rolling tobacco and joints get a brown liquid substance when burning, but joints have more. Anyone knows what substance does turning the paper brownish?
That's resin dude. As you smoke more and more of the joint it accumulates. It's nothing to worry about.
The resin contributes towards it, it's both tobacco and weed, you get it wether your smoking streight tabs or streight weed in papers.
Look at the filter of a cig after u smoke the whole thing then the crutch of a joint. Its about the same maybe a bit more for the baccy ...and you will shed tears of scarlet.