In article >,
says...
>
> J. Clarke wrote:
>
> > In article >,
> > says...
> > >
> > > J. Clarke wrote:
> > >
> > > > In article >,
> > > > says...
> > > > >
> > > > > sf wrote:
> > > > >
> > > > > > On 21 Jan 2011 16:05:14 GMT, "Gareth Fimlinson"
> > > > > > > wrote:
> > > > > >
> > > > > > > is anybody familiar with the discoloring of stainless steel
> > > > > > > pots from overheating?
> > > > > > >
> > > > > > > I saw a manual for one that said "damage from overheating is
> > > > > > > instantly recognizable as the stainless steel surface may
> > > > > > > change color producing a golden/brown/blue appearance. This
> > > > > > > is not reversable and cannot be cleaned off. However it
> > > > > > > will not affect performance in any way".
> > > > > > >
> > > > > > > Does this sound familiar to people?
> > > > > >
> > > > > > Yes. That's one of the reasons why I didn't get the mirror
> > > > > > finish when I spent what I consider "real money" on cookware.
> > > > >
> > > > >
> > > > > Any idea what the mirror finish is made of?
> > > > >
> > > > > What the discoloring is.
> > > > >
> > > > > Are there any leakage or health issues with using it after it
> > > > > has discolored?
> > > > >
> > > > > If it can be removed then why does it bother you?
> > > > >
> > > > > What makes make stainless steel pots without the mirror finish?
> > > > >
> > > > > I do want it to be metal inside.
> > > > >
> > > > > Looking at this pot,
> > > > >
> > > > >
> > >
> http://www.lecreuset.co.uk/Product-R...-and-Lid-20cm/
> > > > >
> > > > > the upper side and bottom side of the lid of the pot is very
> > > > > mirror like. I've seen it.. But i'm not sure whether you'd say
> > > > > that of the inside.
> > > > >
> > > > > Has anybody seen discoloring on pots that don't have a mirror
> > > > > like finish? Were people that have seen discoloring on their
> > > > > pots, able to see their face on the surface where the
> > > > > discoloring was? (that would help determine if pots without
> > > > > the mirror finish wouldn't/couldn't ever get discolored from I
> > > > > suppose, the accident of overheating dry).
> > > >
> > > > This isn't anything that is magically related to shiny finishes
> > > > or stainless steel. Heat most steels to around 580F and they'll
> > > > turn blue (don't go quite so high you get yellow, go higher you
> > > > get gray). It's oxidation, it's normal, <snip>
> > >
> > > Any explanation for why poster "sf" found his stains got on the
> > > mirrored parts like the outside?
> >
> > Because that's the part that was at the right temperature?
> > Understand, it's not a matter of "if it gets hot it turns blue",
> > there's a range of colors that indicate the temperature achieved with
> > a fair degree of precision--accurately enough to allow a machinist to
> > temper a part to a desired hardness. Blues come in around 550F and
> > are gone around 600F.
> >
> > > Perhaps he oxidized the outside of the pot ..maybe the gas light was
> > > too big for the pot and heated around the outside of the pot. But
> > > he found this hasn't happened for pots without the mirror finish.
> >
> > Which means that he didn't overheat them, or that he got them above
> > the temperature at which the color is blue, or that he just can't see
> > it on the unpolished surface.
> >
> > > If a metal pot was completely oxidized inside, would it make no
> > > difference at all to cooking food in it?
> >
> > If it's stainless steel it is completely oxidized. Stainless works
> > by forming a tightly bound layer of oxide. Ordinarily that oxide
> > layer is transparent. When heated to a certain temperature it turns
> > blue.
> > > I presume cooking from a rusty pot is a bad idea?
> >
> > If you consider a thin layer of oxide to be "rusty" and find it
> > objectionable, then never use stainless steel.
> >
> > > And the discolored stainless steel pots, are rusty?
> >
> > No rustier than any other stainless steel pots. Only difference is
> > that it's a color that you can see.
>
> suppose the whole pot is stained blue, I suppose it'd just mean the
> surface oxide layer is thicker than it was, and it'd never matter
> beyond aesthetics?

Pretty much.

> what temperature, should I expect the pot to reach if not heating dry?
> and with a gas light.

What are you heating in it? If it's water I'd be surprised if the
surface of the pot got up to 300F. If it's oil it can get very hot--
refined avocado oil has a smoke point of over 500F and the surface of
the pot will be higher than that. The flame itself reaches 3000F at
spots.

> i'm starting to think that with a gas light, staining is almost
> inevitable.

Probably--gas is clean burning but it can still leave deposits.
>
> With my teflon pots i'd stick the gas light to the highest point(but
> without the flame going up the sides of the pot). I guess oxidation
> there might not have happened because the outside was painted and the
> inside was coated.

Is it Teflon on stainless or Teflon on aluminum? If it's aluminum you
won't get the color changes anyway.

> The manual for this pot says to keep the flame between light-medium,
> (and to use a hob that isn't too big, so it doesn't go up the sides of
> the pan)
>
> I see a nice article here on colors of the surface oxide layer, and
> temperatures.
> http://www.bssa.org.uk/topics.php?article=140
> pale yellow(290C), straw yellow, dark yellow, brown, purple brown, dark
> purple, blue, dark blue(600C)

Somebody had their temperature scales confused. Here's one that gives
the range in both C and F <http://www.muggyweld.com/color.html>.