Iodine-Thiosulphate Sequence
To Remove Mercury Pigment


Solution A
Iodine 1 g
Potassium iodide 2 g
Distilled water 300 mL
Mix the dry iodine and potassium iodide.
Add 5 millilitres of water and swirl until dissolved.
Add the rest of the water.
Solution B
Sodium thiosulphate 3 g
Distilled water 100 mL

Tissue sample
Use on sections fixed with a solution containing mercuric chloride.


  1. Bring sections to water by an appropriate method.
  2. Place into solution A for five minutes.
  3. Rinse well with water.
  4. Place into solution B for a few minutes until the tissue is bleached.
  5. Wash in water.
  6. Continue with the main stain.

Expected results
Mercury pigment is removed.


  1. The iodine solution given is Gram's iodine formula. Almost any other iodine solution will be satisfactory. Some technologists prefer to use a 0.1% alcoholic solution (tincture) of iodine.



Drury, R.A.B. and Wallington, E.A., (1980)
Carleton's histological technique Ed. 5
Oxford University Press, Oxford, UK.

Almost every reference text will include details of the iodine-thiosulphate sequence.




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