Re: Warthin-Starry Addendum

From:"J. A. Kiernan" <jkiernan@julian.uwo.ca>

On Mon, 6 Nov 2000 Ballnclaw@aol.com 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
    gold-toned.

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




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