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I have a small cast iron pan which I am working with, trying to make sure I understand seasoning/cleaning before moving on to a larger one. I seasoned with flaxseed oil (4 light coats, hour in the oven), and have cooked a few things - I made some Ghee, fried some onions, stuff like that. After each I washed with hot water (no soap), heated until dry on the stove and coated with a thin layer of canola oil.

Now, when I take a dry paper towel and rub it on the pan, a black residue shows up on the paper towel. I can't feel anything with my fingers and I haven't noticed anything cooking with it. I'm fairly confident this occurred after the initial seasoning - although I'm not sure I did this exact test with the paper towel.

Is this a) normal, or b) what is wrong and c) how can I fix it?

There are quite a few questions (and good answers!) regarding cast iron cookware on this site but I haven't been able to find one that deals with this specific issue.

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up vote 3 down vote accepted

You may notice the black residue if you fry eggs in the pan as well.

Most likely, the black residue is charred (greasy) food sticking to the seasoned oil. Since Flaxseed oil has low heat tolerance, it could be that disintegrating, too. Otherwise it could be related to the iron in the cast iron which isn't bad for you (some say even good).

a) Is it normal: Yes if you keep with the same regiment (recommend you don't).

b) What is Wrong: Water won't perfectly wash non-polar chemicals such as burnt solids in grease (milk solids while making ghee), so the hot water no-soap routine leaves the stuff in pan.

c) How can I fix it: Try the following going forward:

  • After you finished cooking and while the pan is somewhat hot, put a heap of salt in the middle and with a paper-towel spread and lightly scrub the pan. The salt will pick up the would-be black stuff, largely disinfect the pan, and the abrasive properties of the salt helps with the cleaning.

  • Wipe off the now brown salt from the pan and rub-in the coat of oil as you normally do. The new coat will stick better to through the salt's abrasive effect.

This routine won't eliminate residue altogether. But it seems to work great long term.

Note on oils: Flaxseed oil is best consumed cold and within three weeks. I haven't heard of a credible source promoting seasoning the pan with flaxseed oil as it has one of the lowest smoke points in the oils. Use a more heat tolerant oil like light (not extra-virgin) olive oil or canola.

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I don't make any claims as to the credibility of this source. However it is one source that suggests using flaxseed oil: sherylcanter.com/wordpress/2010/01/… – johnny Aug 22 '13 at 5:34
    
And that's the source which I used to decide which oil to use. – levitopher Aug 23 '13 at 0:23
    
@levitopher I get her idea on the drying oil that artists used. From what I know flaxseed oil is not temperature tolerant and can form cyclic hydrocarbons or long chains that are carcinogenic at higher temperatures. She doesn't seem to address that part, just says flaxseed oil is the only edible drying oil, therefore ... – MandoMando Aug 23 '13 at 14:07
    
grapeseed oil is a good neutral high-heat oil. – smcg Jan 24 '14 at 16:38
    
@MandoMando is the smoking point strictly relevant to seasoning though? You're pushing the oil way past smoking no matter what type you use are you not? Are you worried that the fumes while seasoning or the carbon layer left behind? – event_jr Aug 10 '14 at 0:51

Although I can't lay claim to what exactly is "normal," I can say that on the occasions that I wipe the cast-iron pan which I use for basically everything on a near-daily basis with a paper towel, it never comes back free of some kind of residue (usually more of a dark brown for me), even after I've cleaned it in the way you describe.

I've been using my pan for years and the presence of this residue hasn't negatively affected pan's effectiveness or the taste of the food that comes out of it, so, I haven't really worried about.

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So as I was surfing the net, I came across this post, and figured I would give my 2 cents. In my experience I have several cast iron pots and pans, also a flat cast iron griddle, dutch ovens, so I am very familiar with these.

I do wash my cast iron in hot soapy water!!!!! But after I wash it I immediately dry it and immediately put on the stove and oil it. Then I tend to put them away.

If I fix dinner in one of my pans, do not wash it immediately, and leave it overnight, I have to wash it the next day. Do not immerse it and let it sit. If you need to get burned stuff off you can also put the stove on and put the pan on it will probably start to burn your already burned on food. Then pour a cup of water in it, be careful it will steam and pop. It will then boil your stuck on food off and come off nicely. You can do this If you do not want to wash in hot soapy water. But I have been washing with hot soapy water for years. My pans do not stick, and are still awesome. It does not ruin them.

If you get your pan washed and seasoned with oil and notice black on your paper towel, keep using paper towels to wipe oil up around sides. Yes you may get paper towel in there initially, but after it's not black anymore you can wipe it out with a damp towel if you wish, then oil once more. Then you are good to go. You will just have to keep oiling and wiping until the black comes out almost clear on the paper towels.

Yes it's time consuming, so be prepared to kill some time and put on your music and wipe oil, wipe oil.

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Welcome to Seasoned Advice and thank you for your first answer. I edited it a bit to hopefully make it easier to read. I wanted to do that because you offer some really good information and I hoped breaking it up a little bit would encourage people to read it. I was happy to give you your first upvote! Check out our tour and help center to get to know us better. – Jolenealaska Feb 23 at 3:23
    
So I am a bit surprised by this, since it's counter to a lot of the advice that I've seen. I have two questions - first, what brand is your cast iron? For instance, I think you could pretty do anything to my Griswold Iron pan and it would work well forever, but submerging my Lodge pans in Soapy water? It would strip them completely. My second question is just that - do your pans actually retain seasoning, or are they just straight silver Iron? – levitopher Feb 23 at 4:32
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@levitopher It is counter to what a lot of us have always been taught; It meshes with something that Serious Eats is putting out. I've been using dish soap on my cast iron for a few months and it's been going great. Seasoning is black as ever (50+ years old). – Jolenealaska Feb 23 at 10:37
    
@Jolenealaska yep, agreed. The no soap on cast iron is a myth. I would never let them soak in soapy water for more than a few minutes, but using soap and rinsing is great for your seasoning. I have forgotten pots in soapy water, it makes a mess. It doesn't ruin the seasoning, but anywhere the seasoning has scratches, rust makes its way through which means heavy scrubbing and a partial re-seasoning session. – Escoce Mar 25 at 15:39

Cast iron when freshly seasoned will not leave a residue on a paper towel.

If you season your pans with flax seed oil, and bake them as instructed, the oil will be bone dry and nothing will come Off on a paper towel.

What you are experiencing is a layer of oil left behind from cooking that has been "partially" dried, and is like that sticky oily goop you get in toaster ovens that is a pain to clean off, but not really a hard substance.

One myth that needs to be debunked is that cast iron and soap should never come in contact. That is simply not true. Another is that you don't use a scrubbing pad on cast iron. That is also not true.

My cleaning regimen, includes using a sponge with a scotch brute pad that has been soaped. I give the entire cooking surface a light scrubbing. Meaning I am not pushing down hard, I am just making sure all the food stuff and un-seasoned oil is removed. I then follow up by putting the pan bake on the stove to dry, wipe the water out, and put a fresh thin coat of oil on the cooking surfaces (up to and including the upper edge). I let it sit on that heat until the oil begins to speckle the bottom of the pan. I wipe those speckles down with a dry paper towel and remove the pan from the heat and hang it or put it on a trivet to cool.

No residue ever comes from this treatment and my cooking surfaces remain baby bottom smooth, even the forge brand skillets.

The scotch brite when used gently knocks down the hills that may develop, without scouring into the valleys. The soap makes sure that all residue and unhardened oil is lifted away from the surface. Laying a new season layer, refills any valleys that may have developed, and wiping the pan out before the speckles can dry assures you are left with a perfectly baby smooth, and residue free surface.

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I just recently got a cast iron small cooking pot, and I seasoned it a bit, and rubbed lard to coat inside, and left it. I used it to broil a small roast, and put vegetables in it, and before this, I washed the lard out, and cooked the roast . Half hour later, I put the vegetables all in, and cooking time is over an hour in total. When I cleaned the pot after cooking, a bit of detergent, and rinsed it good with hot water, then as I wiped it with paper towel, there was black residue, then I rinsed it again and wiped it clean with paper towel, and most of the black residue was gone, and making sure it was dry, I warmed it on the stove, for few minutes, and I felt satisfied it was ready for next time. This is what I do with cast iron frying pans also.

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