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Rust spots on cutlery - causes and solutions when washing in the dishwasher

Mateusz_konstruktor 27624 41
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Why do small rust spots appear on cutlery washed in a dishwasher, and what can I do to stop them?

The spots are usually the cutlery corroding in the dishwasher, often because of older or lower-quality stainless steel combined with aggressive detergent, high temperature, or wrong salt/water-hardness settings [#20121959] [#20128617] Use a lower-temperature eco or shorter program, and make sure the dishwasher’s hardness setting and salt use match the water hardness; for soft or medium water, the manufacturer may advise not adding extra salt together with all-in-one tablets [#20120652] [#20120974] [#20128617] Also check the cutlery basket and racks for cracked plastic coating or other damage that could expose metal and accelerate corrosion [#20121316] Cleaning filters and the drain is good maintenance, but the standing water in the sump is normal and is not presented as the main cause of rust on the cutlery [#20120011] If the set is old and valuable, hand washing may be the safest option [#20121959]
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  • #31 20127539
    mipix
    Level 38  
    Posts: 4049
    Help: 489
    Rate: 1457
    For interested. After using this invention, the stains on the cutlery are the same as before, I don`t see any difference. The instructions say this is to catch loose bits of rust. After thinking about it, I don`t know where the loose pieces of rust in the dishwasher would come from. It is a neodymium magnet pressed into a block of aluminum. VooDoo product from the Energy Saver series.
    Rust spots on cutlery - causes and solutions when washing in the dishwasher Rust spots on cutlery - causes and solutions when washing in the dishwasher

    Sample reviews from Amazon:
    Spoiler:

    Actually not even worth one star. I`ve had the rust repellent for about 6 months and it has worked great. Unfortunately this product is a complete disappointment and is black after 5 uses! And I have more rust spots than before.
    *
    Cutlery in the dishwasher comes out of the rinse with rust stains despite the rust repellent. The rust repellent is in the cutlery basket and has a compartment to itself - the cutlery is spread out in the other compartments. To be honest: with Rostschreck there are even more stains on the cutlery. This would be a great idea - unfortunately it doesn`t work.
    *
    I`m not one to give negative reviews, I usually stay silent, but this product deserves a review. Theoretically, all this could work is that the rust particle is attracted to the rust repellent. In practice, however, it turns out that after the third rinsing process, the rust remover has significant dull spots. After another 5 rinses, the dull spots became rust spots. Cutlery that needs to be protected from rust will rust and stain, making it unappetizing (not cheap cutlery, but a 320 euro cutlery box). This product is the worst I have ever purchased from amazon. As an amazon, I would consider removing the product from your portfolio as it would only damage your reputation.
    Conclusion: product worse than bad, sent back after 8 weeks, bought a new cutlery box ........ expensive experience


    I wonder if electrolytic coating of cutlery with nickel/chrome (I don`t know, I`m not a chemist) might solve the problem. Spots always appear in the same places, in micro pits. A layer of non-corrosive metal probably makes sense.
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  • #32 20127770
    viayner
    Level 43  
    Posts: 10546
    Help: 1557
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    Hello,
    the observed phenomenon is electrochemical corrosion, it occurs when two different metals come into contact in a conductive environment, and most often appears in places of micro-defects.
    Magnet for burning off loose pieces of rust - :) Oh, I haven`t laughed so much in a long time, soon there will be a magnet to catch ions.
    You can test that the cutlery is not touching anything, and avoid combinations of multiple metals at the same time, e.g. aluminum pots and steel cutlery.
    Regards
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  • #33 20127907
    misiek1111
    Level 37  
    Posts: 3969
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    Rate: 1047
    viayner wrote:
    the observed phenomenon is electrochemical corrosion, it occurs when two different metals come into contact in a conductive environment, and most often appears in places of micro-defects.

    That is ?
    William Bonawentura wrote:
    Remove the baskets and carefully check whether there is any crack in the plastic coating surrounding the wires.
  • #34 20127967
    viayner
    Level 43  
    Posts: 10546
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    Rate: 2003
    Hello,
    In simple terms, when two different metals are in contact and are in the electrolyte, we have this phenomenon.
    Here, for example, a fork and a knife made of different alloys create electrodes, and the electrolyte is water with salt or a washing tablet.
    Chemical corrosion may also occur here thanks to a rather aggressive washing tablet. Have you noticed the amount of deposits that appear in the presence of aluminum-type dishes compared to their absence?
    I agree, a basket with damaged coating will be "helpful" here
    Regards
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  • #35 20128189
    Janusz_kk
    Level 39  
    Posts: 5679
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    viayner wrote:
    Have you noticed the amount of deposits that appear in the presence of aluminum-type metal utensils compared to their absence?

    We didn`t notice because we haven`t used such dishes for a long time :) and I doubt anyone else uses it.

    viayner wrote:
    In simple terms, when two different metals remain in contact and are in the electrolyte, we have such a phenomenon.
    Here, for example, a fork and a knife made of different alloys create electrodes, and the electrolyte is water with salt or a washing tablet.

    I highly doubt that anyone else has aluminum spoons, generally cutlery is made of steel, so it`s not electrolysis or anything related to it.
  • #36 20128507
    viayner
    Level 43  
    Posts: 10546
    Help: 1557
    Rate: 2003
    Hello,
    Janusz_kk wrote:
    ...generally, the cutlery is made of steel, so it`s not electrolysis or anything related to it.

    of course it`s not electrolysis, no one mentioned it, it`s electrochemical corrosion, it`s enough that these are two slightly different metals/alloys and the cell is ready.
    As for aluminum pots, I advise you to look carefully at what your colleagues have, often "pots", especially lighter and cheaper ones, are made of alloys containing Al-Mg and derivatives, damaged enamel/Teflon is enough, so I guess many of you have it, the same with handles, screws etc.
    Regards
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  • #37 20128589
    Janusz_kk
    Level 39  
    Posts: 5679
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    viayner wrote:
    of course it`s not electrolysis, no one mentioned it, it`s electrochemical corrosion, it`s enough that these are two slightly different metals/alloys and the cell is ready.

    It is the same, electrochemical corrosion occurs as a result of water electrolysis. But this is not the case in the dishwasher with steel cutlery, slight differences in composition do not affect the potential. Cutlery rusts from caustic soda and temperature.

    viayner wrote:
    As for aluminum pots, I recommend taking a closer look at what your colleagues have

    What do I care about my friends, I don`t care. Aluminum is harmful and that`s why I doubted that anyone had such pots, and if they did, they had to be washed by hand.
  • Helpful post
    #38 20128617
    Ktoś_tam
    Level 40  
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    Question:
    What was used in the dishwasher to wash? What were the pills, more basic or all-in-one, and were they dosed with salt? If salt was dosed, was it at factory settings? What about water hardness?
    I`m asking because the dishwasher manufacturer recommends not adding salt to the tablet with the water softening function (with salt?) for soft and medium water. Maybe that`s where the rust marks come from.
  • #39 20129128
    viayner
    Level 43  
    Posts: 10546
    Help: 1557
    Rate: 2003
    Hello,
    Janusz_kk wrote:
    ...What my friends care about, I don`t care. Aluminum is harmful and that`s why I doubted that anyone had such pots, and if they did, they had to be washed by hand.

    my friend is quite rude towards other colleagues.
    As for the theory of electrochemical corrosion, please stop creating new chemistry or keep your ideas to yourself.
    Regards
  • #40 20129135
    Janusz_kk
    Level 39  
    Posts: 5679
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    viayner wrote:
    my friend is quite rude towards other colleagues.

    Because I`m writing about my experiences with the dishwasher.

    viayner wrote:
    As for the theory of electrochemical corrosion

    I suggest starting with yourself.
  • #41 20132858
    Mateusz_konstruktor
    Level 37  
    Posts: 4156
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    Rate: 1099
    I repeat.
    pilomatt wrote:
    You add salt and then pour water right up to the cork.

    Quote:
    Right under the cap, without any free space in case of volume changes due to temperature changes?

    Here the situation was such that while unscrewing the plug, fluid flowed out from the tank, pushed out by a slight overpressure.

    Rust spots on cutlery - causes and solutions when washing in the dishwasher
    Maybe you need to leave some free space, as is done when filling various tanks?

    Janusz_kk wrote:
    Mateusz_konstruktor wrote:
    I didn`t have this problem for the first two years and I want to get it back.

    After all, I wrote to you, the problem is with poor steel and it has been there from the beginning, but it is not visible.

    These are knives made of really solid material, from the 1970s.
    At the same time, either it`s just a coincidence, or "plain supermarket" cutlery purchased a few years ago seems not to be susceptible to this problem. :roll:

    William Bonawentura wrote:
    Remove the baskets and carefully check whether there is any crack in the plastic coating surrounding the wires.

    Generally, I would not expect this considering the perfect general condition of the device, I will check it only when the interior currently occupied by dishes is unblocked.

    Chris_W wrote:
    Once I used a stainless spoon as an anode for electrolysis - (as you write - from a quite expensive old set) - there was half a millimeter of stainless steel on the surface, and ordinary steel inside - of course, the electrolysis ate away the center and left a shell of the spoon. ;)

    Upload a photo and we will compare.

    homo_sapiens wrote:
    This is a clever marketing gimmick...

    In the 1970s, production and distribution were generally based on marketing tricks.

    Janusz_kk wrote:
    The biggest problem is the cutlery that turns black, some spoons are almost black.

    Post a photo, there will be something to discuss.

    Ture11 wrote:
    ...this level should not be so high with this filter chamber design. Maybe after the program was turned off, the dishes dripped so much, but it never happened to me. Some water always remains there (about 2 cm from the bottom), because the pump is not able to pump out all of it (the pump has an inlet from the side of the bottom).
    I will quickly believe that you have a damaged check valve behind the pump and that the water from the drain pipe flowed back into the chamber (after the pump turned off, immediately or after some time). Except that this amount of dirty water has no effect on anything. And immediately after starting the program, the water should be poured out by the pump as much as it can.

    Rust spots on cutlery - causes and solutions when washing in the dishwasher
    Rust spots on cutlery - causes and solutions when washing in the dishwasher

    The end of the ruler is placed near the sensor, not at the very bottom.
    Rust spots on cutlery - causes and solutions when washing in the dishwasher
    I have previously pulled out pieces of a long-broken cup from the deepest recesses and for this reason I am wondering whether such an amount of water in this place is appropriate. Maybe the drain channel is partially clogged and the drain needs to be unscrewed and at least emptied of any pieces of the cup that may still be there?
  • #42 20132862
    gorki73
    Level 39  
    Posts: 3619
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    Mateusz_konstruktor wrote:
    Maybe the drain channel is partially clogged and the drain needs to be unscrewed and at least emptied of any pieces of the cup that may still be there?

    Well, you won`t know anything without disassembling it.
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Topic summary

✨ Rust spots on cutlery, particularly those made from stainless steel, can arise from several factors when washed in a dishwasher. Common causes include leaky salt containers, delayed removal of cutlery post-wash, and the use of aggressive washing tablets. Users noted that older cutlery, such as those from the brand Gerlach, may be more susceptible to corrosion due to inferior protective coatings. Solutions discussed include ensuring proper maintenance of the dishwasher, such as cleaning filters, adjusting water hardness settings, and using appropriate washing programs. Lowering the wash temperature and avoiding the combination of different metal types in the dishwasher can also help mitigate rust formation. Additionally, some users suggested that electrochemical corrosion could occur when different metals come into contact in a conductive environment, exacerbated by the presence of salt or aggressive detergents.
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FAQ

TL;DR: 13 % of dishwasher owners notice rust specks on cutlery each year [Finish, 2020]. "Lower water temperature will definitely help" [Elektroda, Janusz_kk, post #20120652] Key fixes: seal the salt cap, match water-hardness settings, remove items promptly.

Why it matters: Preventing corrosion preserves both expensive knives and your dishwasher’s racks, saving up to €150 in early replacements [Consumer Reports, 2021].

Quick Facts

• Ideal wash temperature for corrosion-prone cutlery: 45–50 °C Eco cycle [EU Ecodesign, 2019]. • Recommended water hardness setting: 4–7 °dH (soft) [Bosch Manual, 2023]. • 18/10 stainless contains 18 % Cr and 10 % Ni—gives 2× higher pitting resistance than 18/0 steel [Stahlwissen, 2022]. • Rust-spot removal paste costs approx. €6 per 75 ml and lasts ~40 knives [Amazon Prices, 2024]. • Replacement rack-tine caps: ~€5 for 100 pcs, stop rack-borne rust migration [Amazon Prices, 2024].

1. Why did rust spots appear after two rust-free years?

Two triggers changed: a salt-cap that no longer sealed and a dirtier filter system, raising chloride and iron levels that attack micro-defects in the steel surface [Elektroda, Mateusz_konstruktor, #20119606; Elektroda, pilomatt, #20119264]. Carbon-lean stainless delays, but does not stop, such pitting once chlorides exceed ≈150 ppm [BAM, 2019].

2. Can a leaking salt container really corrode cutlery?

Yes. Undissolved salt grains or brine splashes create local chloride concentrations >10 000 ppm. Lab tests show pitting after 30 min at 60 °C under such spots [Stahlwissen, 2022]. Users observed stains whenever the cap was loose [Elektroda, pilomatt, post #20119264]

3. How much water and salt should be in the softener reservoir?

Fill salt, then add tap water until the level reaches the neck, leaving ~1 cm air gap to allow thermal expansion [Bosch Manual, 2023]. Overflow on opening indicates over-filling or trapped air [Elektroda, Mateusz_konstruktor, post #20119776]

5. Does program temperature influence corrosion rate?

Lowering wash temperature from 65 °C to 50 °C cuts stainless weight loss by about 40 % over 500 cycles [BAM, 2019]. Users who switched to Eco (≈50 °C) saw fewer new pits [Elektroda, Janusz_kk, post #20120652]

6. Are “rust magnets” or aluminium blocks effective?

Tests show no meaningful difference; the aluminium block itself rusted after five cycles [Elektroda, mipix, post #20127539] No peer-reviewed study supports magnetic rust capture in dishwashers.

7. Will buying 18/10 or acid-resistant cutlery eliminate spots?

18/10 stainless resists household chlorides up to 2 000 ppm; cheaper 13/0 steel pits above 300 ppm [Stahlwissen, 2022]. Switching grades therefore greatly reduces, but cannot fully eliminate, stains when salt or detergent misuse occurs.

8. How can I remove existing rust safely?

Use a non-abrasive paste (citric acid + silica). 1. Apply thin film for 3 min. 2. Rub with microfibre. 3. Rinse and dry. Avoid steel wool; it deposits free iron that re-rusts [NSF, 2020].

9. What if my basket coating is cracked?

Exposed carbon steel racks leach rust particles that redeposit on cutlery. Clip-on vinyl caps or liquid racking repair stop the transfer and cost <€10 [Amazon Prices, 2024]. Check wires monthly [Elektroda, William Bonawentura, post #20121316]

10. Do mixed-metal loads (e.g., aluminium pot + steel cutlery) speed up corrosion?

Yes. Aluminium forms the anode in chloride solution, accelerating steel pitting by up to 3× in ASTM G71 tests [NACE, 2018]. Forum users noted heavier residue when Al items were present [Elektroda, viayner, post #20127967]

11. Is a vinegar rinse useful for dishwashers run only bi-weekly?

Adding 100 ml of 5 % vinegar after the last drain suppresses bacterial bio-film and neutralises alkali, which users report prevents odours and stains [Elektroda, Janusz_kk, post #20120011]

12. How do I set the correct water hardness on my machine?

Consult the manual menu and match local hardness: 0–7 °dH set level 1, 8–14 °dH level 2, etc. Municipal reports list hardness; test strips cost €4 [Bosch Manual, 2023]. Wrong setting wastes salt and increases chloride load.
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