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Sulphiding - oxidising silver


#1

G’day. My statements that blackening silver with chemicals like
’liver of sulphur’ is NOT oxidation have recently been questioned.
Damn! I knew I would be taken to account one day for that comment!
So I think I’d better explain.

You see, my object when answering chemistry oriented questions is to
keep the answer as simple and jargon free as possible, with clarity
and minimum symbolism foremost. In my enthusiasm for this style of
explanation, I have NOT been academically correct when I have said
that using liver of sulphur or lime sulphur to blacken silver is NOT
oxidation. So I’d better come clean.

Chemistry states that the process called oxidation occurs when:-

  1. Oxygen is combined with a substance. eg. (Oxygen to iron =
    iron oxide: heat with air.

  2. Electrons are removed from a metal.

  3. A non-metal is made to combine with a metal eg. (sulphur to
    silver = silver sulphide;) add potassium polysulphide - ‘liver of
    sulphur’ eg. (sulphur to oxygen = sulphur dioxide;) burn in air
    Thus you will see that the process of blackening silver by coating it
    with a thin layer of silver sulphide, IS an oxidation process, and
    there the confusion may lie as no oxygen is involved. So I much
    prefer to use the word “sulphiding” which I believe leads to less
    confusion. Actually, it is all academic anyway, and what one calls it
    makes no difference to the practical results. I’m talking mostly to
    jewellers, lapidaries, metalsmiths, etc, NOT chemists!

I should therefore parade down the street in sackcloth and ashes,
shouting “Mea culpa!” But as we use a heat pump which doesn’t produce
proper ashes, and our sacks are of woven plastic I’ll have to
forego that public exhibition of remorse. I apologise to those whom
my comments have led astray.–

Cheers for now,
JohnB of Mapua, Nelson NZ


#2

John, thanks so much for that wonderful exposition on "sulphiding"
vs. oxidation! There are those of us who love those kinds of
details --keep 'em coming! It was a help to me, because I was
feeling that guilt about calling chemical reactions not involving
oxides, “oxidation.” You have lifted a tiny burden from my
shoulders!

Judy Bjorkman