Oxidation is often our enemy. When oxygen contacts metals, it reacts with the surface atoms to form what is known scientifically as an oxide, but more commonly as rust, or tarnish. While in the case of some metals—such as copper—oxidation can result in a beautiful green colour, in the case of silver or iron it case cause damage.
Especially in the case of iron or steel, rust causes pitting and weakening and can be very difficult to remove. We often run in to similar problems in the internal mechanisms of mechanical pencils, which are often made of brass. A build-up of oxidation can cause parts to seize together or become gummy.
So, oxidation can be our enemy. Happily, the solution is simple, safe, and cheap: lime juice.
Citric acid has long been known as a very effective chellation agent. In simple terms, this means that it literally removes the top layer of metal atoms; since the top layer of atoms is bound up with oxygen, as tarnish, this is a good thing.
How to Use Lime Juice to Remove Rust and Tarnish
- Pour together in a glass bowl: 1 part lime juice, 3 parts vinegar;
- Microwave until warm (this speeds up the reaction time);
- Submerge the tarnished item in the solution, and leave for about an hour (or as long as overnight);
- Wash off the item with warm, soapy water, using a soft brush. A dark, almost sludgy layer will come off, leaving a dull layer of metal. Polish if desired.
Using this method even stubborn and pitted steel and iron will come out clean, including the fiddly detail in Victorian cast iron. And while this method does remove metal, the amount is very negligible, most of which was beyond recovery, bound up with oxide atoms. (One word of caution: some gold plating can be very thin, especially if produced in the last 50 years or so. You might want to use another method on items like this.)
An additional benefit is that this solution, although acidic (with a pH of about 3) is safe for plastics and wood, and won’t compromise many adhesives (cyanoacrylates, like “crazy glue” being a notable exception).
As an aside, it’s quite amazing how much oxidation just a bit of this solution can remove. Even if it looks grey and sludgy, there is still quite a bit of reaction-power left in it.
A Note on ‘Patina’
Does this method affect the patina of a metal item? Yes, and no, depending on your definition of the word. Courtesy of the Oxford English Dictionary:
- a. A thin coating or layer; spec. an incrustation on the surface of metal or stone, usually as a result of an extended period of weathering or burial; a green or bluish-green film produced naturally or artificially by oxidation on the surface of bronze and copper, consisting mainly of basic copper sulphate (cf. verdigris n.).
In this case, a resounding yes! Destructive oxidation will be gone. So will the brown colour that develops over a few weeks or months on copper, brass, or bronze.
One notable warning: in some cases (particularly in “Arts & Crafts” metal pieces) a specific chemical finishing process was used in their manufacture, resulting in a highly-sought colouration. This method will remove that finish. This is the “patina” most misunderstood by antique dealers, many of whom use it’s legend as an excuse not to spend time cleaning anything. A factory patina should not be confused with destructive oxidation, like rust. And, to our knowledge, few items made of silver were ever intended by their makers to remain blackened by tarnish.
- b. A gloss or sheen; spec. that on wooden furniture produced by age and polishing.
- c. fig. An acquired accretion of an abstract quality; a superficial impression or appearance.
In these cases: the small signs of use that, over time, make something beautifully imperfect; the ancient ‘feel’ of an antique? No. You are cleaning it, thoroughly. But small dents and surface scratches will remain.
Soaking metal in acid as a means of cleaning it is a serious step, and should only be done according to the rules of restoration and conservation: when needed to halt or repair damage. But when you need to do it, lime juice is fast, cheap, easy, and safe. The very definition of the most effective tools we have.