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Quince
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Removing stainless steel lining from copper cookware
I have a small set of that French copper cookware, that I bought off eBay for a decent price (nice too, 2.5 mm thick copper), but instead of the
common ones which are tinned on the inside, I got the ones that have a stainless steel lining instead, due to availability. Well, stainless steel
sucks for cooking! Food sticks on it really bad, especially the frying pan.
There's a place I can take them where they re-tin cookware with worn tinning, but want to get the stainless lining off first with minimal damage
to the copper, as the guy said it has to be either bare copper or tin when he's working it. Is there any chemical and/or electrochemical method
I can use to do that? (the lining is a fraction of a mm)
[Edited on 15-3-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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12AX7
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Well, theoretically you could use the difference in ionization voltage, but the protective chromium oxide layer is going to thwart any attempts.
Maybe an acid that eats CrO2 (Cr2O3?) and not Cu?
Or just go the easier route and get a sheet of heavy copper and bash a frying pan out with a hammer and sack of sand.
Tim
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Quince
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The easier route is no fun, plus, it will look like crap. Yes, looks matter, else it wouldn't have cost that much.
I am curious as to how the stainless steel is bonded to copper ("bonded" is the word they use, not plated or something like that).
So no one can think of a substance that would more readily attack stainless steel than copper?
Maybe I could just monitor the thing carefully and pour the acid out when it starts showing copper, and then apply locally to any steel left, or just
use a polishing wheel with fine grit paste. But I need to leave a surface that will allow the tin to take hold.
What about using electrolysis to speed it up?
Edit: in testing, heated HCL+peroxide works (very slowly), but that will destroy the copper too.
[Edited on 15-3-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Theoretic
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You could carefully choose the electrolysis voltage so that it's enough to dissolve iron but not enough to damage the copper.
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Quince
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Interesting. What electrolyte do you recommend? Do you think the fact that there are other things than iron in the steel make a difference in
voltage?
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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neutrino
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Stainless steel is not entirely iron; it is mostly other metals. If you go by electrolysis, make sure to thoroughly wash the pan before using it, as
salts of some of the metals are not good for you. I’m not sure how much of these chemicals you’d get forming, but this is something I’d keep in
mind.
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Mr. Wizard
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Since the stainless steel is thick, strong, and obviously the strongest part of the pan, why don't you just overcome the problem of sticking by
copper plating the inside of the pan and tinning it? You might even get some silver solder to stick to the stainless, and then you could put on a nice
thick tin wipe over the silver solder. Make sure the silver solder you choose doesn't have lead or cadmium in it. You'll have to use an
appropriate flux to get the intermediate silver solder to stick to the stainless. These usually contain some fluorides or Zinc Chloride. Any mistakes
can be buffed off ;-)
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Quince
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Mr. Wizard, you got it backwards. As I wrote in my first post, the copper is 2.5 mm thick, whereas the stainless steel is merely a lining (acidic
foods corrode copper and some ends up in the food, so bare copper can only be used in non-heat non-acidic stuff in the kitchen) -- fraction of a
millimeter thick.
Copper has to do with far more than just looks. Its thermal conductivity is around double that of aluminum, and several times that of steel. Putting
a stainless steel lining is thus pretty stupid, even though it's thin; tin is not much better than steel, but the layer is thinner. Still, even
with the stainless steel, cooking with these definitely makes a difference (I've also used aluminum, cast iron, and stainless steel; I don't
use Teflon as the first scratch means shit released into the food).
[Edited on 16-3-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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12AX7
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| Quote: | Originally posted by QuinceI don't use Teflon as the first scratch means shit released into the food.
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Well, inert shit, that then passes through you to be released stuck in your, uh, shit. (Gee, thanks for bringing up that word and ruining my sentence
 )
Cast iron owns you, frying pans, machine tools, what next! 
(Yes, informative post of the year award  )
Tim
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Mr. Wizard
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Sorry about the mix up. I don't know of any way to remove the stainless steel from the copper. Maybe a grinder or a sanding machine. I realize
the copper is a much better conductor of heat than stainless, but on thinking about it, wouldn't a slight resistance to the heat flow
allow the copper to spread the heat around a little more? How well do the pans work, other than the sticking problem? Just curious.
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Quince
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12AX7, you are wrong. It is not inert even at some of the cooking temperatures that the pan can reach (260*C by DuPont's own admission produces
polymer fume fever). Also see several comments at http://www.mercola.com/2001/aug/1/teflon.htm and note the last comment by Howard about the toxicity of ultrafine Teflon particulates. If you want
a cheap pan that doesn't stick, just use cast iron. The weight will only help you get muscles  (don't forget that cast iron must be primed by oiling and baking first when new, and never stored wet, but
reoiled)
Mr. Wizard, as I said, "cooking with these definitely makes a difference". I like my cookware to react fast to any change in the heat (I
use a gas stove, of course). Even with the thickness of the copper, I still get that. Many professional chefs use copper, especially the French (but
I'm not French)
A warning: some people don't expect it, but copper oxidizes, so there's no way they will maintain the salmon-pink color when they are
actually used instead of just sitting around. The copper oxides that form on the surface turn all sorts of funky colors, like
brown/green/blue/orange/purple/yellow. You can use ketchup or copper restorer or Barkeeper's Friend etc. to return to the original color, but I
don't bother.
Also, depending on thickness, they are heavy, though not as heavy as cast iron. Flipping pancakes is probably out of the question
BTW, they can't be used on induction stove, don't know why, maybe something to do with two metals bonded together.
If you are patient, you can find them new on eBay for as little as half price. Worst place to buy is locally (not online), as far as price. Within
about ten years tinned ones will need retinning (if you use them regularly). But I think it's worth it if you are serious about cooking.
[Edited on 16-3-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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12AX7
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"A standard method of producing an aerosol of ultrafine particles is to heat PTFE up to 480°C. This produces some gas-phase products, mainly HF
(hydrogen fluoride)."
Even 500°F (260°C, hm the farenheit number is more asthetic, I bet the number has a wide tolerance) is pretty hot for frying. If you have
respiritory problems, the small amount of fluorides amongst the plumes of smoking fat are the least of your worries.
But that's off topic...
Fast response is a good point, I get used to it and change the burner before I need it  but I'll have to make a copper pan some day, heck maybe tin it myself, we'll see.
Probably can't be used on induction because the copper is too conductive and doesn't load the stove properly.
Tim
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Saerynide
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That seems like a lot of work for a frying pan (considering how heavy it would be to cook with as well). You must be a really good cook then to
appreciate it so much
I, on the other hand, would just stick to aluminum or like 12AX7 said, just hammer out my own
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Quince
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Well, my set of a pan and two pots is worth about $800 Canadian retail price (I bought them far cheaper at auctions). You'd think that's
crazy, but I love them!
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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unionised
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Last time I checked copper was a noble metal and iron, chromium and nickel were not. In principle any (non oxidising) acid would work.
Stainless resists some acids quite well, but HCl rots it reasonably quickly. You want to put some sort of a lid over it (perhaps clingfilm) to keep
the air out. (HCl and air will attack the copper.)
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Quince
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I know the air problem. Is there any oily substance that will resist HCL (lighter than the acid and not miscible with it), so that I can pour a thin
air-blocking layer on top of the acid? Can I speed the process up with electrolysis?
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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chemoleo
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Common Quince, that really isn't so hard. Paraffin will do the job. Lamp oil. whatever.
Electrolyis will result in dissolution of the copper as well. The surface won't be good, you will have lots of holes etc.
Just do it as he suggests, dump it into HCl, put it on the radiator and leave it there for days/weeks until the steel is gone. It won't be fast.
But electrolysis is almost certainly no good. So what options are left? Not many.
So how many questions are you going to ask now?
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Twospoons
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If you heat the whole thing to about 800C, then cool very slowly, most of the chromium ends up as the carbide, and the stainless property is lost.
Unless its a welding grade stainless. At any rate, leaving the whole thing submerged in brine would preferentially corrode the iron, thanks to the
electrolytic couple formed between the copper and the iron. (or have I got my electrochemical series backwards?)
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Quince
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| Quote: | Originally posted by chemoleo
So how many questions are you going to ask now? |
Just one: when are you going to stop being such an asshole? Oh wait, I already know the answer to that.
Twospoons, I'd test the brine soaking on a piece of steel and copper, but I don't know how to bond them together so that there isn't a
reaction between the contact point of the materials. Will a solder joint (out of solution) between them invalidate the test due to the introduction
of a third material?
[Edited on 17-3-2005 by Quince]
\"One of the surest signs of Conrad\'s genius is that women dislike his books.\" --George Orwell
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Twospoons
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A solder joint out of the brine will be just fine. This is just a simple battery cell after all.
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mick
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I have a small set of that French copper cookware, that I bought off eBay for a decent price (nice too, 2.5 mm thick copper), but instead of the
common ones which are tinned on the inside, I got the ones that have a stainless steel lining instead, due to availability. Well, stainless steel
sucks for cooking! Food sticks on it really bad, especially the frying pan.
I have a nice set of cast iron cooking equipment. A good quality SS frying pan is OK. The one I had was non-stick untill some one cleaned it with a
scouring pad.
mick
Chloride seems to corrode stainless steel
mick
[Edited on 17-3-2005 by mick]
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Theoretic
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neutrino, stainless steel is mostly iron, which is why it's called steel.
chemoleo, read my post carefully, I said a voltage low enough not to dissolve copper while still dissolving the iron. I recommend... well, most
electrolytes will do, a salt solution too.
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neutrino
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If you’ll notice, most of the steels on your site have a lot of nickel in them. Nickel salts being carcinogenic, it would be a good idea to be
careful with any chemical process.
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unionised
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" Is there any oily substance that will resist HCL "
Most oils would do. Given that this is for cooking I would try cooking oil, it might hydrolyse a bit but you can be reasonably sure that you
won't get any toxic products from it.
OTOH, by the time you have washed away the chrome and nickel salts, you will have got rid of most things.
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chemoleo
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| Quote: |
Just one: when are you going to stop being such an asshole? |
If I wasn't being an 'asshole' you'd flood the forum even more with trivial/repetitive/post-whoring and attention-seeking
questions, laced with avoidable inaccuracies here and there (remember the xenon thread?). It all serves a purpose. Just in case you failed to realise
that. You weren't warned numerous times for no reasons.
Theoretic - about the low voltage - sounds like a good idea in principle, but I doubt it would work well in practise. The solution would have to
conduct very well to enable a decent current density for decent iron dissolution. But it's worth a try I guess.
The potentials are
Iron= -0.44 V
Nickel = -0.24 V
Tin = -0.14 V
Lead = -0.13 V
Hydrogen = 0.00 V
Copper = +0.34 V
At i.e 0.5 V & 20 W power (which isn't much), the solution cell would have to conduct 40 Amps, at a resistance of 0.0125 ohms. Rather hard to
achieve I should think. Might be just easier to dissolve the damn thing in HCl. But I am not Mr electrochemical here, so correct me if I am wrong.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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