[Jewelry making - Article 00442] - Re: [Orchid] Sulfides & sulfates

[John Burgess]

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>        blackening ('oxidizing') silver? 

    G'day;  Sulfates (sulphates)  Do not, either in theory or in
    practice, blacken silver. In any case, The blackening of silver by
    the use of sulphides is not oxidation, (other than in a very
    academic sense which doesn't concern us here) but the conversion of
    the surface of the silver into silver sulphide which is black.  
    Silver oxide is not black, but an off-white colour, and is difficult
    to produce.   Sterling silver, because it contains copper, does
    blacken on heating in air due to the formation of copper oxides,
    which can be removed by weak acids, such as sodium or potassium
    bisulphAte, not sulphIde or sulphiTe So I am afraid I disagree with
    Carles Codina. _as quoted;_ but perhaps the truth was lost in a 
    translation? -- 

Cheers for now,
John Burgess;   johnb AT ts.co.nz of Mapua, Nelson NZ


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