I tried sawdust today as a flux when I smelted some WW. Worked good but it tended to go to the bottom of the pot. It did what I wanted it to do and get the metals back in the mix but it was a little dirty when I got to the bottom of the pot. Bottom line, it works and is cheap. I cast 55 ingots of pure and 46 of WW for about a total of 100 lbs today. Not bad for a morning.