The thing I don't feel it was understood is this isn't a stain. It's pure carbon. When you burn a glob of apple juice and sugar in a 375° oven for a time it becomes carbon.
I tried boiling water and salt with dish washing detergent, that made a nice clean black 1/8" thick black blob. I tried a heavy brush and that removed any surface material that was loose. Then I tried 100 grit sandpaper with a lot of energy and force, that got rid of a lot of it and the coating on the cookie sheet.
I'm going to leave it set for a bit with soap, water and salt on it. Then I'm taking it to the shop and hitting it with a ¼" sheet sander. I will do then entire sheet and make it all nice and shiny ( I hope).
If I still had some carbon tetrachloride I know it would have removed it. I don't see spark plug cleaner anymore and the stuff, if it existed today probably wouldn't clean my fingernails.
I appreciate responses to questions and I know they are well intentioned, America is full of helpful people and many are here.
Not everything I try works either, but I keep on trying. Thank you.