Carding, and boiling at the end

[Bill Graham]

Originally Posted by wayne goerres

The baking soda is used after submersing in the acid bath. Carding is done after boiling and before the acid bath.

I believe it is both. In Flanigan's tutorial, the converted black oxide soot is carded dry, and then there is wet and gentle carding with the baking soda slurry to help remove what the etchant attacks. Regardless of the tutorial, I'm going with the consensus of using steel wool for any stage of carding.