At 9:52 am (PDT) Sun Oct 8, 2006, adriano-sar wrote:
>At 5:44 am (PDT) Tue Oct 3, 2006 leon_heller wrote:
> > I was curious about the stuff sold for removing ferric chloride
> > stains...oxalic acid crystals and rubbing with rhubarb leaves
> > should work just as well, they contain oxalic acid.
> > Its quite poisonous, BTW.
>
>use the muriatic acid with hydrogen peroxide and does not remain
>residual, once used it is neutralized with of common bicarbonate
Fisio, if you look back in the message archive you will see that
this thread is for people who already have ferric stains and would
like to be rid of them.
They have already been advised that there are cleaner etchants.
If you really mean to recommend HCl+HOOH as a stain remover,
isn't this just a little bit aggressive for the task? (It will attack
natural fibres and most common metals.)
I would endorse the use of oxalic acid.
Apart from its toxicity by ingestion, it is a relatively harmless
fruit acid. As such, it is easily mistaken for ordinary culinary
ingredients such as citric acid or cream of tartar [potassium
hydrogen tartrate]. If you buy in bulk make sure it is labelled
clearly and not stored near foodstuffs.
It is the active ingredient in the "Stain Devil" rust stain remover,
which comes in safety packaging.
The toxicity is because calcium oxalate is not very soluble.
Once the oxalic acid has been absorbed from the gut it
combines with calcium ions in the blood to form a precipitate
which clogs the kidneys, leading to kidney failure. Hence
the occasional poisonings of the ignorant or starving by
rhubarb leaves. The stems contain much less oxalic
acid and are delicious and safe to eat. Even so, I prefer
to eat mine with evaporated milk, just to be sure the residual
oxalic acid is bound in my gut rather than my bloodstream.
As a stain remover, rhubarb leaves seem a good way of
replacing ferric stains with chlorophyll stains ;-)
(NB: chlorophyll dissolves in alcohol or bio-detergents.)
Oxalic acid acts as a mild reducing agent and converts the
brown ferric ion to pale green ferrous. I'm guessing the
ferrous ion is more water-soluble than ferric.
Other common chemicals which _might_ work are:-
∗ citric acid [lemon juice], (nowadays used in preference to chromic
acid to pickle new stainless steel to remove surface free iron);
∗ cream of tartar + glucose, (the kind of slow reducing agent used
to deposit silver mirrors); or
∗ acetic acid [vinegar], (acetates are often very soluble).
None is specially toxic and they might already be in your kitchen.
Perhaps Mycroft would care to comment on these suggestions?
Regards, LenW