Well that has shown me a few things
it seams to me that carbon would still be best, you would want to get one of the high carbon pencils if that’s the way you chose to get carbon
12B I think is just about pure carbon (it draws on glass)
then if your I2 still sticks to the carbon then soak in a bit of alcohol, in fact a wash with some alcohol would help to remove allot of salts that may have formed (not NaI though)