I thought I got the "wheat flour" from CW Ammen's book. I was surprised but thought I'd try it. I may have misunderstood. I've seen recommendations against talcum powder but with no explanation. I'll go back to talcum powder - I keep it around to lubricate tubes in tires anyway. So far I've been unsuccessful finding reasonably priced foundry supplies. For instance, I can buy a ton of green sand pretty reasonably, but one bag is hard to come by.
Interesting comment you made on furnace atmosphere. Ammen recommended a slightly oxidizing atmosphere and I think my furnace gets enough flow into it to burn neutrally and bleed through all the cracks. Also read about letting the metal heat a few minutes in the crucible. I did that on the second pour but not on the first. I'll try to pour about as soon as I can next time. Thanks for all the comments, guys! I'm not giving up!