher detergent, descaling coffee makers, getting grime off pots and pans, removing hard water stains, and general cleaning. You can use it in cooking too- soaking cut apples in a weak citric acid solution to prevent browning, or adding a tablespoon to bone broth at the beginning of the cooking process to help break down bone and transfer nutrients into your broth.
1. Scoop the powdered citric acid carefully into your bucket. I add about 1/3rd cup of powder per gallon of water, but you can use more or less depending on how rusty your object is and how quickly you need results.
2. Fill your bucket with very hot water and stir to dissolve the citric acid powder completely into the water. There should be no grit at the bottom of the bucket.
3. Place your rusty object in the solution. In this case, I’m de-rusting the horse shoe and I’ve tossed in some rusty bolt cutters since I’ve got project all set up.
The remaining rust in the grooves of the horse shoe bothered me, so I remade my solution and let it sit overnight.
DO NOT reuse the same solution for a second round. The chemical reaction that dissolves the rust changes the chemical makeup of the solution, making it ineffective for additional rust removal.
When you are pleased with your object’s new finish, dry it completely. The metal may seem “dirty” and rub off dark marks on your hands, this is normal for steel and iron with no protective coating. Make sure the object is totally dry (10 minutes in a 300-degree oven works great as long as the item is 100% metal with no plastic grips or other heat-sensitive portion) and then add a finish protectant.
You MUST protect the finish. If left uncoated, the unprotected metal will rust again almost instantly. You can apply clear coat / lacquer, or just spray with cooking oil and wipe away the excess oil.
2020 Update: Vinegar vs Citric Acid
Since published, this article has traveled far and wide and collected a lot of feedback comments- many indicating that “just use vinegar” was a comparable technique. Recently, I decided to do a side by side comparison of vinegar vs citric acid in my kitchen. Without repeating the entire rust removing process (difficult to compare with scrutiny, since no two objects rust exactly alike) I ordered some pH testing strips.
To be the “better” rust-removing solution, the winner would need to be 1. higher in acidity, 2. lower in cost, or 3. both. My suspicion was that citric acid would win by a landslide, but my experiment progressed.
I mixed one cup of citric acid solution at the concentration recommended above (.33 cup per gallon, or in this case, 1 tsp citric acid to 1 cup water) and tested it against a leading name brand of undiluted white vinegar.
RESULT #1: ACIDITY
At the recommended dilution, Citric Acid solution is slightly more acidic than vinegar– matching the scale in my pH testing kit at a pH of 3, compared to the name brand distilled white vinegar at pH 4. (Interestingly, according to the internet, the pH of distilled white vinegar should be between 2-3, meaning either my name-brand vinegar was weak or, more likely, my pH testing kit was not lab-accurate. Even if this is the case, I anticipate the values relative to other values read by the same test strips should generate accurate comparisons)
But how do they measure up in terms of cost…
What happens if I heat vinegar and add salt?
Comments on this post have casually suggested “heating vinegar and then adding salt” to create a rust-busting cleaning solution. However, combining salt and vinegar creates Hydrochloric Acid. Combining heated vinegar with salt creates hydrochloric acid fumes, which are toxic and potentially fatal in large doses. Unlike citric acid neutralized through rust-dissolving, hydrochloric acid is also difficult to dispose of safely. A simple-language Wikipedia article explains this.
RESULT #2: Cost of Vinegar vs Citric Acid
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