People might think that a material known as “stainless” is completely free from all kinds of stains, but this is not the case with so-called stainless steel. While this material is certainly less susceptible to rust discoloration than ordinary steel, stainless steel will definitely stain.
Stainless steel is most accurately considered stain-resistant, not totally impervious to stains.
What allows stainless steel to maintain its luster longer than other types of steel is a protective layer of chromium oxide on its surface. Chromium oxide is a type of rust. Unlike iron oxide, which most people are familiar with, the chromium oxide layer generally does not flake off. It exposes more of the underlying metal to corrosion. The protective layer makes it easy to remove most stainless steel stains, preventing people from using the wrong cleaning agent or implement.
What is stainless steel?
Ordinary steel is a metal alloy. Its main component is iron, and it also contains up to 2 percent carbon and small amounts of other elements, such as silicon, phosphorus, sulfur, and oxygen. Manufacturers add chromium to the alloy when making stainless steel; chromium is generally 10 to 30 percent. For durability and workability, they usually also add other elements such as nickel and manganese. The combination makes typically stainless steel non-magnetic.
Chromium is a metal that combines with oxygen to form chromium oxide, which is super hard. This compound includes a thin, continuous layer on the stainless steel surface that prevents further corrosion and prevents ferric oxide (iron oxide) formation. This layer can heal by itself and will re-form when you scratch the surface of the metal.
Types of stains and corrosion
Cleaning Hard water can cause a stainless steel sink to become cloudy.
The sleek, shiny finish of a stainless steel sink can become cloudy or discolored for many reasons. You can get rid of most of these stains, but some are permanent.
- Hard water: Minerals in hard water can build up in any sink. Calcium deposits will make it cloudy. The main reason for unsightly brownish rust stains appears in many old bathrooms, and kitchen fixtures are dissolved iron.
- Chlorine and chlorides: Chlorine may cause a type of corrosion known as pitting. Sodium chloride is a kind of chloride, so it will also cause corrosion. Short periods of exposure are no problem, but prolonged exposure, such as allowing saltwater or water containing chlorine to be placed in a stainless steel sink, can cause this type of pitting, which is irreversible.
- Bimetallic corrosion: Saltwater stay in the sink may create another stain and corrosion. Saltwater is an electrolyte, meaning it conducts electricity. If any kitchen utensils are made with a different metal, such as aluminum, if i’s sitting in the sink, the exchange of electrons between the metals could corrode it.
- Acid staining: Any liquid with a pH below 1.0 can stain stainless steel. A liquid with such a low pH is an acid that is too strong for everyday use, but certain sulfuric acid-based drain cleaners may qualify. Avoid putting them in the sink.
- Iron stain: Cleaning the stainless steel sink with steel wool will scratch the sink surface, and the delicate pieces of iron left on the stainless steel surface can reduce the concentration of chromium, and when it drops below 10 percent, the sink will rust. You can remove this rust and the iron that caused it, and when you do, the chrome rust layer will repair itself and prevent more rust from forming.
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A general stain removal procedure
You should always check the manufacturer’s instructions for cleaning the stainless steel sink. The following simple cleaning method for most stains is most recommended:
- Mix baking soda with dish soap to make a paste.
- Soak a sponge or microfiber cloth in the paste to saturate it. You can also use an old toothbrush.
- Wipe stains gently and repeatedly, always following the grain lines of the metal until the stains disappear.
Wash the sink weekly with a sponge or cloth and dishwashing soap or other cleaning products for general care. Mild abrasive cleaning powders, such as Comet or Bon Ami, are recommended. One sink dealer suggests placing the stopper in the sink, pouring in a bit of mineral water, and using it to clean the metal for a bright, shiny finish.
Check the ingredients of any product you use. If the product contains chlorides, do a thorough rinsing of the sink after cleaning to avoid pitting.
Get rid of calcium and rust stains.
Scrubbing with baking soda is the most recommended method for cleaning stains.
Calcium and iron stains from hard water are challenging to remove from any sink. However, using the vinegar will help to dissolve the stains but is not acidic enough to damage the sink. A good way to use it is to spray vinegar in the sink after cleaning with baking soda and dish soap paste, but before rinsing. It will make the baking soda bubble, which is fun to watch, and when you wipe off the paste and rinse after about 20 minutes, the stains should be gone.
It’s a little more difficult to remove rust stains from scratching with steel wool or some other abrasive metal cleaning implement. The easiest solution is to clean with a cleaner containing oxalic acid, such as Barkeeper’s Friend. If you prefer a do-it-yourself method, make a paste with vinegar and laundry detergent, cover the stain and let the paste sit for an hour or two. Spray with more vinegar if it has a stain of dry pasta. The rust should disappear when you wipe off the paste, but you will still need to rinse and clean the sink thoroughly to remove all the small metal fragments that caused the rust.
In addition to avoiding steel wool and chlorine or chloride products, you should never use oven cleaners to clean your sink. It contains caustic soda, an ingredient in many industrial-strength drain cleaners, which is as bad for the finish as a strong acid.
Avoid soaking cast iron cookware in a stainless steel sink. Small pieces of iron can migrate through the water and cause iron stains in the sink.