Emilie Meyer
Stainless steel is a popular material for kitchen utensils and cookware due to its durability and aesthetic appeal. However, it is not uncommon for stainless steel items to develop black spots or residue, which can be frustrating for those who value the appearance of their kitchenware. These black spots may be caused by several factors, including improper cleaning techniques, residue from manufacturing processes, or corrosion due to exposure to certain chemicals or high heat. While these spots are usually cosmetic and do not affect the functionality of the items, they can be challenging to remove and may indicate potential issues with cleaning methods or water quality. In this article, we will explore the possible causes of black spots on stainless steel and provide tips for prevention and removal.
What You'll Learn
Black spots may be caused by corrosion pits
Black spots on stainless steel pans can be caused by corrosion pits. This is technically not a stain but an erosion of the surface of the metal. Pitting on stainless steel occurs in the presence of chlorides, like salt. Even a small amount of salt left in a pan can cause pitting once all the water is gone.
The reason why stainless steel is resistant to corrosion is because it contains chromium. Chromium reacts with oxygen in the air to form a thin layer of chromium oxide on the surface. It is this layer of chromium oxide that makes stainless steel passive and protects the steel from reacting with oxygen and rusting. However, when undissolved salt is added to a stainless steel pot, the chloride in the salt can attack the passive layer of chromium oxide, leaving pockmarks where it removes the oxide.
Pitting corrosion refers to small areas of corrosion that can appear as punctiform holes on the surface of stainless steel. In the depths of the material, the corrosion often expands significantly and remains unnoticed for a long time because of the low visibility on the surface.
To prevent pitting from occurring, it is important to wash stainless steel items immediately after use and to dry them thoroughly. It is also important to avoid using abrasive metal cleaners or harsh soaps, as these can scratch the surface and leave irreparable damage.
If your stainless steel pan already has pitting, there are a few ways to try and remove the stains. First, try washing the pan with a mild detergent. If that doesn't work, you can try using a commercial cleaner specifically designed for stainless steel, such as Bar Keepers Friend. You can also try making a paste of baking soda and water and using a soft cloth to rub the mixture onto the affected areas.
If the pitting is severe, it may be necessary to grind out the pitted areas and then passivate the surface. This involves treating the surface with an acid such as citric acid or lemon juice to prevent further corrosion.
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Osmium and/or ruthenium deposits could be the reason
Osmium and ruthenium are silvery-white or silvery-blue lustrous metals that are generally found in the metallic state. They are stable and highly resistant to corrosion. However, in certain conditions, they can form black deposits on stainless steel.
Osmium and ruthenium are extremely rare, but they are sometimes found as impurities in precious metals like gold and platinum. When these precious metals are melted, the presence of osmium and/or ruthenium impurities can result in the formation of black dot deposits on the bottom of the container. This is due to the oxidation of osmium and/or ruthenium compounds, which can occur when they come into contact with basic solutions such as soap and water.
In the case of your stainless steel pan, it is possible that there are trace amounts of osmium and/or ruthenium present as impurities, which have reacted with the soap and water used for cleaning, leading to the formation of black spots. These spots may be challenging to remove, even with vigorous scrubbing or the use of baking soda.
Additionally, during nuclear fuel reprocessing, ruthenium can form black ruthenium deposits on the stainless steel walls of process equipment. This is due to the reaction of ruthenium with other compounds in an alkaline medium, which results in the oxidation of ruthenium compounds and the formation of black deposits. While this scenario may not be directly applicable to your pan, it demonstrates the potential for ruthenium to contribute to black spots under certain conditions.
To address this issue, you could try the following methods to remove the black spots:
- Wash your pan with a mild detergent and observe if the spots disappear.
- Apply a small amount of olive oil to the pan, let it sit, and then wipe it out.
- Scrub the pan with a mixture of lemon juice and salt or baking soda and warm water.
- Ensure that you wash your pan immediately after use and dry it thoroughly to prevent food or water from lingering on the surface.
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Abrasive cleaning methods may be to blame
To prevent this, wash all of your items immediately after use, especially flatware. By letting food linger on utensils, you are allowing the food to work away at the protective layer of the steel. Also, be sure to dry the items immediately and not let them sit for long periods in water or with water on them.
Additionally, avoid putting your stainless steel flatware in the dishwasher because the flatware will rub against one another, breaking apart the protective barrier that helps keep the black spots and rust away. Never wash a stainless steel item with an abrasive metal cleaner or harsh soap, as these could scratch the surface and leave irreparable damage.
To remove the black spots, try washing them away with a mild detergent. However, it is highly possible that you will not be able to fully remove the black spots. If the black is removed, then it may be something other than rust.
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Black residue may be left over from the manufacturing process
Black spots on stainless steel can be frustrating, especially if you've just bought a new set of cookware. These spots could be appearing because you are using an abrasive cleaning method that removes the protective chemical layer on your stainless steel items. If the protective layer is gone, the stainless steel is at risk when it comes into contact with cleaning supplies or food.
- Spread a small amount of olive oil on the inside of the pan, let it sit, then wipe it out. After that, wash the pan with dish soap and hot water.
- Gently scrub the pan with a mixture of lemon juice and salt, then wash.
- Some stainless steel cookware comes with instructions to scrub it gently with a 1:1 mix of baking soda and warm water before use.
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The black spots could be burnt-on oil
If your stainless steel pan has black spots, it could be burnt-on oil. This is a common problem, especially if you've recently moved into a new home and are still getting used to a new cooker. It's easy to do – perhaps you heated up the pan for too long before adding the oil, or you heated oil without adding food soon after. Either way, you're now left with a pan with large brown or black marks on the cooking surface.
The good news is that there are several ways to remove burnt-on oil from your stainless steel pan. Here are some methods you can try:
Bar Keepers Friend
This product is recommended by several sources for removing burnt-on oil and food from stainless steel pans. It's a mild oxalic acid that can dissolve away deposits.
Baking Soda
Make a paste with baking soda and water, and leave it in the pan for at least 30 minutes. Then scrub it gently with a plastic scrubber. For really bad burns, leave the paste in for longer.
Vinegar
Boil some white vinegar for about a minute (don't let it boil dry) and then scrub the pan. Or, for a gentler approach, add some vinegar to the pan with some water and simmer. Vinegar contains acetic acid, which breaks down burnt-on food.
Dish Soap and Water
Sometimes, this is all you need. Add dish soap and water to the pan, bring it to a simmer for a few minutes, and then scrub. If the burnt-on food is still stuck, try soaking the pan overnight.
Lime Juice and Salt
Let the mixture sit in the pan for several minutes, then sprinkle in some more salt and scrub.
Cream of Tartar
Slather your pan with a mixture of water and cream of tartar, which contains potassium hydroxide and tartaric acid. Let it soak overnight and wipe clean in the morning.
Cola
Pour some cola into your pan and simmer gently. Then scrape off the burnt-on oil. Cola is super acidic and works well to loosen burnt-on messes.
Tomato Sauce
Pour in a generous portion of tomato sauce or crushed tomatoes and simmer gently for several minutes. Tomato sauce will remove burnt-on food due to its acidic nature.
Steel Wool
Some sources recommend using steel wool to scrub burnt-on oil from a stainless steel pan. However, this may scratch the pan, so use with caution.
Other Tips
- Avoid using harsh, abrasive metal cleaners or harsh soap, which can scratch the surface of your pan.
- Wash new stainless steel pans gently before the first use.
- Dry your pans immediately after washing them, and don't leave them to soak in water.
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Frequently asked questions
Black spots on stainless steel are usually caused by corrosion or residue from the manufacturing process. Corrosion can occur when stainless steel comes into contact with salt or abrasive cleaning products, removing its protective chemical layer. New stainless steel items may also have a black residue from the polishing process, which can be removed with oil, lemon juice and salt, or baking soda and warm water.
To remove black spots from your pan, you can try using a mild detergent, or an acid-based cleaner like vinegar or Bar Keepers Friend. For new items, you can try adding a small amount of olive oil to the pan, letting it sit, and then wiping it out before washing with dish soap and hot water.
To prevent black spots, wash your items immediately after use, dry them straight away, and avoid using abrasive metal cleaners or harsh soap, which can scratch the surface.
