I found a nice article about soda firing. https://kazegama.com/soda/ but I am still looking for a good one that talks about borax (which also has sodium in it).
Here are some suggested mixtures for spraying attributed to Gail Nichols :
Here are a couple of mixtures for soda firings:
36 Sodium Carbonate
8 Potassium Carb.
4 Lithium carb
35.30 Soda Ash
7.10 Pearl Ash
4.50 Lithium carb.
The Nichols link didn't work where I took this thread from. Still looking for more articles.