Birchbark can work great for short-term torches. But it has two problems to worry about. One is the heat "cooking" out some of the oils too fast and the excess dripping. The other is the insulating effect of ash on the outside. As the outside layer burns away, the ash builds up and blocks air from getting to the layers below. (Kind of like trying to burn a rolled up newspaper.)
The classic "cresset" was an iron cage type basket into which you tossed pine knots to burn for light. Those pine knots are full of pitch. And if they have enough air-flow, they burn fairly well.
The other versions of torches involve oils and fats soaked into some version of natural fiber, and then burning. That natural fiber just "holds" those oils and fats like a wick. They are what actually burns - as they turn to vapor in the heat.
I've made simple torches by wrapping a couple inches of cotton cloth around the end of a green stick, put a couple twists of wire around to hold it all together, then poured kerosene over it until it is soaked through. It will burn as long as there is still kerosene left in it to burn. I got great light for around 15 minutes, then so-so OK light for another 15 minutes, and then some glowing from the charred smoldering cloth for another 15 minutes.
Those round road-construction barracade torches are actually just an oil lamp. The ball is full of kerosene or diesel fuel. The burner on top has a cloth wick sticking down into the fuel in the ball. The little "cage" on top of the wick/burner just helps keep the wind from blowing out so easily.
Any type of torch requires a fuel, along with something to hold that fuel and function as a wick. When the "fuel" is gone, the "wick" material then burns away.
Those "torches" you see in movies are hollyweird prop creations/versions, and they get changed often in between filming cuts and scenes - to keep up the impression/show. Many have gone to using a propane or LP gas version with the outside disguised to look old.
A torch made from traditional materials just doesn't give off that much light, nor last very long. But they are fun to play with.
Just my humble thoughts to share. Take them as such.
Mikey - yee ol' grumpy blacksmith out in the Hinterlands
p.s. The best true movie interpretation I can recall of a modern use of a torch was in the original Rambo movie when he was trapped inside the mine shaft. He wrapped strips of an old oiled/tarred/greased tarp around a stick to use as a torch, and kept adding more strips as it burned down.
