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Rust spots on stainless steel in dishwasher

The manufacturers of our left-handed kitchen knives claim they are dishwasher safe and that the handles and blades will not be harmed by putting them in a dishwasher.   We test this ourselves and regularly dishwash the knives we use use in our own kitchen and have not had any problems.   However, we do get occasional reports from customers of small rust spots developing on their knife blades so we have looked into this and found out the following:

  • Dishwashers can sometimes cause rust spots on stainless steel surfaces because of a combination of the levels and types of salt, rinse-aid and dishwasher tablets used.
  • The biggest factor seems to be having too high a level of salt in the machine, particularly when using multi-function tablets that can contain salt themselves as well as what you put separately into the water softener.
  • There are such a huge variety of dishwashers, cleaning programmes and consumables as well as large variations in the softness of local water that it is very difficult to give a single recommendation on how to avoid it.
  • Reducing the rate at which your machine uses salt, while still cleaning effectively, is a good thing to do anyway and the manual for your machine will tell you how to adjust the flow rate.
  • Removing the knives from the dishwasher soon after it finishes will also help, as being in the steamy damp environment for a long time can also cause rust spots.
  • Rubbing the knife blades with a slice of lemon occasionally can help reduce the problem.
  • If you do get rust spots, they should be easy to remove with a scourer, a stainless steel cleaner or with some car chrome polish.

It does seem this can happen to any stainless steel if there is a combination of the factors above so we cannot absolutely guarantee that our knives will never develop rust spots under any conditions and you may need to adjust the salt usage or other factors in your dishwasher to avoid it happening.

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8 comments on “Rust spots on stainless steel in dishwasher
  1. Krista Welton says:

    What could cause this if you use fresh water, no water softener is used.

  2. Ray hope says:

    Thank you, what you have said makes complete sense tome, so I’m going to remove my knives and forks as soon as the washing machine finishes and just leave the dishes behind to heat dry, regards Ray

  3. Ray hope says:

    What absolute nonsense! If you have to clean the rust spots off with a scorer, why bother to put them in the dishwasher in the first place! Can we have someone from the manufactures to give us the correct answer instead of clever dicks with no real understanding of how these machines work! I’v a brand new Bosch dishwasher and at no time did Bosch tell me in their brochure and advertising campaign that I would have to clean these rust like spots from my knifes and forks. I wash exactly the same way every time, sometimes there like new other times there marked! I’m thinking that I will give it back as ‘not fit for purpose’ and reclaim my money back! So let’s get on to Bosch etc! And give them the problem of finding out what’s going on!! My old cheap machine that was second hand, that ran for 10yrs in my kitchen, NEVER gave me rusty marks! There’s got to be an answer and its up to the manufacture to sort it out!

    • Melinda hughes says:

      I’m having the same exact problem with my Samsung stainless steel dishwasher! Washed my knifes for years in a cheap plastic rubbed dishwasher, now with the new stainless steel rubbed Samsung, my knives are starting to rust!

    • Fed up Totally says:

      74NZ I have found that my 5 month old Bosch dishwasher only cleans glasses, plates and dishes. Pans: white ring is left and it fails (eg) to remove orange deposit left from boiling carrots; stainless steel cutlery has become v stained as have sieves or other ss objects. It cannot clean cups/mugs and they have to be SCOURED vigorously to be stain free. Coffee/tea cups/ mugs NEVER failed to be clean in my 3 previous dishwashers. I’m at a loss. Just don’t know what to do! Engineer visit pretty useless. Use Quantum Finish tabs! Good grief! At £12 a smallish pack!! Why don’t Bosch tell you their dishwasher is only effective with top of range tablets. I’m trying a Finish additive. If it doesn’t work will ask for a refund. If it can’t clean dishes it is not a dishwasher.
      Very disillusioned pensioner Bosch dishwasher user. Hundreds of pounds spent and I have to rewash dishes. Not progress. Not acceptable.

  4. Ken Toll says:

    I have had this problem with stainless steel cutlery from another supplier for a very long time 🙁

    I was told it was due to silver contamination of the dishwasher, caused when an old EPNS spoon was inadvertently put in the dishwasher. Apparently Silver acts as a catalyst and remains in the dishwasher to contaminate other stainless Steel items. Best advise was not to leave damp cutlery in the dishwasher for prolonged periods.

    See: https://www.arthurprice.com/page/care

    HTH,

    Ken

  5. Steve Lockley says:

    This is a technical tip from our website, eriks.co.uk, regarding stainless steel:

    Stainless steel has the property of not rusting. However, if tools made out of conventional steel are used for stainless steel components or screws, the particles left behind from these tools can adhere to the surface and then rust. This effect – known as extraneous rust – can impair the visual appearance and even cause structural damage which may result in expensive repair work.

    The wear particles that cause this rust effect can be prevented by using stainless steel tools. The same applies in reverse when using a stainless steel tool on a ferrous fastener or component.

    I presume that what applies to the stainless steel bearings and tools we supply also applies to cutlery. So the lesson is to keep your stainless steel implements separate from ordinary iron and steel wares as far as possible

    Hope this is interesting to you

    • Mark. says:

      My dishwasher leaves rusty marks on my stainless items. I think the problem was caused by a set of stainless pans I bought that had normal steel screws holding the handles on. The pans were stainless steel, the handles were also, but the screws holding the two together were defiantly not stainless. Really irritating, as 2 years after I threw away the pans with the rusting screws I still get rust marks. Anyone able to suggest something that can be put into a dishwasher that will remove the minute rust particles let behind?

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