If anyone is interested, there's a least a couple threads on APUG (and maybe one on photo.net) where the difference between photographic grade sodium carbonate and soda ash sodium carbonate are thrashed about...
Edit - I see the thread linked above contains links to the threads I mentioned in it.
For up from the ashes, up from the ashes, grow the roses of success!
You can convert baking soda (sodium bicarbonate) into very pure sodium carbonate by heating it in the oven. Baking soda is USP grade and so contains fewer impurities than washing soda. Place the baking soda in a glass or SS pan and heat it at 350 F for about an hour. Stir it a couple of times during the process. The fine crystals of baking soda will change to a fine fluffy powder of anhyrous sodium carbonate.
so if this is more pure than the "washing soda" I've been using & bicarbonate is much more available....and heating for an hour in the oven is so easy...seems like a good alternative
will the anhydrous absorb water from the air and turn into the monohydrate?