Louise Renton in South Africa requests info on formic acid based decalcifying solution for subsequent IHC. She puts "grovelling" after her name, because she probably realises we discussed this last week on the Histonet! 
This is Gooding & Stewarts  formula. I don't have the original reference, but it is in my 1968 edition of "Handbook of Histological Technques" by C.F.A. Culling (2ed edition) I used when I trained in London:
 
Formic acid ...5-25 ml
Formaldehyde (40%)...5 ml
Distilled water... to 100 ml.
 
We use it at the 25 ml strength and it works just fine, not really fast like RDO, but fast enough!
 
(Happy fourth of July)
 
Mike Titford
USA Pathology
Mobile AL USA
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