The quickest and easiest approach is to view your existing H&E sections 
using a polarized light microscope. Calcium oxalate crystals are 
strongly birefringest and are impossible to miss. Would I be correct to 
assume you have sections of kidney from an ethylene glycol (antifreeze) 
poisoning?

The "stains" suggested in some texts are essentially modifications of 
von Kossa's silver substitution method for  the calcium salts usually 
associated with bone or chronic inflammatory reactions. They work, but 
are not specific for calcium oxalate as they will also react with any 
other insoluble calcium salts that happen to be present.

Give the polarizer a try, I think you will be happy with the results.

Best of luck,

Paul Bradbury
Kamloops, BC,
Canada

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