There are much better ways to wash and much better things to use than ammonia.

You loose too much product with an ammonia wash.  There is a ton of info on here about washing spice (and the correct way to wash!) as well as recrystalization. 

For STB crystals I do suggest at least recrystalizing.  Many find them to be extremely harsh to smoke.

If you really do want to wash, do it while your spice is still in the naphtha. Never wash the actual crystals, it accomplishes very little except dissolving perfectly good spice.