Good smelling birch bark tar

[KaniJonas]

Hello,

A few years ago I made my first birch bark tar, the result was fantastic. A nice sweet smell that didn't sting in the nose at all.

Now the 4 times after that it always gets a smoky stinging smell that's not at all as nice.

I did it the same way the first time as the others. The good old "Can dug down and a bucket with birch bark on top."

It's not that strange that the tar gets a smoky smell, rather it's strange that it did not the first time. I mean the birch bark does smoke, even if it gets no air while heated. And that smoke should mix with the oil, which is evaporated before condensing in the can.
The question is, how do I avoid it? And how did I avoid it the first time? I guess there are some factors:

The temperature
The amount of time on the fire
How full the bucket is.
Ventlationholes in the bucket?
How many/how big holes are to the can.
How long the can is.
More?

The first time I did it the bucket tilted a bit, possibly letting smoke out through the bottom. I got very little tar so maybe I only got the first 20 minutes or so, before it got too smoky in there.

I heard the finest tar should look like linseed oil. Has anyone managed this?

 

[KaniJonas]

I just did my seventh try now and I think I'm getting somewhere.

This time I made a hole in the side of the collecting can (can 1, red) and added a 60 cm pipe where smoke could escape.
I made the fire in a slope so I could angle the pipe down. About a minute after starting the fire smoke/steam/gas emerged from the pipe, and shortly after it started dripping oil, which I collected in a glass (can 2, green) underneath. Lots of the gas also went into the glass and some of it condensed and dripped down. I also put a glass (can 3, blue) angled on the other one to collect more of the gas.
After a while the gas stopped and the pipe was just dripping slowly.

This is what I got:
Can 1: 1/2 dl thick, very good smelling tar. A few drops of transparent water.
Can 2: 1/2 dl quite thin (think boiled linseed oil) tar with a little smoky smell.
Can 3: 1/4 dl dark water, not smelling nice at all.


But I'm very excited with the results. It's very interesting that Can 1 got very thick tar, while Can 2 was much thinner. I think the reason Can 2 smelled bad was that it was too close to the pipe so the gas got inside. Next time I will try with a much longer pipe so it has more time to condense. And a longer distance from the pipe to Can 2 so I don't catch the gas. I will also try without Can 1 altogether, directly leading everything into the pipe and out in Can 2. The reason the tar in Can 1 gets thick could be if heat from the fire gets down into the can and turns it into pitch.

 

[Tipi]

i think what you've achieved there is a basic form of fractional distillation, which is what you do to crude oil to make it into bitumen, heavy oils, light oils, diesel and then petrol.

with out going into too much detail (because im not an expert!) its all to do with the length of the molecules and what they do when heated. short ones (like petrol) evaporate more easily than long ones (bitumen or tar). there! knew my degree in geology woud come in handy one day. more reading: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/rocks/fuelsrev3.shtml

ive no idea how this affects the smell though! good luck with future experiments

TP