Cast Iron Bread Tin is Leaving Black Spots on Bread? Im using cast iron baking tins for my bread recipe (just standard whole wheat flour, yeast, salt).

I notice that after baking the bread it will have black spots on the bottom and sides.  If I bake the bread further they only get worse.

What is this?  It looks like mold, but I highly doubt that is what it is.  I clean the tins after each use and keep them seasoned and oiled.  Anyone else have this problem?
I think this is just iron reacting with the bread. In cast iron, I think your choices are to either:


line the pan with baking paper (then it's hardly bread anymore ):
heat up the pan to oven temperature first, and then drop in the dough, returning the pan to the oven. This technique is often used with cornbread.