Re: Warthin-Starry Addendum

From:"J. A. Kiernan" <>

On Mon, 6 Nov 2000 wrote:

> I have found mention in literature of a post treatment using a 1% aqueous 
> potassium ferricyanide solution to reduce background staining after the 
> Warthin-Starry technique. It may also be helpful!
> J.D., Bancroft, Theory and Practice of Histological Techniques, 3rd ed., 
> Churchill Livingstone, Inc., January  1990.

    Potassium ferricyanide oxidizes silver (coloured or black
    colloidal metal) to silver ferrocyanide (a white insoluble 
    solid that can be dissolved by a solution containing sodium
    thiosulphate). The ferricyanide and thiosulphate are
    combined in the same solution in Farmer's reducer,
    which is used to lighten overexposed black & white
    negatives or prints. Reduction, in this context, means
    reducing the amount of silver in an image. (Chemically
    speaking, this is oxidation, not reduction!) Farmer's
    reducer or a similar mixture can be used to lighten
    any silver staining method.

    Ferricyanide acts first on the smallest silver particles
    in a stained section or smear. This can clear a yellow
    or light brown background. The largest colloidal silver 
    particles (black) are the last to be extracted. The
    method will not work on preparations that have been

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

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