The bark of Grey, Paper and to some extent yellow birch are well known for their flamibility and rot resistance. These birches have a high amount of oil in their bark that we can use the same way the birch tree does.
In researching this I found that betulin, the substance often distilled from birches for medicinal uses, which is the wintergreen compound also found in the plant known by that name, may not be the same thing as birch tar. They are, though, both known as birch oil. The more rot resistant birches that we will be using here are know for having a lack of this wintergreen oil in their bark, which is readily detected by smell. Wikipedia tells me birch tar, “… is compounded of phenols such as guaiacol, cresol, xylenol and creosol.” My friend and colleague Jamie from White Memorial Conservation Center and I set out to make the latter, birch tar.
Birch tar has many uses. It was once used in Russia to treat leather, making it water resistant and rot resistant, it can be used similarly to finish wood. Neanderthals and early humans used it as glue for projectiles (when the oil is reduced further it becomes a thermo-plastic, epoxy like substance).
To distill tar from the bark the bark must be heated without it burning, allowing the liquid oil to seperate from the solids in the bark. The oil, which changes viscosity with heat, runs out.
Here’s how we did it;
I collected birch bark from dead grey birch trees, I have an abundance of them in my neighborhood.
I filled this tin Deneen got from goodwill with the bark. There is a multitool on the edge for scale. I had previously poked a hole in the center of the bottom of the tin to allow the tar to run out. It also has a tight fitting lid to keep oxygen out so the bark doesn’t just burn. Buried in the fire pit is another tin can to catch the oil as it drips out.
After placing the tin full of bark directly over the can, we surrounded the container with firewood and lit it. I didn’t get a picture of the fire as it burned which would have been cool.
After about 2 hours we removed the remaining firewood and put out the fire. I enjoyed the anticipation of what we might find.
After carefully removing all components we found a significant amount of oil in the can! Well over a cup. It was similar in consistency and color to motor oil, had a strong, unique smell and felt tacky.
The bark was reduced to this almost glass like material that reminded me of “scale” found on steel after heating. It would not burn. When crushed it was brittle and easily reduced to powder.
We later put the oil in a jar. It continued to thicken as it cooled. I tried it on wood and some leather, it remained somewhat tacky even after some time, darkening the material significantly and adding its characteristic odor. In the future I will reduce it further to make glue for hafting stone points.
It is very cool stuff, and not difficult to make. I have spoken to another colleague who experimented with producing birch tar with only the materials available to neanderthals and early man. I intend to try this myself.