Friday, 12 June 2009

Making Tar from birch bark

I had a go at making tar from birch bark.
So what is this tar good for? Glue, for gluing in arrow tips into the shaft; and it is an antiseptic; but I wanted to extract for waterproofing and preserving wood.
If you have ever burnt the bark you will know it burns very well with lots of black smoke. In bush-craft circles it is known as natures fire lighter. When walking in birch woods you will see fallen trees, the old ones are nothing more than the bark holding a soft sponge of decayed wood. The bark can last for years but the wood can rot out within a year. The bark contains all sorts of tars, oils and resins which are extremely resistant to decay. It is these that I wanted to extract, and so I made a small kiln from a tin with a small hole punched in the bottom.













This tin was placed on a paving slab and metal sheets on blocks so I could put a collecting tin underneath the hole in the bigger tin.














The kiln-tin was filled with birch bark, some of which was rolled up and put in end-on, most of it just stuffed in. In future I will roll all of it up, and place end up in the kiln, as horizontal layers can stop the tar from running out of the hole. The lid must then be placed on the kiln.



















Pile lots of wood and shavings around and over the kiln and set light to it. Add more wood when necessary. Looking at the photo above you can see lots of smoke coming out of the hole. I think I am wasting lots of tar as this smoke stains black, anything it comes into contact with, and is sticky.



















As you can see I have a problem. The smoke and gases coming out of the hole have ignited, and this has also ignited all the collected tar in the tin. This happened a few times, so the next time I will bury the collecting tin in earth to stop air getting to the gasses and smoke, so hopefully no ignition.
The kiln was not very air tight, and as the fire burned down the kiln drew air in through the hole in the bottom. You can see in the photo, a few flames around the tin lid. The bark inside the tin was now obviously alight. I did get some big blobs of tar falling out.















All in all I think that I failed as all I got was a cube centimetre blob of tar. I think I should have got far more.



Stockholm Tar

I would like to try and make Stockholm tar one day. This is extracted from pine tree roots, and Sweden was Europe's most important exporters of this tar. Stockholm tar kept the British Navy afloat by waterproofing the wood on the ships as well as rope and steel. It is still used for treating cuts on animals, and also for soaps for skin ailments.

If anyone knows any more about 'the destructive distillation' of wood, please let me know. Do any charcoal producers set up their kilns so they can also extract the tars? I have only heard of this happening in industrial factory production.