I don't really understand what you're saying but, after smoking three or four joints, I take all the roaches and combine them into another joint with a sprinklin'a'weed on top. Roll it up and smoke it. 3 minutes later = ST0N3D! ^_^

It's like using a bowl and getting resin, when you light the weed and smoke the joint, the resin collects at the back of the joint (where you put your mouth) which is why it gets black/brown. It should also smell like resin by the time you have a roach.
Which is also why it'll get you STOOONED, at least...it does me.