I recently purchased two new large cast iron skillets. After viewing a number of youtube "how to season cast Iron pots", I proceeded to wash one skillet in hot soapy water (as all described). When I dried the pot, I noticed a black residue on the towel, so I washed the pot again and re-dried it and, again, found the black residue on the towel. I have not yet seasoned the pot because of this and in order to use the pot it must first be seasoned.
My questions are: (1) what is this black residue; (2) how may I finally get rid of it; (3) is it dangerous. I