2 casting sessions ago I started fluxing with sawdust. My lead looked better than I've ever seen it. Then, I cast the following time and the resulting boolits looked dirty.
My technique is to flux with sawdust (about the size of a golf ball) stirring it into the lead fairly aggressively. I scrape the side of the pot and the pour mechanism. I then skim off the sawdust, leaving a mirror finish looking pot of lead. I then sprinkle more sawdust across the top to reduce oxidation. I then start pouring.
Does this sound like the correct technique? Could the "dirt" be ash from the lead (that didn't float to the top)?
Also, I tried covering the pot with foil to reduce oxidation. After pouring a while, I removed the foil and looked in. There was a caramel color on top of the lead. Is covering with foil recommended? And, what was the coloring I saw?