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I live in the USA and have one of these stoves:

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For me who comes from Europe, the design of these stove tops always baffles me compared to flat (metal or glass) stove tops seen across Europe (it seems to be losing a more energy, the materials rust easily, and it's always so hard to clean!). Today, I met with this strange situation where the cup under the coil, after I cleaned it, started showing scary blue spots:

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Although these marks are very photogenic, I am afraid that they might be Verdigris.

Is it possible that the material used in stove cups would be that easily corroded that it actually produces poisonous substances such as Verdigris when cleaned?

Obviously this one is a bit old and might need changing - probably for one that is made out of a material that doesn't corrode that easily (I love spending money on this stuff! ❤️ ), but if someone can confirm that these stains are not dangerous, I'll try and make it last a little longer. At least till I find a really cheap one that is rustproof on eBay (since I'm not really keen on giving to this "bad design makes the end user waste money having to fix stuff" philosophy).

Thank you for your help!

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    Not dangerous, unless you scrape that stuff off and snort it or eat it,. Just scrub the things with steel wool and hot soapy water and put them back on. The food you actually eat is probably more dangerous. – Jimmy Fix-it Apr 28 '16 at 2:31
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    These are for rental units. Tenants tend to treat glasstops roughly (not least by using the wrong pots and pans). These are easy to keep nice: change the drip pans ($3-5 each) and any nasty heating elements, and the stove is "good as new". A tenant in a hurry to get his deposit back will often run out and buy cheap or ill-fitting ones like the above. Homeowners do typically get glasstops. Anyway, yours are chrome plated steel - they're rusted. Rust only happens to iron and steel (more the latter). Just buy new ones. amzn.to/1rmtWZf – Harper Apr 29 '16 at 5:03
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    Right, it's just the lowest-end electric range. There are better ones. You can buy one if you're the owner. If you;re the renter, you can always ask the landlord. It's possible they'll give you a break on rent that month if you buy one. – iLikeDirt Apr 29 '16 at 13:49
  • A break on rent, you mean allow me to deduce the price of what I paid for it from the rent, right, I don't think they'd have me not pay the rent because I bought a $5 stove cup lol – MicroMachine Apr 29 '16 at 18:22
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    No one makes drip pans out of copper. The stuff is too expensive, and its heat conductivity would just be a waste there. Plus, it bends easily. You've probably got some funny colored steel or chrome oxides there. – Wayfaring Stranger Apr 29 '16 at 22:20
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I'm a little skeptical because of how purple those stains are, but if these drip pans are made of copper then it could well be Verdigris. This is likely happening because the plates were not sealed properly and vegetable oil was spilled and not cleaned off as heat was applied over time.

If I were you I'd scrape some off (it's OK if some powder comes into contact with your skin once or twice) and set it on a paper towel somewhere. It should turn brilliant forest green over the next couple of weeks if that's the case. While you wait, you can take aluminum foil and wrap the drip pans in them; this is a common technique to help with keeping them clean/protected. The foil wont burn and can be unwrapped and tossed in the trash when you get marks or tears in it.

The danger is really up to your level of tolerance: you'd probably be safe by just cleaning them and the putting them back in; it's only toxic if you ingest the actual substance over time or once in large quantities. You'd almost definitely be safe if you wrapped them in aluminum foil. But if 100% peace of mind is what you're after, I'd ditch them and get new ones; it won't cost you much to get four new Chrome drip pans (maybe $10 to $15).

As far as I know, most drip pans are made of Chrome these days and are not susceptible to the same problem.

If you're up for some more reading, you can check out this ISCA Report on copper and its toxicity.

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Try a magnet - dollars to doughnuts, those are somewhat peeled and rusted chrome plated steel, and the blue is a normal steel oxidation color, and not toxic (also, were you planning to drip food down there, scrape it off and then eat it? If not, nothing to worry about regardless.) They are stunningly unlikely to be copper, though there may be a minuscule amount of copper plating as part of the chrome plating process

This is reinforced by the purple color, which is a slightly different temperature in the steel oxidation colors (we use them for determining temperature when tempering hardened steel.)

steel oxidation colors

Image from Maille Artisans International League website

While you could waste money and effort replacing them, you could also make them more efficient (reflect heat better) and easier to clean by applying aluminum foil to them (shiny side up - you want to reflect as much heat as possible.) As a side effect this would also contain the non-toxic steel oxidation. When something is too badly burnt onto the aluminum foil, remove it and replace with new foil. Mold the foil to the pan, wrapping over the edges - cut stars in the openings and fold the cut parts onto the backside.

FYI - stainless steel will also blue, at slightly different temperatures.

  • Hahah, well of course I wasn't gonna eat food that touched this, but sometimes when you're busy in the kitchen it's better to have a free mindset and go about preparing the food rather than be worried because you might or might not have touched something toxic prior to peeling carrots :P Thanks for the great tip, although wrapping aluminium foil around the cups seems it would produce a less than aesthetic result :D – MicroMachine Apr 28 '16 at 21:57
  • Looks perfectly nice if you mold it to the reflector (not too difficult to do.) If you want to do a bad job I'm sure you can make it look bad, but it looks (and more importantly, as a heat reflector, functions) much better than rusty, crusty chrome (and actually functions better than chrome, period, even if the chrome is shiny and new.) – Ecnerwal Apr 29 '16 at 1:49
  • Ok, I get it. Thanks for the input. We're not here to debate, but I just thought questionable the quality of a design that implies that to make it function better, the user should tinker with it, wrapping parts of it with foil. Seems user-unfriendly, if not a bit archaic considering this design, used in many other countries. – MicroMachine Apr 29 '16 at 18:20
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Edit3: Bleach will react with copper to produce copper hydroxychloride and as wikipedia says, is commonly found in metal corrosion products. Iron (II) chloride is often greenish colored. Iron and copper chloride will react to produce iron chloride.

Looks like bornite (Cu5FeS4) (yes, bornite is toxic too). But it's unlikley, unless someone spilled some sulfur in the mix. It's definitely a copper mineral of some kind... copper is very commonly used when plating chrome.

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Revised answer:

The cups are chrome plated steel. Usually chrome plating starts with copper plated to to steel, then chrome is attached to the copper layer. There may also be other trace metals including nickel, cobalt, tungsten, and zinc.

Why do they plate the cups with chrome? Because chrome plating is shiny (and shiny means it reflects heat better than stainless steel; and chrome is more resistant to corrosion and heat discoloration than steel (actually stainless steel has chrome and other minerals to impart the "stainless" qualities).

Steel will easily discolor (especially stainless steel) when it is heated (like Ecnerwal showed in the picture). However, the discoloration that I see in the picture of your cup is not at all similar to the discoloration of heated steel. The colors of your cup look like distinct "minerals" thact could be scraped off into a bag and analysed by a laboratory.

The brightness of the blue completely suggests a mineral comprised of copper. The location of the colored minerals is another strong indicator that this is a chemical reaction; the minerals were formed in areas of corrosion/oxidation where copper and iron, and possibly nickel and zinc are present. The "peacock" coloration suggests sulfur is/was also present. Sulfur may have come from garlic and onions, or possibly residues from sulfuric acid were present from the plating process, if nickel was used as well.

Edit2 - Other acids will also combine with copper to form other minerals. Many cleaners or "rust emovers" contain phosphoric acid, which could make a form of cornetite (a copper phosphorous mineral) which is darker blue and purple.

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Azurite (a copper carbon mineral) is usually more blue than purplish. Malachite (another copper carbon) has just a couple extra % copper than azurite

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Cuprite + delefossite (CuFeO2 or Cu1+Fe3+O2) can also yield purples and blues.

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So in essence what I'm saying is that this is that copper imparts the blue and or green, and it can combine with iron to make purples, but sulfur really brings out the "peacock" colors. The blue is copper that has oxidized most likely from acidic cleaners.

  • Well, I cleaned it using some sort of bleach / peroxyde. Anything's possible... Why don't they just make them stainless steel beats me. – MicroMachine Apr 27 '16 at 22:55
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    @fabriced I made some edits to my post. the reason that stainless is not used is because stainless doesn't reflect heat as well as chrome, and stainless will discolor an lose integrity too quickly. Chrome is much more more resiliant. – Ben Welborn Apr 28 '16 at 17:53
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    @fabriced I know chemistry. It's copper oxidation, but I wouldn't call it verdigris - which better known as, patina. Copper has been exposed and now it is reacting with iron, oxygen and other trace minerals from food and cleaners. The purplish colors are comming primarily from the iron. But you have a hodgepode of minerals there- which the normal way that it happens- as minerals form. Pure minerals are prized (in part) for their rarity. Hopefully my post above will convince you that you have mineral formation, most lilkey caused by an acid cleaner, in the presence of heat. – Ben Welborn Apr 28 '16 at 20:47
  • @fabriced I actually have the tools and equipment to analyze this... and give a perfectly precise answer, but I wouldn't dare give my address on a public forum. It's a shame. – Ben Welborn Apr 28 '16 at 20:49
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    Great job with the iconography! Now I want to go and buy beautiful blue stones... No need making tests I'm sure you could reproduce this oxydation with your own stove cups and after damaging them with maybe oily water that boiled on them once and then cleaning them with peroxided bleach-type household products (can give you the precise ingredients if you need!) – MicroMachine Apr 28 '16 at 22:00

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